diff --git a/crypto_kem/babybear/META.yml b/crypto_kem/babybear/META.yml
new file mode 100644
index 00000000..3731bf02
--- /dev/null
+++ b/crypto_kem/babybear/META.yml
@@ -0,0 +1,15 @@
+name: BabyBear
+type: kem
+claimed-nist-level: 1
+claimed-security: IND-CCA2
+length-public-key: 804 
+length-ciphertext: 917
+length-secret-key: 40
+length-shared-secret: 32
+nistkat-sha256: b8442ffaad8e74c6ebfd75d02e13f8db017a7a6dd8458f5d1a5011de6057d775 
+principal-submitters:
+  - Mike Hamburg
+implementations:
+    - name: clean
+      version: round2 
+
diff --git a/crypto_kem/babybear/clean/LICENSE b/crypto_kem/babybear/clean/LICENSE
new file mode 100644
index 00000000..5fb15a7c
--- /dev/null
+++ b/crypto_kem/babybear/clean/LICENSE
@@ -0,0 +1,24 @@
+Copyright (c) 2016-2019 Rambus, Inc.
+and licensed under the following MIT license.
+
+The MIT License (MIT)
+
+Copyright (c) 2016-2019 Rambus Inc.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
diff --git a/crypto_kem/babybear/clean/Makefile b/crypto_kem/babybear/clean/Makefile
new file mode 100644
index 00000000..dbe69c35
--- /dev/null
+++ b/crypto_kem/babybear/clean/Makefile
@@ -0,0 +1,21 @@
+# This Makefile can be used with GNU Make or BSD Make
+
+LIB=libbabybear_clean.a
+
+HEADERS = api.h melas_fec.h params.h ring.h threebears.h
+OBJECTS = kem.o melas_fec.o ring.o threebears.o 
+
+
+CFLAGS=-O3 -Wcast-align=strict -Wall -Wconversion -Wextra -Wpedantic -Wvla -Wmissing-prototypes -Wredundant-decls -std=c99 -I../../../common $(EXTRAFLAGS)
+
+all: $(LIB)
+
+%.o: %.c $(HEADERS)
+	$(CC) $(CFLAGS) -c -o $@ $<
+
+$(LIB): $(OBJECTS)
+	$(AR) -r $@ $(OBJECTS)
+
+clean:
+	$(RM) $(OBJECTS)
+	$(RM) $(LIB)
diff --git a/crypto_kem/babybear/clean/Makefile.Microsoft_nmake b/crypto_kem/babybear/clean/Makefile.Microsoft_nmake
new file mode 100644
index 00000000..27e5cdda
--- /dev/null
+++ b/crypto_kem/babybear/clean/Makefile.Microsoft_nmake
@@ -0,0 +1,19 @@
+# This Makefile can be used with Microsoft Visual Studio's nmake using the command:
+#    nmake /f Makefile.Microsoft_nmake
+
+LIBRARY=libbabybear_clean.lib
+OBJECTS = kem.obj melas_fec.obj ring.obj threebears.obj
+
+CFLAGS=/nologo /I ..\..\..\common /W4 /WX
+
+all: $(LIBRARY)
+
+# Make sure objects are recompiled if headers change.
+$(OBJECTS): *.h
+
+$(LIBRARY): $(OBJECTS)
+	LIB.EXE /NOLOGO /WX /OUT:$@ $**
+
+clean:
+    -DEL $(OBJECTS)
+    -DEL $(LIBRARY)
diff --git a/crypto_kem/babybear/clean/api.h b/crypto_kem/babybear/clean/api.h
new file mode 100644
index 00000000..d513843f
--- /dev/null
+++ b/crypto_kem/babybear/clean/api.h
@@ -0,0 +1,18 @@
+#ifndef PQCLEAN_BABYBEAR_CLEAN_API_H
+#define PQCLEAN_BABYBEAR_CLEAN_API_H
+
+#include <stddef.h>
+#include <stdint.h>
+#include <string.h>
+
+#define PQCLEAN_BABYBEAR_CLEAN_CRYPTO_SECRETKEYBYTES 40
+#define PQCLEAN_BABYBEAR_CLEAN_CRYPTO_PUBLICKEYBYTES 804
+#define PQCLEAN_BABYBEAR_CLEAN_CRYPTO_BYTES 32
+#define PQCLEAN_BABYBEAR_CLEAN_CRYPTO_CIPHERTEXTBYTES 917
+#define PQCLEAN_BABYBEAR_CLEAN_CRYPTO_ALGNAME "BabyBear"
+
+int PQCLEAN_BABYBEAR_CLEAN_crypto_kem_keypair(uint8_t *pk, uint8_t *sk);
+int PQCLEAN_BABYBEAR_CLEAN_crypto_kem_enc(uint8_t *ct, uint8_t *ss, const uint8_t *pk);
+int PQCLEAN_BABYBEAR_CLEAN_crypto_kem_dec(uint8_t *ss, const uint8_t *ct, const uint8_t *sk);
+
+#endif
diff --git a/crypto_kem/babybear/clean/kem.c b/crypto_kem/babybear/clean/kem.c
new file mode 100644
index 00000000..5b9e7ad1
--- /dev/null
+++ b/crypto_kem/babybear/clean/kem.c
@@ -0,0 +1,22 @@
+#include "api.h"
+#include "params.h"
+#include "randombytes.h"
+#include "threebears.h"
+
+int PQCLEAN_BABYBEAR_CLEAN_crypto_kem_keypair(uint8_t *pk, uint8_t *sk) {
+    randombytes(sk, PRIVATE_KEY_BYTES);
+    PQCLEAN_BABYBEAR_CLEAN_get_pubkey(pk, sk);
+    return 0;
+}
+
+int PQCLEAN_BABYBEAR_CLEAN_crypto_kem_enc(uint8_t *ct, uint8_t *ss, const uint8_t *pk) {
+    uint8_t seed[ENC_SEED_BYTES + IV_BYTES];
+    randombytes(seed, sizeof(seed));
+    encapsulate(ss, ct, pk, seed);
+    return 0;
+}
+
+int PQCLEAN_BABYBEAR_CLEAN_crypto_kem_dec(uint8_t *ss, const uint8_t *ct, const uint8_t *sk) {
+    PQCLEAN_BABYBEAR_CLEAN_decapsulate(ss, ct, sk);
+    return 0;
+}
diff --git a/crypto_kem/babybear/clean/melas_fec.c b/crypto_kem/babybear/clean/melas_fec.c
new file mode 100644
index 00000000..ace39b9c
--- /dev/null
+++ b/crypto_kem/babybear/clean/melas_fec.c
@@ -0,0 +1,87 @@
+/* Melas forward error correction, reference code (as implemented in the paper) */
+#include "melas_fec.h"
+
+/* Return s/2^n mod R */
+static fec_gf_t step(size_t n, fec_gf_t R, fec_gf_t s) {
+    for (; n; n--) {
+        s = (s ^ ((s & 1) * R)) >> 1;
+    }
+    return s;
+}
+
+/* Compute syndrome(data), where data has length len */
+#define syndrome18(data,len) s18update(0,data,len)
+static fec_gf_t s18update(fec_gf_t r, const uint8_t *data, size_t len) {
+    for (size_t i = 0; i < len; i++) {
+        r = step(8, 0x46231, r ^ data[i]);
+    }
+    return r;
+}
+
+/* Append 3 bytes of FEC(data) to data, so that the FEC becomes 0 */
+void PQCLEAN_BABYBEAR_CLEAN_melas_fec_set(
+    uint8_t out[MELAS_FEC_BYTES],
+    const uint8_t *data,
+    size_t len
+) {
+    fec_gf_t fec = syndrome18(data, len);
+    for (size_t i = 0; i < MELAS_FEC_BYTES; i++, fec >>= 8) {
+        out[i] = (uint8_t)fec;
+    }
+}
+
+/* Return a*b mod Q */
+static fec_gf_t mul(fec_gf_t a, fec_gf_t b) {
+    fec_gf_t r = 0;
+    for (size_t i = 0; i < 9; i++) {
+        r ^= ((b >> (8 - i)) & 1) * a;
+        a = step(1, Q, a);
+    }
+    return r;
+}
+
+/* Reverse an 18-bit number x */
+static fec_gf_t reverse18(fec_gf_t x) {
+    fec_gf_t ret = 0;
+    for (size_t i = 0; i < 18; i++) {
+        ret ^= ((x >> i) & 1) << (17 - i);
+    }
+    return ret;
+}
+
+/* Correct data to have the given FEC */
+void PQCLEAN_BABYBEAR_CLEAN_melas_fec_correct (
+    uint8_t *data,
+    size_t len,
+    const uint8_t fec[MELAS_FEC_BYTES]
+) {
+
+    fec_gf_t a = s18update(syndrome18(data, len), fec, MELAS_FEC_BYTES);
+    fec_gf_t c, r, htr;
+    size_t i;
+    const uint8_t table[9] = {36, 10, 43, 215, 52, 11, 116, 244, 0};
+    fec_gf_t e0, e1;
+
+    /* Form a quadratic equation from the syndrome */
+    c = mul(step(9, Q, a), step(9, Q, reverse18(a)));
+    for (i = 0, r = 0x100; i < 510; i++) {
+        r = mul(r, c);
+    }
+    r = step(17, Q, r);
+    a = step(511 - (len + MELAS_FEC_BYTES) * 8, Q, a);
+
+    /* Solve using the half trace */
+    for (i = 0, htr = 0; i < 9; i++) {
+        htr ^= ((r >> i) & 1) * table[i];
+    }
+    e0 = mul(a, htr);
+    e1 = e0 ^ a;
+
+    /* Correct the errors using the locators */
+    for (i = 0; i < len; i++) {
+        data[i] ^= (uint8_t)(e0 & (((e0 & (e0 - 1)) - 1) >> 9));
+        data[i] ^= (uint8_t)(e1 & (((e1 & (e1 - 1)) - 1) >> 9));
+        e0 = step(8, Q, e0);
+        e1 = step(8, Q, e1);
+    }
+}
diff --git a/crypto_kem/babybear/clean/melas_fec.h b/crypto_kem/babybear/clean/melas_fec.h
new file mode 100644
index 00000000..c44638bc
--- /dev/null
+++ b/crypto_kem/babybear/clean/melas_fec.h
@@ -0,0 +1,26 @@
+#ifndef __THREEBEARS_MELAS_FEC_H__
+#define __THREEBEARS_MELAS_FEC_H__
+
+#include "api.h"
+
+#define MELAS_FEC_BYTES 3
+#define MELAS_FEC_BITS 18
+
+typedef uint32_t fec_gf_t;
+static const fec_gf_t Q = 0x211;
+
+/* Append 3 bytes of FEC(data) to data, so that the FEC becomes 0 */
+void PQCLEAN_BABYBEAR_CLEAN_melas_fec_set(
+    uint8_t out[MELAS_FEC_BYTES],
+    const uint8_t *data,
+    size_t len
+);
+
+/* Append 3 bytes of FEC(data) to data, so that the FEC becomes 0 */
+void PQCLEAN_BABYBEAR_CLEAN_melas_fec_correct(
+    uint8_t *data,
+    size_t len,
+    const uint8_t fec[MELAS_FEC_BYTES]
+);
+
+#endif
diff --git a/crypto_kem/babybear/clean/params.h b/crypto_kem/babybear/clean/params.h
new file mode 100644
index 00000000..b99c2fa3
--- /dev/null
+++ b/crypto_kem/babybear/clean/params.h
@@ -0,0 +1,29 @@
+#ifndef __THREEBEARS_PARAMS_H__
+#define __THREEBEARS_PARAMS_H__
+
+#define VERSION              1
+#define MATRIX_SEED_BYTES    24
+#define ENC_SEED_BYTES       32
+#define IV_BYTES             0
+#define LGX                  10
+#define DIGITS               312
+#define DIM                  2
+#define VAR_TIMES_128        72
+#define LPR_BITS             4
+#define FEC_BITS             18
+#define CCA                  1
+#define SHARED_SECRET_BYTES  32
+#define PRIVATE_KEY_BYTES    40
+#define PRF_KEY_BYTES        PRIVATE_KEY_BYTES
+
+#define BEAR_NAME   "BabyBear"
+#define encapsulate PQCLEAN_BABYBEAR_CLEAN_encapsulate
+#define decapsulate PQCLEAN_BABYBEAR_CLEAN_decapsulate
+#define get_pubkey  PQCLEAN_BABYBEAR_CLEAN_get_pubkey
+
+#define GF_BYTES ((LGX*DIGITS+7)/8)
+#define PUBLIC_KEY_BYTES (MATRIX_SEED_BYTES + DIM*GF_BYTES)
+#define CAPSULE_BYTES \
+    (DIM*GF_BYTES + IV_BYTES + ((ENC_SEED_BYTES*8+FEC_BITS)*LPR_BITS+7)/8)
+
+#endif
diff --git a/crypto_kem/babybear/clean/ring.c b/crypto_kem/babybear/clean/ring.c
new file mode 100644
index 00000000..03c4ad64
--- /dev/null
+++ b/crypto_kem/babybear/clean/ring.c
@@ -0,0 +1,102 @@
+/** Ring arithmetic implementation */
+#include "ring.h"
+
+/** Multiply and accumulate c += a*b */
+void PQCLEAN_BABYBEAR_CLEAN_mac(gf_t c, const gf_t a, const gf_t b) {
+    /* Reference non-Karatsuba MAC */
+    dslimb_t accum[2 * DIGITS] = {0};
+    dslimb_t chain;
+    size_t i, j;
+
+    /* Initialize accumulator = unclarify(c) */
+    for (i = 0; i < DIGITS; i++) {
+        accum[i + DIGITS / 2] = c[i];
+    }
+
+    /* Multiply */
+    for (i = 0; i < DIGITS; i++) {
+        for (j = 0; j < DIGITS; j++) {
+            accum[i + j] += (dslimb_t)a[i] * b[j];
+        }
+    }
+
+    /* Clarify and reduce */
+    for (i = 0; i < DIGITS / 2; i++) {
+        accum[i + DIGITS / 2] -= accum[i];
+        accum[i + DIGITS]   += accum[i];
+        accum[i + DIGITS / 2] += accum[i + 3 * DIGITS / 2];
+        accum[i + DIGITS]   += accum[i + 3 * DIGITS / 2];
+    }
+
+    /* Carry propagate */
+    chain = accum[3 * DIGITS / 2 - 1];
+    accum[3 * DIGITS / 2 - 1] = chain & LMASK;
+    chain >>= LGX;
+    accum[DIGITS] += chain;
+    for (i = DIGITS / 2; i < 3 * DIGITS / 2; i++) {
+        chain += accum[i];
+        c[i - DIGITS / 2] = chain & LMASK;
+        chain >>= LGX;
+    }
+    c[0] = (limb_t) (c[0] + chain);
+    c[DIGITS / 2] = (limb_t) (c[DIGITS / 2] + chain);
+}
+
+/** Reduce a gf_t to canonical form, i.e. strictly less than N. */
+void PQCLEAN_BABYBEAR_CLEAN_canon(gf_t c) {
+    const limb_t DELTA = (limb_t)1 << (LGX - 1);
+    slimb_t hi;
+    dslimb_t scarry;
+    dlimb_t carry;
+
+    /* Reduce to 0..2p */
+    hi = (slimb_t) (c[DIGITS - 1] - DELTA);
+    c[DIGITS - 1] = (limb_t) ((hi & LMASK) + DELTA);
+    c[DIGITS / 2] = (limb_t) (c[DIGITS / 2] + (hi >> LGX));
+
+    /* Strong reduce.  First subtract modulus */
+    scarry = hi >> LGX;
+    for (size_t i = 0; i < DIGITS; i++) {
+        scarry = scarry + (slimb_t)c[i] - modulus(i);
+        c[i] = scarry & LMASK;
+        scarry >>= LGX;
+    }
+
+    /* add it back */
+    carry = 0;
+    for (size_t i = 0; i < DIGITS; i++) {
+        carry = carry + c[i] + ((dlimb_t)scarry & modulus(i));
+        c[i] = carry & LMASK;
+        carry >>= LGX;
+    }
+}
+
+/** Serialize a gf_t to bytes */
+void PQCLEAN_BABYBEAR_CLEAN_contract(uint8_t ch[GF_BYTES], gf_t a) {
+    size_t pos;
+
+    PQCLEAN_BABYBEAR_CLEAN_canon(a);
+    for (size_t i = 0; i < GF_BYTES; i++) {
+        pos = (i * 8) / LGX;
+        ch[i] = (uint8_t)(a[pos] >> ((i * 8) % LGX));
+        if (i < GF_BYTES - 1) {
+            ch[i] |= (uint8_t)(a[pos + 1] << (LGX - ((i * 8) % LGX)));
+        }
+    }
+}
+
+/** Deserialize a gf_t from bytes */
+void PQCLEAN_BABYBEAR_CLEAN_expand(gf_t ll, const uint8_t ch[GF_BYTES]) {
+    limb_t tmp, buffer = 0;
+
+    for (size_t i = 0, j = 0, bbits = 0; i < GF_BYTES; i++) {
+        tmp = ch[i];
+        buffer |= (limb_t)(tmp << bbits);
+        bbits += 8;
+        if (bbits >= LGX) {
+            ll[j++] = buffer & LMASK;
+            buffer = (limb_t)(tmp >> (LGX - (bbits - 8)));
+            bbits = bbits - LGX;
+        }
+    }
+}
diff --git a/crypto_kem/babybear/clean/ring.h b/crypto_kem/babybear/clean/ring.h
new file mode 100644
index 00000000..8cbc207c
--- /dev/null
+++ b/crypto_kem/babybear/clean/ring.h
@@ -0,0 +1,31 @@
+#ifndef __THREEBEARS_RING_H__
+#define __THREEBEARS_RING_H__
+
+#include "api.h"
+#include "params.h"
+
+typedef uint16_t limb_t;
+typedef int16_t slimb_t;
+typedef uint32_t dlimb_t;
+typedef int32_t dslimb_t;
+#define LMASK (((limb_t)1<<LGX)-1)
+typedef limb_t gf_t[DIGITS];
+
+/* Serialize a gf_t */
+void PQCLEAN_BABYBEAR_CLEAN_contract(uint8_t ch[GF_BYTES], gf_t a);
+
+/* Deserialize a gf_t */
+void PQCLEAN_BABYBEAR_CLEAN_expand(gf_t ll, const uint8_t ch[GF_BYTES]);
+
+/* Multiply and accumulate c = c + a*b */
+void PQCLEAN_BABYBEAR_CLEAN_mac(gf_t c, const gf_t a, const gf_t b);
+
+/* Reduce ring element to canonical form */
+void PQCLEAN_BABYBEAR_CLEAN_canon(gf_t c);
+
+/** Return the i'th limb of the modulus */
+static inline limb_t modulus(size_t i) {
+    return (i == DIGITS / 2) ? LMASK - 1 : LMASK;
+}
+
+#endif
diff --git a/crypto_kem/babybear/clean/threebears.c b/crypto_kem/babybear/clean/threebears.c
new file mode 100644
index 00000000..b35d4ff1
--- /dev/null
+++ b/crypto_kem/babybear/clean/threebears.c
@@ -0,0 +1,225 @@
+/** ThreeBears reference implementation */
+#include "api.h"
+#include "melas_fec.h"
+#include "params.h"
+#include "ring.h"
+#include "sp800-185.h"
+#include "threebears.h"
+
+#define FEC_BYTES ((FEC_BITS+7)/8)
+#define ENC_BITS  (ENC_SEED_BYTES*8 + FEC_BITS)
+
+enum { HASH_PURPOSE_UNIFORM = 0, HASH_PURPOSE_KEYGEN = 1, HASH_PURPOSE_ENCAPS = 2, HASH_PURPOSE_PRF = 3 };
+
+/** Initialize the hash function with a given purpose */
+static void threebears_hash_init(
+    shake256incctx *ctx,
+    uint8_t purpose
+) {
+    const unsigned char S[] = "ThreeBears";
+    const uint8_t pblock[15] = {
+        VERSION, PRIVATE_KEY_BYTES, MATRIX_SEED_BYTES, ENC_SEED_BYTES,
+        IV_BYTES, SHARED_SECRET_BYTES, LGX, DIGITS & 0xFF, DIGITS >> 8, DIM,
+                VAR_TIMES_128 - 1, LPR_BITS, FEC_BITS, CCA, 0 /* padding */
+    };
+
+    cshake256_inc_init(ctx, NULL, 0, (const uint8_t *)S, sizeof(S) - 1);
+    cshake256_inc_absorb(ctx, (const uint8_t *)pblock, sizeof(pblock));
+    cshake256_inc_absorb(ctx, &purpose, 1);
+}
+
+/** Sample n gf_t's uniformly from a seed */
+static void uniform(gf_t matrix, const uint8_t *seed, uint8_t iv) {
+    uint8_t c[GF_BYTES];
+    shake256incctx ctx;
+
+    threebears_hash_init(&ctx, HASH_PURPOSE_UNIFORM);
+    cshake256_inc_absorb(&ctx, seed, MATRIX_SEED_BYTES);
+    cshake256_inc_absorb(&ctx, &iv, 1);
+    cshake256_inc_finalize(&ctx);
+    cshake256_inc_squeeze(c, sizeof(c), &ctx);
+    PQCLEAN_BABYBEAR_CLEAN_expand(matrix, c);
+}
+
+/** The ThreeBears error distribution */
+static slimb_t psi(uint8_t ci) {
+    int sample = 0, var = VAR_TIMES_128;
+
+    for (; var > 64; var -= 64, ci = (uint8_t)(ci << 2)) {
+        sample += ((ci + 64) >> 8) + ((ci - 64) >> 8);
+    }
+    return (slimb_t)(sample + ((ci + var) >> 8) + ((ci - var) >> 8));
+}
+
+/** Sample a vector of n noise elements */
+static void noise(gf_t x, const shake256incctx *ctx, uint8_t iv) {
+    uint8_t c[DIGITS];
+    shake256incctx ctx2;
+
+    memcpy(&ctx2, ctx, sizeof(ctx2));
+    cshake256_inc_absorb(&ctx2, &iv, 1);
+    cshake256_inc_finalize(&ctx2);
+    cshake256_inc_squeeze(c, DIGITS, &ctx2);
+    for (size_t i = 0; i < DIGITS; i++) {
+        x[i] = (limb_t)(psi(c[i]) + modulus(i));
+    }
+}
+
+/* Expand public key from private key */
+void PQCLEAN_BABYBEAR_CLEAN_get_pubkey(uint8_t *pk, const uint8_t *sk) {
+    shake256incctx ctx;
+    shake256incctx ctx2;
+    gf_t sk_expanded[DIM], b, c;
+
+    threebears_hash_init(&ctx, HASH_PURPOSE_KEYGEN);
+    cshake256_inc_absorb(&ctx, sk, PRIVATE_KEY_BYTES);
+
+    memcpy(&ctx2, &ctx, sizeof(ctx2));
+    cshake256_inc_finalize(&ctx2);
+    cshake256_inc_squeeze(pk, MATRIX_SEED_BYTES, &ctx2);
+
+    for (uint8_t i = 0; i < DIM; i++) {
+        noise(sk_expanded[i], &ctx, i);
+    }
+    for (uint8_t i = 0; i < DIM; i++) {
+        noise(c, &ctx, (uint8_t)(i + DIM));
+        for (uint8_t j = 0; j < DIM; j++) {
+            uniform(b, pk, (uint8_t) (i + DIM * j));
+            PQCLEAN_BABYBEAR_CLEAN_mac(c, b, sk_expanded[j]);
+        }
+        PQCLEAN_BABYBEAR_CLEAN_contract(&pk[MATRIX_SEED_BYTES + i * GF_BYTES], c);
+    }
+}
+
+/* Encapsulate a shared secret and return it */
+void PQCLEAN_BABYBEAR_CLEAN_encapsulate(
+    uint8_t *shared_secret,
+    uint8_t *capsule,
+    const uint8_t *pk,
+    const uint8_t *seed
+) {
+    uint8_t *lpr_data = &capsule[GF_BYTES * DIM];
+    shake256incctx ctx;
+    gf_t sk_expanded[DIM], b, c;
+    uint8_t tbi[ENC_SEED_BYTES + FEC_BYTES];
+    dlimb_t rlimb0, rlimb1;
+    limb_t h;
+    uint8_t *iv = &lpr_data[(ENC_BITS * LPR_BITS + 7) / 8];
+
+    memcpy(iv, &seed[ENC_SEED_BYTES], IV_BYTES);
+
+    threebears_hash_init(&ctx, HASH_PURPOSE_ENCAPS);
+    cshake256_inc_absorb(&ctx, pk, MATRIX_SEED_BYTES);
+    cshake256_inc_absorb(&ctx, seed, ENC_SEED_BYTES + IV_BYTES);
+
+    for (uint8_t i = 0; i < DIM; i++) {
+        noise(sk_expanded[i], &ctx, i);
+    }
+    for (uint8_t i = 0; i < DIM; i++) {
+        noise(c, &ctx, (uint8_t)(i + DIM));
+        for (uint8_t j = 0; j < DIM; j++) {
+            uniform(b, pk, (uint8_t)(j + DIM * i));
+            PQCLEAN_BABYBEAR_CLEAN_mac(c, b, sk_expanded[j]);
+        }
+        PQCLEAN_BABYBEAR_CLEAN_contract(&capsule[i * GF_BYTES], c);
+    }
+    noise(c, &ctx, (uint8_t)(2 * DIM));
+
+    /* Calculate approximate shared secret */
+    for (uint8_t i = 0; i < DIM; i++) {
+        PQCLEAN_BABYBEAR_CLEAN_expand(b, &pk[MATRIX_SEED_BYTES + i * GF_BYTES]);
+        PQCLEAN_BABYBEAR_CLEAN_mac(c, b, sk_expanded[i]);
+    }
+    PQCLEAN_BABYBEAR_CLEAN_canon(c);
+
+
+    memcpy(tbi, seed, ENC_SEED_BYTES);
+
+    PQCLEAN_BABYBEAR_CLEAN_melas_fec_set(&tbi[ENC_SEED_BYTES], tbi, ENC_SEED_BYTES);
+
+    /* Export with rounding */
+    for (size_t i = 0; i < ENC_BITS; i += 2) {
+        h = (limb_t)(tbi[i / 8] >> (i % 8));
+        rlimb0 = (dlimb_t)((c[i / 2]          >> (LGX - LPR_BITS)) + (h << 3));
+        rlimb1 = (dlimb_t)((c[DIGITS - i / 2 - 1] >> (LGX - LPR_BITS)) + ((h >> 1) << 3));
+        lpr_data[i / 2] = (uint8_t)((rlimb0 & 0xF) | rlimb1 << 4);
+    }
+
+    cshake256_inc_finalize(&ctx);
+    cshake256_inc_squeeze(shared_secret, SHARED_SECRET_BYTES, &ctx);
+}
+
+/* Decapsulate a shared secret and return it */
+void PQCLEAN_BABYBEAR_CLEAN_decapsulate(
+    uint8_t shared_secret[SHARED_SECRET_BYTES],
+    const uint8_t capsule[CAPSULE_BYTES],
+    const uint8_t sk[PRIVATE_KEY_BYTES]
+) {
+    const uint8_t *lpr_data = &capsule[GF_BYTES * DIM];
+    shake256incctx ctx;
+    gf_t ska, b, c = {0};
+    uint8_t seed[ENC_SEED_BYTES + FEC_BYTES + IV_BYTES];
+    limb_t rounding, out;
+    size_t j;
+    limb_t our_rlimb, their_rlimb, delta;
+    uint8_t pk[PUBLIC_KEY_BYTES], capsule2[CAPSULE_BYTES];
+    uint8_t ret, ok, sep, prfk[PRF_KEY_BYTES];
+    uint8_t prfout[SHARED_SECRET_BYTES];
+
+    /* Calculate approximate shared secret */
+    threebears_hash_init(&ctx, HASH_PURPOSE_KEYGEN);
+    cshake256_inc_absorb(&ctx, sk, PRIVATE_KEY_BYTES);
+
+    for (uint8_t i = 0; i < DIM; i++) {
+        PQCLEAN_BABYBEAR_CLEAN_expand(b, &capsule[i * GF_BYTES]);
+        noise(ska, &ctx, i);
+        PQCLEAN_BABYBEAR_CLEAN_mac(c, ska, b);
+    }
+
+    /* Recover seed from LPR data */
+    PQCLEAN_BABYBEAR_CLEAN_canon(c);
+    rounding = 1 << (LPR_BITS - 1);
+    out = 0;
+    for (int32_t i = ENC_BITS - 1; i >= 0; i--) {
+        j = (size_t) ((i & 1) ? DIGITS - i / 2 - 1 : i / 2);
+        our_rlimb = (limb_t)(c[j] >> (LGX - LPR_BITS - 1));
+        their_rlimb = (limb_t)(lpr_data[i * LPR_BITS / 8] >> ((i * LPR_BITS) % 8));
+        delta =  (limb_t)(their_rlimb * 2 - our_rlimb + rounding);
+        out |= (limb_t)(((delta >> LPR_BITS) & 1) << (i % 8));
+        if (i % 8 == 0) {
+            seed[i / 8] = (uint8_t)out;
+            out = 0;
+        }
+    }
+    PQCLEAN_BABYBEAR_CLEAN_melas_fec_correct(seed, ENC_SEED_BYTES, &seed[ENC_SEED_BYTES]);
+
+    /* Re-encapsulate and check; encapsulate will compute the shared secret */
+    //pk[PUBLIC_KEY_BYTES], capsule2[CAPSULE_BYTES];
+    PQCLEAN_BABYBEAR_CLEAN_get_pubkey(pk, sk);
+    memcpy(&seed[ENC_SEED_BYTES], &lpr_data[(ENC_BITS * LPR_BITS + 7) / 8], IV_BYTES);
+    PQCLEAN_BABYBEAR_CLEAN_encapsulate(shared_secret, capsule2, pk, seed);
+
+    /* Check capsule == capsule2 in constant time */
+    ret = 0;
+    for (size_t i = 0; i < CAPSULE_BYTES; i++) {
+        ret |= capsule[i] ^ capsule2[i];
+    }
+    ok = (uint8_t)(((int)ret - 1) >> 8);
+
+    /* Calculate PRF key */
+    sep = 0xFF;
+    cshake256_inc_absorb(&ctx, &sep, 1);
+    cshake256_inc_finalize(&ctx);
+    cshake256_inc_squeeze(prfk, PRF_KEY_BYTES, &ctx);
+
+    /* Calculate PRF */
+    threebears_hash_init(&ctx, HASH_PURPOSE_PRF);
+    cshake256_inc_absorb(&ctx, prfk, PRF_KEY_BYTES);
+    cshake256_inc_absorb(&ctx, capsule, CAPSULE_BYTES);
+    cshake256_inc_finalize(&ctx);
+    cshake256_inc_squeeze(prfout, SHARED_SECRET_BYTES, &ctx);
+
+    for (size_t i = 0; i < SHARED_SECRET_BYTES; i++) {
+        shared_secret[i] = (uint8_t)((shared_secret[i] & ok) | (prfout[i] & ~ok));
+    }
+}
diff --git a/crypto_kem/babybear/clean/threebears.h b/crypto_kem/babybear/clean/threebears.h
new file mode 100644
index 00000000..1f345b28
--- /dev/null
+++ b/crypto_kem/babybear/clean/threebears.h
@@ -0,0 +1,60 @@
+#ifndef __THREE_BEARS_BABYBEAR_H__
+#define __THREE_BEARS_BABYBEAR_H__
+
+#include <stddef.h> /* for size_t */
+#include <stdint.h>
+
+#define BABYBEAR_KEYGEN_SEED_BYTES 40
+#define BABYBEAR_PRIVATE_KEY_BYTES BABYBEAR_KEYGEN_SEED_BYTES
+#define BABYBEAR_SHARED_SECRET_BYTES 32
+#define BABYBEAR_ENC_SEED_AND_IV_BYTES 32
+#define BABYBEAR_PUBLIC_KEY_BYTES 804
+#define BABYBEAR_CAPSULE_BYTES 917
+
+/**
+ * Expand a secret seed to a public/private keypair.
+ *
+ * @param[out] pk The public key.
+ * @param[in] sk The private key, which must be uniformly random.
+ */
+void PQCLEAN_BABYBEAR_CLEAN_get_pubkey (
+    uint8_t pk[BABYBEAR_PUBLIC_KEY_BYTES],
+    const uint8_t sk[BABYBEAR_PRIVATE_KEY_BYTES]
+);
+
+/**
+ * Create a shared secret using a random seed and another party's public key.
+ *
+ * Input and output parameters may not alias.
+ *
+ * @param[out] shared_secret The shared secret key.
+ * @param[out] capsule A ciphertext to send to the other party.
+ * @param[in] pk The other party's public key.
+ * @param[in] seed A random seed.
+ */
+void PQCLEAN_BABYBEAR_CLEAN_encapsulate (
+    uint8_t shared_secret[BABYBEAR_SHARED_SECRET_BYTES],
+    uint8_t capsule[BABYBEAR_CAPSULE_BYTES],
+    const uint8_t pk[BABYBEAR_PUBLIC_KEY_BYTES],
+    const uint8_t seed[BABYBEAR_ENC_SEED_AND_IV_BYTES]
+);
+
+/**
+ * Extract the shared secret from a capsule using the private key.
+ * Has a negligible but nonzero probability of failure.
+ *
+ * Input and output parameters may not alias.
+ *
+ * @param[out] shared_secret The shared secret.
+ * @param[in] capsule The capsule produced by encapsulate_cca2.
+ * @param[in] sk The private key.
+ */
+void PQCLEAN_BABYBEAR_CLEAN_decapsulate (
+    uint8_t shared_secret[BABYBEAR_SHARED_SECRET_BYTES],
+    const uint8_t capsule[BABYBEAR_CAPSULE_BYTES],
+    const uint8_t sk[BABYBEAR_PRIVATE_KEY_BYTES]
+);
+
+void PQCLEAN_BABYBEAR_CLEAN_secure_bzero (void *s, size_t size);
+
+#endif
diff --git a/crypto_kem/mamabear/META.yml b/crypto_kem/mamabear/META.yml
new file mode 100644
index 00000000..c9200c4f
--- /dev/null
+++ b/crypto_kem/mamabear/META.yml
@@ -0,0 +1,15 @@
+name: MamaBear
+type: kem
+claimed-nist-level: 3
+claimed-security: IND-CCA2
+length-public-key: 1194 
+length-ciphertext: 1307
+length-secret-key: 40
+length-shared-secret: 32
+nistkat-sha256: 2161de5015dc0477106b71ba17498982f77fae127fce724496c8a587803b1839 
+principal-submitters:
+  - Mike Hamburg
+implementations:
+    - name: clean
+      version: round2 
+
diff --git a/crypto_kem/mamabear/clean/LICENSE b/crypto_kem/mamabear/clean/LICENSE
new file mode 100644
index 00000000..5fb15a7c
--- /dev/null
+++ b/crypto_kem/mamabear/clean/LICENSE
@@ -0,0 +1,24 @@
+Copyright (c) 2016-2019 Rambus, Inc.
+and licensed under the following MIT license.
+
+The MIT License (MIT)
+
+Copyright (c) 2016-2019 Rambus Inc.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
diff --git a/crypto_kem/mamabear/clean/Makefile b/crypto_kem/mamabear/clean/Makefile
new file mode 100644
index 00000000..917c0c2e
--- /dev/null
+++ b/crypto_kem/mamabear/clean/Makefile
@@ -0,0 +1,21 @@
+# This Makefile can be used with GNU Make or BSD Make
+
+LIB=libmamabear_clean.a
+
+HEADERS = api.h melas_fec.h params.h ring.h threebears.h
+OBJECTS = kem.o melas_fec.o ring.o threebears.o 
+
+
+CFLAGS=-O3 -Wcast-align=strict -Wall -Wconversion -Wextra -Wpedantic -Wvla -Wmissing-prototypes -Wredundant-decls -std=c99 -I../../../common $(EXTRAFLAGS)
+
+all: $(LIB)
+
+%.o: %.c $(HEADERS)
+	$(CC) $(CFLAGS) -c -o $@ $<
+
+$(LIB): $(OBJECTS)
+	$(AR) -r $@ $(OBJECTS)
+
+clean:
+	$(RM) $(OBJECTS)
+	$(RM) $(LIB)
diff --git a/crypto_kem/mamabear/clean/Makefile.Microsoft_nmake b/crypto_kem/mamabear/clean/Makefile.Microsoft_nmake
new file mode 100644
index 00000000..164de00d
--- /dev/null
+++ b/crypto_kem/mamabear/clean/Makefile.Microsoft_nmake
@@ -0,0 +1,19 @@
+# This Makefile can be used with Microsoft Visual Studio's nmake using the command:
+#    nmake /f Makefile.Microsoft_nmake
+
+LIBRARY=libmamabear_clean.lib
+OBJECTS = kem.obj melas_fec.obj ring.obj threebears.obj
+
+CFLAGS=/nologo /I ..\..\..\common /W4 /WX
+
+all: $(LIBRARY)
+
+# Make sure objects are recompiled if headers change.
+$(OBJECTS): *.h
+
+$(LIBRARY): $(OBJECTS)
+	LIB.EXE /NOLOGO /WX /OUT:$@ $**
+
+clean:
+    -DEL $(OBJECTS)
+    -DEL $(LIBRARY)
diff --git a/crypto_kem/mamabear/clean/api.h b/crypto_kem/mamabear/clean/api.h
new file mode 100644
index 00000000..135b3607
--- /dev/null
+++ b/crypto_kem/mamabear/clean/api.h
@@ -0,0 +1,18 @@
+#ifndef PQCLEAN_MAMABEAR_CLEAN_API_H
+#define PQCLEAN_MAMABEAR_CLEAN_API_H
+
+#include <stddef.h>
+#include <stdint.h>
+#include <string.h>
+
+#define PQCLEAN_MAMABEAR_CLEAN_CRYPTO_SECRETKEYBYTES 40
+#define PQCLEAN_MAMABEAR_CLEAN_CRYPTO_PUBLICKEYBYTES 1194
+#define PQCLEAN_MAMABEAR_CLEAN_CRYPTO_BYTES 32
+#define PQCLEAN_MAMABEAR_CLEAN_CRYPTO_CIPHERTEXTBYTES 1307
+#define PQCLEAN_MAMABEAR_CLEAN_CRYPTO_ALGNAME "MamaBear"
+
+int PQCLEAN_MAMABEAR_CLEAN_crypto_kem_keypair(uint8_t *pk, uint8_t *sk);
+int PQCLEAN_MAMABEAR_CLEAN_crypto_kem_enc(uint8_t *ct, uint8_t *ss, const uint8_t *pk);
+int PQCLEAN_MAMABEAR_CLEAN_crypto_kem_dec(uint8_t *ss, const uint8_t *ct, const uint8_t *sk);
+
+#endif
diff --git a/crypto_kem/mamabear/clean/kem.c b/crypto_kem/mamabear/clean/kem.c
new file mode 100644
index 00000000..9e40065f
--- /dev/null
+++ b/crypto_kem/mamabear/clean/kem.c
@@ -0,0 +1,22 @@
+#include "api.h"
+#include "params.h"
+#include "randombytes.h"
+#include "threebears.h"
+
+int PQCLEAN_MAMABEAR_CLEAN_crypto_kem_keypair(uint8_t *pk, uint8_t *sk) {
+    randombytes(sk, PRIVATE_KEY_BYTES);
+    PQCLEAN_MAMABEAR_CLEAN_get_pubkey(pk, sk);
+    return 0;
+}
+
+int PQCLEAN_MAMABEAR_CLEAN_crypto_kem_enc(uint8_t *ct, uint8_t *ss, const uint8_t *pk) {
+    uint8_t seed[ENC_SEED_BYTES + IV_BYTES];
+    randombytes(seed, sizeof(seed));
+    encapsulate(ss, ct, pk, seed);
+    return 0;
+}
+
+int PQCLEAN_MAMABEAR_CLEAN_crypto_kem_dec(uint8_t *ss, const uint8_t *ct, const uint8_t *sk) {
+    PQCLEAN_MAMABEAR_CLEAN_decapsulate(ss, ct, sk);
+    return 0;
+}
diff --git a/crypto_kem/mamabear/clean/melas_fec.c b/crypto_kem/mamabear/clean/melas_fec.c
new file mode 100644
index 00000000..80e33604
--- /dev/null
+++ b/crypto_kem/mamabear/clean/melas_fec.c
@@ -0,0 +1,87 @@
+/* Melas forward error correction, reference code (as implemented in the paper) */
+#include "melas_fec.h"
+
+/* Return s/2^n mod R */
+static fec_gf_t step(size_t n, fec_gf_t R, fec_gf_t s) {
+    for (; n; n--) {
+        s = (s ^ ((s & 1) * R)) >> 1;
+    }
+    return s;
+}
+
+/* Compute syndrome(data), where data has length len */
+#define syndrome18(data,len) s18update(0,data,len)
+static fec_gf_t s18update(fec_gf_t r, const uint8_t *data, size_t len) {
+    for (size_t i = 0; i < len; i++) {
+        r = step(8, 0x46231, r ^ data[i]);
+    }
+    return r;
+}
+
+/* Append 3 bytes of FEC(data) to data, so that the FEC becomes 0 */
+void PQCLEAN_MAMABEAR_CLEAN_melas_fec_set(
+    uint8_t out[MELAS_FEC_BYTES],
+    const uint8_t *data,
+    size_t len
+) {
+    fec_gf_t fec = syndrome18(data, len);
+    for (size_t i = 0; i < MELAS_FEC_BYTES; i++, fec >>= 8) {
+        out[i] = (uint8_t)fec;
+    }
+}
+
+/* Return a*b mod Q */
+static fec_gf_t mul(fec_gf_t a, fec_gf_t b) {
+    fec_gf_t r = 0;
+    for (size_t i = 0; i < 9; i++) {
+        r ^= ((b >> (8 - i)) & 1) * a;
+        a = step(1, Q, a);
+    }
+    return r;
+}
+
+/* Reverse an 18-bit number x */
+static fec_gf_t reverse18(fec_gf_t x) {
+    fec_gf_t ret = 0;
+    for (size_t i = 0; i < 18; i++) {
+        ret ^= ((x >> i) & 1) << (17 - i);
+    }
+    return ret;
+}
+
+/* Correct data to have the given FEC */
+void PQCLEAN_MAMABEAR_CLEAN_melas_fec_correct (
+    uint8_t *data,
+    size_t len,
+    const uint8_t fec[MELAS_FEC_BYTES]
+) {
+
+    fec_gf_t a = s18update(syndrome18(data, len), fec, MELAS_FEC_BYTES);
+    fec_gf_t c, r, htr;
+    size_t i;
+    const uint8_t table[9] = {36, 10, 43, 215, 52, 11, 116, 244, 0};
+    fec_gf_t e0, e1;
+
+    /* Form a quadratic equation from the syndrome */
+    c = mul(step(9, Q, a), step(9, Q, reverse18(a)));
+    for (i = 0, r = 0x100; i < 510; i++) {
+        r = mul(r, c);
+    }
+    r = step(17, Q, r);
+    a = step(511 - (len + MELAS_FEC_BYTES) * 8, Q, a);
+
+    /* Solve using the half trace */
+    for (i = 0, htr = 0; i < 9; i++) {
+        htr ^= ((r >> i) & 1) * table[i];
+    }
+    e0 = mul(a, htr);
+    e1 = e0 ^ a;
+
+    /* Correct the errors using the locators */
+    for (i = 0; i < len; i++) {
+        data[i] ^= (uint8_t)(e0 & (((e0 & (e0 - 1)) - 1) >> 9));
+        data[i] ^= (uint8_t)(e1 & (((e1 & (e1 - 1)) - 1) >> 9));
+        e0 = step(8, Q, e0);
+        e1 = step(8, Q, e1);
+    }
+}
diff --git a/crypto_kem/mamabear/clean/melas_fec.h b/crypto_kem/mamabear/clean/melas_fec.h
new file mode 100644
index 00000000..410ec288
--- /dev/null
+++ b/crypto_kem/mamabear/clean/melas_fec.h
@@ -0,0 +1,26 @@
+#ifndef __THREEBEARS_MELAS_FEC_H__
+#define __THREEBEARS_MELAS_FEC_H__
+
+#include "api.h"
+
+#define MELAS_FEC_BYTES 3
+#define MELAS_FEC_BITS 18
+
+typedef uint32_t fec_gf_t;
+static const fec_gf_t Q = 0x211;
+
+/* Append 3 bytes of FEC(data) to data, so that the FEC becomes 0 */
+void PQCLEAN_MAMABEAR_CLEAN_melas_fec_set(
+    uint8_t out[MELAS_FEC_BYTES],
+    const uint8_t *data,
+    size_t len
+);
+
+/* Append 3 bytes of FEC(data) to data, so that the FEC becomes 0 */
+void PQCLEAN_MAMABEAR_CLEAN_melas_fec_correct(
+    uint8_t *data,
+    size_t len,
+    const uint8_t fec[MELAS_FEC_BYTES]
+);
+
+#endif
diff --git a/crypto_kem/mamabear/clean/params.h b/crypto_kem/mamabear/clean/params.h
new file mode 100644
index 00000000..7b875af9
--- /dev/null
+++ b/crypto_kem/mamabear/clean/params.h
@@ -0,0 +1,29 @@
+#ifndef __THREEBEARS_PARAMS_H__
+#define __THREEBEARS_PARAMS_H__
+
+#define VERSION              1
+#define MATRIX_SEED_BYTES    24
+#define ENC_SEED_BYTES       32
+#define IV_BYTES             0
+#define LGX                  10
+#define DIGITS               312
+#define DIM                  3
+#define VAR_TIMES_128        52
+#define LPR_BITS             4
+#define FEC_BITS             18
+#define CCA                  1
+#define SHARED_SECRET_BYTES  32
+#define PRIVATE_KEY_BYTES    40
+#define PRF_KEY_BYTES        PRIVATE_KEY_BYTES
+
+#define BEAR_NAME   "MamaBear"
+#define encapsulate MamaBear_encapsulate
+#define decapsulate MamaBear_decapsulate
+#define get_pubkey  MamaBear_get_pubkey
+
+#define GF_BYTES ((LGX*DIGITS+7)/8)
+#define PUBLIC_KEY_BYTES (MATRIX_SEED_BYTES + DIM*GF_BYTES)
+#define CAPSULE_BYTES \
+    (DIM*GF_BYTES + IV_BYTES + ((ENC_SEED_BYTES*8+FEC_BITS)*LPR_BITS+7)/8)
+
+#endif
diff --git a/crypto_kem/mamabear/clean/ring.c b/crypto_kem/mamabear/clean/ring.c
new file mode 100644
index 00000000..d744b09e
--- /dev/null
+++ b/crypto_kem/mamabear/clean/ring.c
@@ -0,0 +1,102 @@
+/** Ring arithmetic implementation */
+#include "ring.h"
+
+/** Multiply and accumulate c += a*b */
+void PQCLEAN_MAMABEAR_CLEAN_mac(gf_t c, const gf_t a, const gf_t b) {
+    /* Reference non-Karatsuba MAC */
+    dslimb_t accum[2 * DIGITS] = {0};
+    dslimb_t chain;
+    size_t i, j;
+
+    /* Initialize accumulator = unclarify(c) */
+    for (i = 0; i < DIGITS; i++) {
+        accum[i + DIGITS / 2] = c[i];
+    }
+
+    /* Multiply */
+    for (i = 0; i < DIGITS; i++) {
+        for (j = 0; j < DIGITS; j++) {
+            accum[i + j] += (dslimb_t)a[i] * b[j];
+        }
+    }
+
+    /* Clarify and reduce */
+    for (i = 0; i < DIGITS / 2; i++) {
+        accum[i + DIGITS / 2] -= accum[i];
+        accum[i + DIGITS]   += accum[i];
+        accum[i + DIGITS / 2] += accum[i + 3 * DIGITS / 2];
+        accum[i + DIGITS]   += accum[i + 3 * DIGITS / 2];
+    }
+
+    /* Carry propagate */
+    chain = accum[3 * DIGITS / 2 - 1];
+    accum[3 * DIGITS / 2 - 1] = chain & LMASK;
+    chain >>= LGX;
+    accum[DIGITS] += chain;
+    for (i = DIGITS / 2; i < 3 * DIGITS / 2; i++) {
+        chain += accum[i];
+        c[i - DIGITS / 2] = chain & LMASK;
+        chain >>= LGX;
+    }
+    c[0] = (limb_t) (c[0] + chain);
+    c[DIGITS / 2] = (limb_t) (c[DIGITS / 2] + chain);
+}
+
+/** Reduce a gf_t to canonical form, i.e. strictly less than N. */
+void PQCLEAN_MAMABEAR_CLEAN_canon(gf_t c) {
+    const limb_t DELTA = (limb_t)1 << (LGX - 1);
+    slimb_t hi;
+    dslimb_t scarry;
+    dlimb_t carry;
+
+    /* Reduce to 0..2p */
+    hi = (slimb_t) (c[DIGITS - 1] - DELTA);
+    c[DIGITS - 1] = (limb_t) ((hi & LMASK) + DELTA);
+    c[DIGITS / 2] = (limb_t) (c[DIGITS / 2] + (hi >> LGX));
+
+    /* Strong reduce.  First subtract modulus */
+    scarry = hi >> LGX;
+    for (size_t i = 0; i < DIGITS; i++) {
+        scarry = scarry + (slimb_t)c[i] - modulus(i);
+        c[i] = scarry & LMASK;
+        scarry >>= LGX;
+    }
+
+    /* add it back */
+    carry = 0;
+    for (size_t i = 0; i < DIGITS; i++) {
+        carry = carry + c[i] + ((dlimb_t)scarry & modulus(i));
+        c[i] = carry & LMASK;
+        carry >>= LGX;
+    }
+}
+
+/** Serialize a gf_t to bytes */
+void PQCLEAN_MAMABEAR_CLEAN_contract(uint8_t ch[GF_BYTES], gf_t a) {
+    size_t pos;
+
+    PQCLEAN_MAMABEAR_CLEAN_canon(a);
+    for (size_t i = 0; i < GF_BYTES; i++) {
+        pos = (i * 8) / LGX;
+        ch[i] = (uint8_t)(a[pos] >> ((i * 8) % LGX));
+        if (i < GF_BYTES - 1) {
+            ch[i] |= (uint8_t)(a[pos + 1] << (LGX - ((i * 8) % LGX)));
+        }
+    }
+}
+
+/** Deserialize a gf_t from bytes */
+void PQCLEAN_MAMABEAR_CLEAN_expand(gf_t ll, const uint8_t ch[GF_BYTES]) {
+    limb_t tmp, buffer = 0;
+
+    for (size_t i = 0, j = 0, bbits = 0; i < GF_BYTES; i++) {
+        tmp = ch[i];
+        buffer |= (limb_t)(tmp << bbits);
+        bbits += 8;
+        if (bbits >= LGX) {
+            ll[j++] = buffer & LMASK;
+            buffer = (limb_t)(tmp >> (LGX - (bbits - 8)));
+            bbits = bbits - LGX;
+        }
+    }
+}
diff --git a/crypto_kem/mamabear/clean/ring.h b/crypto_kem/mamabear/clean/ring.h
new file mode 100644
index 00000000..3e8b1dd1
--- /dev/null
+++ b/crypto_kem/mamabear/clean/ring.h
@@ -0,0 +1,31 @@
+#ifndef __THREEBEARS_RING_H__
+#define __THREEBEARS_RING_H__
+
+#include "api.h"
+#include "params.h"
+
+typedef uint16_t limb_t;
+typedef int16_t slimb_t;
+typedef uint32_t dlimb_t;
+typedef int32_t dslimb_t;
+#define LMASK (((limb_t)1<<LGX)-1)
+typedef limb_t gf_t[DIGITS];
+
+/* Serialize a gf_t */
+void PQCLEAN_MAMABEAR_CLEAN_contract(uint8_t ch[GF_BYTES], gf_t a);
+
+/* Deserialize a gf_t */
+void PQCLEAN_MAMABEAR_CLEAN_expand(gf_t ll, const uint8_t ch[GF_BYTES]);
+
+/* Multiply and accumulate c = c + a*b */
+void PQCLEAN_MAMABEAR_CLEAN_mac(gf_t c, const gf_t a, const gf_t b);
+
+/* Reduce ring element to canonical form */
+void PQCLEAN_MAMABEAR_CLEAN_canon(gf_t c);
+
+/** Return the i'th limb of the modulus */
+static inline limb_t modulus(size_t i) {
+    return (i == DIGITS / 2) ? LMASK - 1 : LMASK;
+}
+
+#endif
diff --git a/crypto_kem/mamabear/clean/threebears.c b/crypto_kem/mamabear/clean/threebears.c
new file mode 100644
index 00000000..0aba57be
--- /dev/null
+++ b/crypto_kem/mamabear/clean/threebears.c
@@ -0,0 +1,225 @@
+/** ThreeBears reference implementation */
+#include "api.h"
+#include "melas_fec.h"
+#include "params.h"
+#include "ring.h"
+#include "sp800-185.h"
+#include "threebears.h"
+
+#define FEC_BYTES ((FEC_BITS+7)/8)
+#define ENC_BITS  (ENC_SEED_BYTES*8 + FEC_BITS)
+
+enum { HASH_PURPOSE_UNIFORM = 0, HASH_PURPOSE_KEYGEN = 1, HASH_PURPOSE_ENCAPS = 2, HASH_PURPOSE_PRF = 3 };
+
+/** Initialize the hash function with a given purpose */
+static void threebears_hash_init(
+    shake256incctx *ctx,
+    uint8_t purpose
+) {
+    const unsigned char S[] = "ThreeBears";
+    const uint8_t pblock[15] = {
+        VERSION, PRIVATE_KEY_BYTES, MATRIX_SEED_BYTES, ENC_SEED_BYTES,
+        IV_BYTES, SHARED_SECRET_BYTES, LGX, DIGITS & 0xFF, DIGITS >> 8, DIM,
+                VAR_TIMES_128 - 1, LPR_BITS, FEC_BITS, CCA, 0 /* padding */
+    };
+
+    cshake256_inc_init(ctx, NULL, 0, (const uint8_t *)S, sizeof(S) - 1);
+    cshake256_inc_absorb(ctx, (const uint8_t *)pblock, sizeof(pblock));
+    cshake256_inc_absorb(ctx, &purpose, 1);
+}
+
+/** Sample n gf_t's uniformly from a seed */
+static void uniform(gf_t matrix, const uint8_t *seed, uint8_t iv) {
+    uint8_t c[GF_BYTES];
+    shake256incctx ctx;
+
+    threebears_hash_init(&ctx, HASH_PURPOSE_UNIFORM);
+    cshake256_inc_absorb(&ctx, seed, MATRIX_SEED_BYTES);
+    cshake256_inc_absorb(&ctx, &iv, 1);
+    cshake256_inc_finalize(&ctx);
+    cshake256_inc_squeeze(c, sizeof(c), &ctx);
+    PQCLEAN_MAMABEAR_CLEAN_expand(matrix, c);
+}
+
+/** The ThreeBears error distribution */
+static slimb_t psi(uint8_t ci) {
+    int sample = 0, var = VAR_TIMES_128;
+
+    for (; var > 64; var -= 64, ci = (uint8_t)(ci << 2)) {
+        sample += ((ci + 64) >> 8) + ((ci - 64) >> 8);
+    }
+    return (slimb_t)(sample + ((ci + var) >> 8) + ((ci - var) >> 8));
+}
+
+/** Sample a vector of n noise elements */
+static void noise(gf_t x, const shake256incctx *ctx, uint8_t iv) {
+    uint8_t c[DIGITS];
+    shake256incctx ctx2;
+
+    memcpy(&ctx2, ctx, sizeof(ctx2));
+    cshake256_inc_absorb(&ctx2, &iv, 1);
+    cshake256_inc_finalize(&ctx2);
+    cshake256_inc_squeeze(c, DIGITS, &ctx2);
+    for (size_t i = 0; i < DIGITS; i++) {
+        x[i] = (limb_t)(psi(c[i]) + modulus(i));
+    }
+}
+
+/* Expand public key from private key */
+void PQCLEAN_MAMABEAR_CLEAN_get_pubkey(uint8_t *pk, const uint8_t *sk) {
+    shake256incctx ctx;
+    shake256incctx ctx2;
+    gf_t sk_expanded[DIM], b, c;
+
+    threebears_hash_init(&ctx, HASH_PURPOSE_KEYGEN);
+    cshake256_inc_absorb(&ctx, sk, PRIVATE_KEY_BYTES);
+
+    memcpy(&ctx2, &ctx, sizeof(ctx2));
+    cshake256_inc_finalize(&ctx2);
+    cshake256_inc_squeeze(pk, MATRIX_SEED_BYTES, &ctx2);
+
+    for (uint8_t i = 0; i < DIM; i++) {
+        noise(sk_expanded[i], &ctx, i);
+    }
+    for (uint8_t i = 0; i < DIM; i++) {
+        noise(c, &ctx, (uint8_t)(i + DIM));
+        for (uint8_t j = 0; j < DIM; j++) {
+            uniform(b, pk, (uint8_t) (i + DIM * j));
+            PQCLEAN_MAMABEAR_CLEAN_mac(c, b, sk_expanded[j]);
+        }
+        PQCLEAN_MAMABEAR_CLEAN_contract(&pk[MATRIX_SEED_BYTES + i * GF_BYTES], c);
+    }
+}
+
+/* Encapsulate a shared secret and return it */
+void PQCLEAN_MAMABEAR_CLEAN_encapsulate(
+    uint8_t *shared_secret,
+    uint8_t *capsule,
+    const uint8_t *pk,
+    const uint8_t *seed
+) {
+    uint8_t *lpr_data = &capsule[GF_BYTES * DIM];
+    shake256incctx ctx;
+    gf_t sk_expanded[DIM], b, c;
+    uint8_t tbi[ENC_SEED_BYTES + FEC_BYTES];
+    dlimb_t rlimb0, rlimb1;
+    limb_t h;
+    uint8_t *iv = &lpr_data[(ENC_BITS * LPR_BITS + 7) / 8];
+
+    memcpy(iv, &seed[ENC_SEED_BYTES], IV_BYTES);
+
+    threebears_hash_init(&ctx, HASH_PURPOSE_ENCAPS);
+    cshake256_inc_absorb(&ctx, pk, MATRIX_SEED_BYTES);
+    cshake256_inc_absorb(&ctx, seed, ENC_SEED_BYTES + IV_BYTES);
+
+    for (uint8_t i = 0; i < DIM; i++) {
+        noise(sk_expanded[i], &ctx, i);
+    }
+    for (uint8_t i = 0; i < DIM; i++) {
+        noise(c, &ctx, (uint8_t)(i + DIM));
+        for (uint8_t j = 0; j < DIM; j++) {
+            uniform(b, pk, (uint8_t)(j + DIM * i));
+            PQCLEAN_MAMABEAR_CLEAN_mac(c, b, sk_expanded[j]);
+        }
+        PQCLEAN_MAMABEAR_CLEAN_contract(&capsule[i * GF_BYTES], c);
+    }
+    noise(c, &ctx, (uint8_t)(2 * DIM));
+
+    /* Calculate approximate shared secret */
+    for (uint8_t i = 0; i < DIM; i++) {
+        PQCLEAN_MAMABEAR_CLEAN_expand(b, &pk[MATRIX_SEED_BYTES + i * GF_BYTES]);
+        PQCLEAN_MAMABEAR_CLEAN_mac(c, b, sk_expanded[i]);
+    }
+    PQCLEAN_MAMABEAR_CLEAN_canon(c);
+
+
+    memcpy(tbi, seed, ENC_SEED_BYTES);
+
+    PQCLEAN_MAMABEAR_CLEAN_melas_fec_set(&tbi[ENC_SEED_BYTES], tbi, ENC_SEED_BYTES);
+
+    /* Export with rounding */
+    for (size_t i = 0; i < ENC_BITS; i += 2) {
+        h = (limb_t)(tbi[i / 8] >> (i % 8));
+        rlimb0 = (dlimb_t)((c[i / 2]          >> (LGX - LPR_BITS)) + (h << 3));
+        rlimb1 = (dlimb_t)((c[DIGITS - i / 2 - 1] >> (LGX - LPR_BITS)) + ((h >> 1) << 3));
+        lpr_data[i / 2] = (uint8_t)((rlimb0 & 0xF) | rlimb1 << 4);
+    }
+
+    cshake256_inc_finalize(&ctx);
+    cshake256_inc_squeeze(shared_secret, SHARED_SECRET_BYTES, &ctx);
+}
+
+/* Decapsulate a shared secret and return it */
+void PQCLEAN_MAMABEAR_CLEAN_decapsulate(
+    uint8_t shared_secret[SHARED_SECRET_BYTES],
+    const uint8_t capsule[CAPSULE_BYTES],
+    const uint8_t sk[PRIVATE_KEY_BYTES]
+) {
+    const uint8_t *lpr_data = &capsule[GF_BYTES * DIM];
+    shake256incctx ctx;
+    gf_t ska, b, c = {0};
+    uint8_t seed[ENC_SEED_BYTES + FEC_BYTES + IV_BYTES];
+    limb_t rounding, out;
+    size_t j;
+    limb_t our_rlimb, their_rlimb, delta;
+    uint8_t pk[PUBLIC_KEY_BYTES], capsule2[CAPSULE_BYTES];
+    uint8_t ret, ok, sep, prfk[PRF_KEY_BYTES];
+    uint8_t prfout[SHARED_SECRET_BYTES];
+
+    /* Calculate approximate shared secret */
+    threebears_hash_init(&ctx, HASH_PURPOSE_KEYGEN);
+    cshake256_inc_absorb(&ctx, sk, PRIVATE_KEY_BYTES);
+
+    for (uint8_t i = 0; i < DIM; i++) {
+        PQCLEAN_MAMABEAR_CLEAN_expand(b, &capsule[i * GF_BYTES]);
+        noise(ska, &ctx, i);
+        PQCLEAN_MAMABEAR_CLEAN_mac(c, ska, b);
+    }
+
+    /* Recover seed from LPR data */
+    PQCLEAN_MAMABEAR_CLEAN_canon(c);
+    rounding = 1 << (LPR_BITS - 1);
+    out = 0;
+    for (int32_t i = ENC_BITS - 1; i >= 0; i--) {
+        j = (size_t) ((i & 1) ? DIGITS - i / 2 - 1 : i / 2);
+        our_rlimb = (limb_t)(c[j] >> (LGX - LPR_BITS - 1));
+        their_rlimb = (limb_t)(lpr_data[i * LPR_BITS / 8] >> ((i * LPR_BITS) % 8));
+        delta =  (limb_t)(their_rlimb * 2 - our_rlimb + rounding);
+        out |= (limb_t)(((delta >> LPR_BITS) & 1) << (i % 8));
+        if (i % 8 == 0) {
+            seed[i / 8] = (uint8_t)out;
+            out = 0;
+        }
+    }
+    PQCLEAN_MAMABEAR_CLEAN_melas_fec_correct(seed, ENC_SEED_BYTES, &seed[ENC_SEED_BYTES]);
+
+    /* Re-encapsulate and check; encapsulate will compute the shared secret */
+    //pk[PUBLIC_KEY_BYTES], capsule2[CAPSULE_BYTES];
+    PQCLEAN_MAMABEAR_CLEAN_get_pubkey(pk, sk);
+    memcpy(&seed[ENC_SEED_BYTES], &lpr_data[(ENC_BITS * LPR_BITS + 7) / 8], IV_BYTES);
+    PQCLEAN_MAMABEAR_CLEAN_encapsulate(shared_secret, capsule2, pk, seed);
+
+    /* Check capsule == capsule2 in constant time */
+    ret = 0;
+    for (size_t i = 0; i < CAPSULE_BYTES; i++) {
+        ret |= capsule[i] ^ capsule2[i];
+    }
+    ok = (uint8_t)(((int)ret - 1) >> 8);
+
+    /* Calculate PRF key */
+    sep = 0xFF;
+    cshake256_inc_absorb(&ctx, &sep, 1);
+    cshake256_inc_finalize(&ctx);
+    cshake256_inc_squeeze(prfk, PRF_KEY_BYTES, &ctx);
+
+    /* Calculate PRF */
+    threebears_hash_init(&ctx, HASH_PURPOSE_PRF);
+    cshake256_inc_absorb(&ctx, prfk, PRF_KEY_BYTES);
+    cshake256_inc_absorb(&ctx, capsule, CAPSULE_BYTES);
+    cshake256_inc_finalize(&ctx);
+    cshake256_inc_squeeze(prfout, SHARED_SECRET_BYTES, &ctx);
+
+    for (size_t i = 0; i < SHARED_SECRET_BYTES; i++) {
+        shared_secret[i] = (uint8_t)((shared_secret[i] & ok) | (prfout[i] & ~ok));
+    }
+}
diff --git a/crypto_kem/mamabear/clean/threebears.h b/crypto_kem/mamabear/clean/threebears.h
new file mode 100644
index 00000000..0d979068
--- /dev/null
+++ b/crypto_kem/mamabear/clean/threebears.h
@@ -0,0 +1,60 @@
+#ifndef __THREE_BEARS_MAMABEAR_H__
+#define __THREE_BEARS_MAMABEAR_H__
+
+#include <stddef.h> /* for size_t */
+#include <stdint.h>
+
+#define MAMABEAR_KEYGEN_SEED_BYTES 40
+#define MAMABEAR_PRIVATE_KEY_BYTES MAMABEAR_KEYGEN_SEED_BYTES
+#define MAMABEAR_SHARED_SECRET_BYTES 32
+#define MAMABEAR_ENC_SEED_AND_IV_BYTES 32
+#define MAMABEAR_PUBLIC_KEY_BYTES 1194
+#define MAMABEAR_CAPSULE_BYTES 1307
+
+/**
+ * Expand a secret seed to a public/private keypair.
+ *
+ * @param[out] pk The public key.
+ * @param[in] sk The private key, which must be uniformly random.
+ */
+void MamaBear_get_pubkey (
+    uint8_t pk[MAMABEAR_PUBLIC_KEY_BYTES],
+    const uint8_t sk[MAMABEAR_PRIVATE_KEY_BYTES]
+);
+
+/**
+ * Create a shared secret using a random seed and another party's public key.
+ *
+ * Input and output parameters may not alias.
+ *
+ * @param[out] shared_secret The shared secret key.
+ * @param[out] capsule A ciphertext to send to the other party.
+ * @param[in] pk The other party's public key.
+ * @param[in] seed A random seed.
+ */
+void MamaBear_encapsulate (
+    uint8_t shared_secret[MAMABEAR_SHARED_SECRET_BYTES],
+    uint8_t capsule[MAMABEAR_CAPSULE_BYTES],
+    const uint8_t pk[MAMABEAR_PUBLIC_KEY_BYTES],
+    const uint8_t seed[MAMABEAR_ENC_SEED_AND_IV_BYTES]
+);
+
+/**
+ * Extract the shared secret from a capsule using the private key.
+ * Has a negligible but nonzero probability of failure.
+ *
+ * Input and output parameters may not alias.
+ *
+ * @param[out] shared_secret The shared secret.
+ * @param[in] capsule The capsule produced by encapsulate_cca2.
+ * @param[in] sk The private key.
+ */
+void MamaBear_decapsulate (
+    uint8_t shared_secret[MAMABEAR_SHARED_SECRET_BYTES],
+    const uint8_t capsule[MAMABEAR_CAPSULE_BYTES],
+    const uint8_t sk[MAMABEAR_PRIVATE_KEY_BYTES]
+);
+
+void PQCLEAN_MAMABEAR_CLEAN_secure_bzero (void *s, size_t size);
+
+#endif
diff --git a/crypto_kem/papabear/META.yml b/crypto_kem/papabear/META.yml
new file mode 100644
index 00000000..8dbe6cf3
--- /dev/null
+++ b/crypto_kem/papabear/META.yml
@@ -0,0 +1,15 @@
+name: PapaBear
+type: kem
+claimed-nist-level: 5
+claimed-security: IND-CCA2
+length-public-key: 1584 
+length-ciphertext: 1697
+length-secret-key: 40
+length-shared-secret: 32
+nistkat-sha256: 977429507fa60a24a608193a507e39f4d9deaf4c6359f94f36b2d9ca0897c997 
+principal-submitters:
+  - Mike Hamburg
+implementations:
+    - name: clean
+      version: round2 
+
diff --git a/crypto_kem/papabear/clean/LICENSE b/crypto_kem/papabear/clean/LICENSE
new file mode 100644
index 00000000..5fb15a7c
--- /dev/null
+++ b/crypto_kem/papabear/clean/LICENSE
@@ -0,0 +1,24 @@
+Copyright (c) 2016-2019 Rambus, Inc.
+and licensed under the following MIT license.
+
+The MIT License (MIT)
+
+Copyright (c) 2016-2019 Rambus Inc.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
diff --git a/crypto_kem/papabear/clean/Makefile b/crypto_kem/papabear/clean/Makefile
new file mode 100644
index 00000000..f11aefe7
--- /dev/null
+++ b/crypto_kem/papabear/clean/Makefile
@@ -0,0 +1,21 @@
+# This Makefile can be used with GNU Make or BSD Make
+
+LIB=libpapabear_clean.a
+
+HEADERS = api.h melas_fec.h params.h ring.h threebears.h
+OBJECTS = kem.o melas_fec.o ring.o threebears.o 
+
+
+CFLAGS=-O3 -Wcast-align=strict -Wall -Wconversion -Wextra -Wpedantic -Wvla -Wmissing-prototypes -Wredundant-decls -std=c99 -I../../../common $(EXTRAFLAGS)
+
+all: $(LIB)
+
+%.o: %.c $(HEADERS)
+	$(CC) $(CFLAGS) -c -o $@ $<
+
+$(LIB): $(OBJECTS)
+	$(AR) -r $@ $(OBJECTS)
+
+clean:
+	$(RM) $(OBJECTS)
+	$(RM) $(LIB)
diff --git a/crypto_kem/papabear/clean/Makefile.Microsoft_nmake b/crypto_kem/papabear/clean/Makefile.Microsoft_nmake
new file mode 100644
index 00000000..87462c40
--- /dev/null
+++ b/crypto_kem/papabear/clean/Makefile.Microsoft_nmake
@@ -0,0 +1,19 @@
+# This Makefile can be used with Microsoft Visual Studio's nmake using the command:
+#    nmake /f Makefile.Microsoft_nmake
+
+LIBRARY=libpapabear_clean.lib
+OBJECTS = kem.obj melas_fec.obj ring.obj threebears.obj
+
+CFLAGS=/nologo /I ..\..\..\common /W4 /WX
+
+all: $(LIBRARY)
+
+# Make sure objects are recompiled if headers change.
+$(OBJECTS): *.h
+
+$(LIBRARY): $(OBJECTS)
+	LIB.EXE /NOLOGO /WX /OUT:$@ $**
+
+clean:
+    -DEL $(OBJECTS)
+    -DEL $(LIBRARY)
diff --git a/crypto_kem/papabear/clean/api.h b/crypto_kem/papabear/clean/api.h
new file mode 100644
index 00000000..c872e00c
--- /dev/null
+++ b/crypto_kem/papabear/clean/api.h
@@ -0,0 +1,18 @@
+#ifndef PQCLEAN_PAPABEAR_CLEAN_API_H
+#define PQCLEAN_PAPABEAR_CLEAN_API_H
+
+#include <stddef.h>
+#include <stdint.h>
+#include <string.h>
+
+#define PQCLEAN_PAPABEAR_CLEAN_CRYPTO_SECRETKEYBYTES 40
+#define PQCLEAN_PAPABEAR_CLEAN_CRYPTO_PUBLICKEYBYTES 1584
+#define PQCLEAN_PAPABEAR_CLEAN_CRYPTO_BYTES 32
+#define PQCLEAN_PAPABEAR_CLEAN_CRYPTO_CIPHERTEXTBYTES 1697
+#define PQCLEAN_PAPABEAR_CLEAN_CRYPTO_ALGNAME "PapaBear"
+
+int PQCLEAN_PAPABEAR_CLEAN_crypto_kem_keypair(uint8_t *pk, uint8_t *sk);
+int PQCLEAN_PAPABEAR_CLEAN_crypto_kem_enc(uint8_t *ct, uint8_t *ss, const uint8_t *pk);
+int PQCLEAN_PAPABEAR_CLEAN_crypto_kem_dec(uint8_t *ss, const uint8_t *ct, const uint8_t *sk);
+
+#endif
diff --git a/crypto_kem/papabear/clean/kem.c b/crypto_kem/papabear/clean/kem.c
new file mode 100644
index 00000000..908d3118
--- /dev/null
+++ b/crypto_kem/papabear/clean/kem.c
@@ -0,0 +1,22 @@
+#include "api.h"
+#include "params.h"
+#include "randombytes.h"
+#include "threebears.h"
+
+int PQCLEAN_PAPABEAR_CLEAN_crypto_kem_keypair(uint8_t *pk, uint8_t *sk) {
+    randombytes(sk, PRIVATE_KEY_BYTES);
+    PQCLEAN_PAPABEAR_CLEAN_get_pubkey(pk, sk);
+    return 0;
+}
+
+int PQCLEAN_PAPABEAR_CLEAN_crypto_kem_enc(uint8_t *ct, uint8_t *ss, const uint8_t *pk) {
+    uint8_t seed[ENC_SEED_BYTES + IV_BYTES];
+    randombytes(seed, sizeof(seed));
+    encapsulate(ss, ct, pk, seed);
+    return 0;
+}
+
+int PQCLEAN_PAPABEAR_CLEAN_crypto_kem_dec(uint8_t *ss, const uint8_t *ct, const uint8_t *sk) {
+    PQCLEAN_PAPABEAR_CLEAN_decapsulate(ss, ct, sk);
+    return 0;
+}
diff --git a/crypto_kem/papabear/clean/melas_fec.c b/crypto_kem/papabear/clean/melas_fec.c
new file mode 100644
index 00000000..2e271067
--- /dev/null
+++ b/crypto_kem/papabear/clean/melas_fec.c
@@ -0,0 +1,87 @@
+/* Melas forward error correction, reference code (as implemented in the paper) */
+#include "melas_fec.h"
+
+/* Return s/2^n mod R */
+static fec_gf_t step(size_t n, fec_gf_t R, fec_gf_t s) {
+    for (; n; n--) {
+        s = (s ^ ((s & 1) * R)) >> 1;
+    }
+    return s;
+}
+
+/* Compute syndrome(data), where data has length len */
+#define syndrome18(data,len) s18update(0,data,len)
+static fec_gf_t s18update(fec_gf_t r, const uint8_t *data, size_t len) {
+    for (size_t i = 0; i < len; i++) {
+        r = step(8, 0x46231, r ^ data[i]);
+    }
+    return r;
+}
+
+/* Append 3 bytes of FEC(data) to data, so that the FEC becomes 0 */
+void PQCLEAN_PAPABEAR_CLEAN_melas_fec_set(
+    uint8_t out[MELAS_FEC_BYTES],
+    const uint8_t *data,
+    size_t len
+) {
+    fec_gf_t fec = syndrome18(data, len);
+    for (size_t i = 0; i < MELAS_FEC_BYTES; i++, fec >>= 8) {
+        out[i] = (uint8_t)fec;
+    }
+}
+
+/* Return a*b mod Q */
+static fec_gf_t mul(fec_gf_t a, fec_gf_t b) {
+    fec_gf_t r = 0;
+    for (size_t i = 0; i < 9; i++) {
+        r ^= ((b >> (8 - i)) & 1) * a;
+        a = step(1, Q, a);
+    }
+    return r;
+}
+
+/* Reverse an 18-bit number x */
+static fec_gf_t reverse18(fec_gf_t x) {
+    fec_gf_t ret = 0;
+    for (size_t i = 0; i < 18; i++) {
+        ret ^= ((x >> i) & 1) << (17 - i);
+    }
+    return ret;
+}
+
+/* Correct data to have the given FEC */
+void PQCLEAN_PAPABEAR_CLEAN_melas_fec_correct (
+    uint8_t *data,
+    size_t len,
+    const uint8_t fec[MELAS_FEC_BYTES]
+) {
+
+    fec_gf_t a = s18update(syndrome18(data, len), fec, MELAS_FEC_BYTES);
+    fec_gf_t c, r, htr;
+    size_t i;
+    const uint8_t table[9] = {36, 10, 43, 215, 52, 11, 116, 244, 0};
+    fec_gf_t e0, e1;
+
+    /* Form a quadratic equation from the syndrome */
+    c = mul(step(9, Q, a), step(9, Q, reverse18(a)));
+    for (i = 0, r = 0x100; i < 510; i++) {
+        r = mul(r, c);
+    }
+    r = step(17, Q, r);
+    a = step(511 - (len + MELAS_FEC_BYTES) * 8, Q, a);
+
+    /* Solve using the half trace */
+    for (i = 0, htr = 0; i < 9; i++) {
+        htr ^= ((r >> i) & 1) * table[i];
+    }
+    e0 = mul(a, htr);
+    e1 = e0 ^ a;
+
+    /* Correct the errors using the locators */
+    for (i = 0; i < len; i++) {
+        data[i] ^= (uint8_t)(e0 & (((e0 & (e0 - 1)) - 1) >> 9));
+        data[i] ^= (uint8_t)(e1 & (((e1 & (e1 - 1)) - 1) >> 9));
+        e0 = step(8, Q, e0);
+        e1 = step(8, Q, e1);
+    }
+}
diff --git a/crypto_kem/papabear/clean/melas_fec.h b/crypto_kem/papabear/clean/melas_fec.h
new file mode 100644
index 00000000..6d2ca1ee
--- /dev/null
+++ b/crypto_kem/papabear/clean/melas_fec.h
@@ -0,0 +1,26 @@
+#ifndef __THREEBEARS_MELAS_FEC_H__
+#define __THREEBEARS_MELAS_FEC_H__
+
+#include "api.h"
+
+#define MELAS_FEC_BYTES 3
+#define MELAS_FEC_BITS 18
+
+typedef uint32_t fec_gf_t;
+static const fec_gf_t Q = 0x211;
+
+/* Append 3 bytes of FEC(data) to data, so that the FEC becomes 0 */
+void PQCLEAN_PAPABEAR_CLEAN_melas_fec_set(
+    uint8_t out[MELAS_FEC_BYTES],
+    const uint8_t *data,
+    size_t len
+);
+
+/* Append 3 bytes of FEC(data) to data, so that the FEC becomes 0 */
+void PQCLEAN_PAPABEAR_CLEAN_melas_fec_correct(
+    uint8_t *data,
+    size_t len,
+    const uint8_t fec[MELAS_FEC_BYTES]
+);
+
+#endif
diff --git a/crypto_kem/papabear/clean/params.h b/crypto_kem/papabear/clean/params.h
new file mode 100644
index 00000000..7d601cc5
--- /dev/null
+++ b/crypto_kem/papabear/clean/params.h
@@ -0,0 +1,29 @@
+#ifndef __THREEBEARS_PARAMS_H__
+#define __THREEBEARS_PARAMS_H__
+
+#define VERSION              1
+#define MATRIX_SEED_BYTES    24
+#define ENC_SEED_BYTES       32
+#define IV_BYTES             0
+#define LGX                  10
+#define DIGITS               312
+#define DIM                  4
+#define VAR_TIMES_128        40
+#define LPR_BITS             4
+#define FEC_BITS             18
+#define CCA                  1
+#define SHARED_SECRET_BYTES  32
+#define PRIVATE_KEY_BYTES    40
+#define PRF_KEY_BYTES        PRIVATE_KEY_BYTES
+
+#define BEAR_NAME   "PapaBear"
+#define encapsulate PapaBear_encapsulate
+#define decapsulate PapaBear_decapsulate
+#define get_pubkey  PapaBear_get_pubkey
+
+#define GF_BYTES ((LGX*DIGITS+7)/8)
+#define PUBLIC_KEY_BYTES (MATRIX_SEED_BYTES + DIM*GF_BYTES)
+#define CAPSULE_BYTES \
+    (DIM*GF_BYTES + IV_BYTES + ((ENC_SEED_BYTES*8+FEC_BITS)*LPR_BITS+7)/8)
+
+#endif
diff --git a/crypto_kem/papabear/clean/ring.c b/crypto_kem/papabear/clean/ring.c
new file mode 100644
index 00000000..a770260b
--- /dev/null
+++ b/crypto_kem/papabear/clean/ring.c
@@ -0,0 +1,102 @@
+/** Ring arithmetic implementation */
+#include "ring.h"
+
+/** Multiply and accumulate c += a*b */
+void PQCLEAN_PAPABEAR_CLEAN_mac(gf_t c, const gf_t a, const gf_t b) {
+    /* Reference non-Karatsuba MAC */
+    dslimb_t accum[2 * DIGITS] = {0};
+    dslimb_t chain;
+    size_t i, j;
+
+    /* Initialize accumulator = unclarify(c) */
+    for (i = 0; i < DIGITS; i++) {
+        accum[i + DIGITS / 2] = c[i];
+    }
+
+    /* Multiply */
+    for (i = 0; i < DIGITS; i++) {
+        for (j = 0; j < DIGITS; j++) {
+            accum[i + j] += (dslimb_t)a[i] * b[j];
+        }
+    }
+
+    /* Clarify and reduce */
+    for (i = 0; i < DIGITS / 2; i++) {
+        accum[i + DIGITS / 2] -= accum[i];
+        accum[i + DIGITS]   += accum[i];
+        accum[i + DIGITS / 2] += accum[i + 3 * DIGITS / 2];
+        accum[i + DIGITS]   += accum[i + 3 * DIGITS / 2];
+    }
+
+    /* Carry propagate */
+    chain = accum[3 * DIGITS / 2 - 1];
+    accum[3 * DIGITS / 2 - 1] = chain & LMASK;
+    chain >>= LGX;
+    accum[DIGITS] += chain;
+    for (i = DIGITS / 2; i < 3 * DIGITS / 2; i++) {
+        chain += accum[i];
+        c[i - DIGITS / 2] = chain & LMASK;
+        chain >>= LGX;
+    }
+    c[0] = (limb_t) (c[0] + chain);
+    c[DIGITS / 2] = (limb_t) (c[DIGITS / 2] + chain);
+}
+
+/** Reduce a gf_t to canonical form, i.e. strictly less than N. */
+void PQCLEAN_PAPABEAR_CLEAN_canon(gf_t c) {
+    const limb_t DELTA = (limb_t)1 << (LGX - 1);
+    slimb_t hi;
+    dslimb_t scarry;
+    dlimb_t carry;
+
+    /* Reduce to 0..2p */
+    hi = (slimb_t) (c[DIGITS - 1] - DELTA);
+    c[DIGITS - 1] = (limb_t) ((hi & LMASK) + DELTA);
+    c[DIGITS / 2] = (limb_t) (c[DIGITS / 2] + (hi >> LGX));
+
+    /* Strong reduce.  First subtract modulus */
+    scarry = hi >> LGX;
+    for (size_t i = 0; i < DIGITS; i++) {
+        scarry = scarry + (slimb_t)c[i] - modulus(i);
+        c[i] = scarry & LMASK;
+        scarry >>= LGX;
+    }
+
+    /* add it back */
+    carry = 0;
+    for (size_t i = 0; i < DIGITS; i++) {
+        carry = carry + c[i] + ((dlimb_t)scarry & modulus(i));
+        c[i] = carry & LMASK;
+        carry >>= LGX;
+    }
+}
+
+/** Serialize a gf_t to bytes */
+void PQCLEAN_PAPABEAR_CLEAN_contract(uint8_t ch[GF_BYTES], gf_t a) {
+    size_t pos;
+
+    PQCLEAN_PAPABEAR_CLEAN_canon(a);
+    for (size_t i = 0; i < GF_BYTES; i++) {
+        pos = (i * 8) / LGX;
+        ch[i] = (uint8_t)(a[pos] >> ((i * 8) % LGX));
+        if (i < GF_BYTES - 1) {
+            ch[i] |= (uint8_t)(a[pos + 1] << (LGX - ((i * 8) % LGX)));
+        }
+    }
+}
+
+/** Deserialize a gf_t from bytes */
+void PQCLEAN_PAPABEAR_CLEAN_expand(gf_t ll, const uint8_t ch[GF_BYTES]) {
+    limb_t tmp, buffer = 0;
+
+    for (size_t i = 0, j = 0, bbits = 0; i < GF_BYTES; i++) {
+        tmp = ch[i];
+        buffer |= (limb_t)(tmp << bbits);
+        bbits += 8;
+        if (bbits >= LGX) {
+            ll[j++] = buffer & LMASK;
+            buffer = (limb_t)(tmp >> (LGX - (bbits - 8)));
+            bbits = bbits - LGX;
+        }
+    }
+}
diff --git a/crypto_kem/papabear/clean/ring.h b/crypto_kem/papabear/clean/ring.h
new file mode 100644
index 00000000..aac7f750
--- /dev/null
+++ b/crypto_kem/papabear/clean/ring.h
@@ -0,0 +1,31 @@
+#ifndef __THREEBEARS_RING_H__
+#define __THREEBEARS_RING_H__
+
+#include "api.h"
+#include "params.h"
+
+typedef uint16_t limb_t;
+typedef int16_t slimb_t;
+typedef uint32_t dlimb_t;
+typedef int32_t dslimb_t;
+#define LMASK (((limb_t)1<<LGX)-1)
+typedef limb_t gf_t[DIGITS];
+
+/* Serialize a gf_t */
+void PQCLEAN_PAPABEAR_CLEAN_contract(uint8_t ch[GF_BYTES], gf_t a);
+
+/* Deserialize a gf_t */
+void PQCLEAN_PAPABEAR_CLEAN_expand(gf_t ll, const uint8_t ch[GF_BYTES]);
+
+/* Multiply and accumulate c = c + a*b */
+void PQCLEAN_PAPABEAR_CLEAN_mac(gf_t c, const gf_t a, const gf_t b);
+
+/* Reduce ring element to canonical form */
+void PQCLEAN_PAPABEAR_CLEAN_canon(gf_t c);
+
+/** Return the i'th limb of the modulus */
+static inline limb_t modulus(size_t i) {
+    return (i == DIGITS / 2) ? LMASK - 1 : LMASK;
+}
+
+#endif
diff --git a/crypto_kem/papabear/clean/threebears.c b/crypto_kem/papabear/clean/threebears.c
new file mode 100644
index 00000000..9cf69be5
--- /dev/null
+++ b/crypto_kem/papabear/clean/threebears.c
@@ -0,0 +1,225 @@
+/** ThreeBears reference implementation */
+#include "api.h"
+#include "melas_fec.h"
+#include "params.h"
+#include "ring.h"
+#include "sp800-185.h"
+#include "threebears.h"
+
+#define FEC_BYTES ((FEC_BITS+7)/8)
+#define ENC_BITS  (ENC_SEED_BYTES*8 + FEC_BITS)
+
+enum { HASH_PURPOSE_UNIFORM = 0, HASH_PURPOSE_KEYGEN = 1, HASH_PURPOSE_ENCAPS = 2, HASH_PURPOSE_PRF = 3 };
+
+/** Initialize the hash function with a given purpose */
+static void threebears_hash_init(
+    shake256incctx *ctx,
+    uint8_t purpose
+) {
+    const unsigned char S[] = "ThreeBears";
+    const uint8_t pblock[15] = {
+        VERSION, PRIVATE_KEY_BYTES, MATRIX_SEED_BYTES, ENC_SEED_BYTES,
+        IV_BYTES, SHARED_SECRET_BYTES, LGX, DIGITS & 0xFF, DIGITS >> 8, DIM,
+                VAR_TIMES_128 - 1, LPR_BITS, FEC_BITS, CCA, 0 /* padding */
+    };
+
+    cshake256_inc_init(ctx, NULL, 0, (const uint8_t *)S, sizeof(S) - 1);
+    cshake256_inc_absorb(ctx, (const uint8_t *)pblock, sizeof(pblock));
+    cshake256_inc_absorb(ctx, &purpose, 1);
+}
+
+/** Sample n gf_t's uniformly from a seed */
+static void uniform(gf_t matrix, const uint8_t *seed, uint8_t iv) {
+    uint8_t c[GF_BYTES];
+    shake256incctx ctx;
+
+    threebears_hash_init(&ctx, HASH_PURPOSE_UNIFORM);
+    cshake256_inc_absorb(&ctx, seed, MATRIX_SEED_BYTES);
+    cshake256_inc_absorb(&ctx, &iv, 1);
+    cshake256_inc_finalize(&ctx);
+    cshake256_inc_squeeze(c, sizeof(c), &ctx);
+    PQCLEAN_PAPABEAR_CLEAN_expand(matrix, c);
+}
+
+/** The ThreeBears error distribution */
+static slimb_t psi(uint8_t ci) {
+    int sample = 0, var = VAR_TIMES_128;
+
+    for (; var > 64; var -= 64, ci = (uint8_t)(ci << 2)) {
+        sample += ((ci + 64) >> 8) + ((ci - 64) >> 8);
+    }
+    return (slimb_t)(sample + ((ci + var) >> 8) + ((ci - var) >> 8));
+}
+
+/** Sample a vector of n noise elements */
+static void noise(gf_t x, const shake256incctx *ctx, uint8_t iv) {
+    uint8_t c[DIGITS];
+    shake256incctx ctx2;
+
+    memcpy(&ctx2, ctx, sizeof(ctx2));
+    cshake256_inc_absorb(&ctx2, &iv, 1);
+    cshake256_inc_finalize(&ctx2);
+    cshake256_inc_squeeze(c, DIGITS, &ctx2);
+    for (size_t i = 0; i < DIGITS; i++) {
+        x[i] = (limb_t)(psi(c[i]) + modulus(i));
+    }
+}
+
+/* Expand public key from private key */
+void PQCLEAN_PAPABEAR_CLEAN_get_pubkey(uint8_t *pk, const uint8_t *sk) {
+    shake256incctx ctx;
+    shake256incctx ctx2;
+    gf_t sk_expanded[DIM], b, c;
+
+    threebears_hash_init(&ctx, HASH_PURPOSE_KEYGEN);
+    cshake256_inc_absorb(&ctx, sk, PRIVATE_KEY_BYTES);
+
+    memcpy(&ctx2, &ctx, sizeof(ctx2));
+    cshake256_inc_finalize(&ctx2);
+    cshake256_inc_squeeze(pk, MATRIX_SEED_BYTES, &ctx2);
+
+    for (uint8_t i = 0; i < DIM; i++) {
+        noise(sk_expanded[i], &ctx, i);
+    }
+    for (uint8_t i = 0; i < DIM; i++) {
+        noise(c, &ctx, (uint8_t)(i + DIM));
+        for (uint8_t j = 0; j < DIM; j++) {
+            uniform(b, pk, (uint8_t) (i + DIM * j));
+            PQCLEAN_PAPABEAR_CLEAN_mac(c, b, sk_expanded[j]);
+        }
+        PQCLEAN_PAPABEAR_CLEAN_contract(&pk[MATRIX_SEED_BYTES + i * GF_BYTES], c);
+    }
+}
+
+/* Encapsulate a shared secret and return it */
+void PQCLEAN_PAPABEAR_CLEAN_encapsulate(
+    uint8_t *shared_secret,
+    uint8_t *capsule,
+    const uint8_t *pk,
+    const uint8_t *seed
+) {
+    uint8_t *lpr_data = &capsule[GF_BYTES * DIM];
+    shake256incctx ctx;
+    gf_t sk_expanded[DIM], b, c;
+    uint8_t tbi[ENC_SEED_BYTES + FEC_BYTES];
+    dlimb_t rlimb0, rlimb1;
+    limb_t h;
+    uint8_t *iv = &lpr_data[(ENC_BITS * LPR_BITS + 7) / 8];
+
+    memcpy(iv, &seed[ENC_SEED_BYTES], IV_BYTES);
+
+    threebears_hash_init(&ctx, HASH_PURPOSE_ENCAPS);
+    cshake256_inc_absorb(&ctx, pk, MATRIX_SEED_BYTES);
+    cshake256_inc_absorb(&ctx, seed, ENC_SEED_BYTES + IV_BYTES);
+
+    for (uint8_t i = 0; i < DIM; i++) {
+        noise(sk_expanded[i], &ctx, i);
+    }
+    for (uint8_t i = 0; i < DIM; i++) {
+        noise(c, &ctx, (uint8_t)(i + DIM));
+        for (uint8_t j = 0; j < DIM; j++) {
+            uniform(b, pk, (uint8_t)(j + DIM * i));
+            PQCLEAN_PAPABEAR_CLEAN_mac(c, b, sk_expanded[j]);
+        }
+        PQCLEAN_PAPABEAR_CLEAN_contract(&capsule[i * GF_BYTES], c);
+    }
+    noise(c, &ctx, (uint8_t)(2 * DIM));
+
+    /* Calculate approximate shared secret */
+    for (uint8_t i = 0; i < DIM; i++) {
+        PQCLEAN_PAPABEAR_CLEAN_expand(b, &pk[MATRIX_SEED_BYTES + i * GF_BYTES]);
+        PQCLEAN_PAPABEAR_CLEAN_mac(c, b, sk_expanded[i]);
+    }
+    PQCLEAN_PAPABEAR_CLEAN_canon(c);
+
+
+    memcpy(tbi, seed, ENC_SEED_BYTES);
+
+    PQCLEAN_PAPABEAR_CLEAN_melas_fec_set(&tbi[ENC_SEED_BYTES], tbi, ENC_SEED_BYTES);
+
+    /* Export with rounding */
+    for (size_t i = 0; i < ENC_BITS; i += 2) {
+        h = (limb_t)(tbi[i / 8] >> (i % 8));
+        rlimb0 = (dlimb_t)((c[i / 2]          >> (LGX - LPR_BITS)) + (h << 3));
+        rlimb1 = (dlimb_t)((c[DIGITS - i / 2 - 1] >> (LGX - LPR_BITS)) + ((h >> 1) << 3));
+        lpr_data[i / 2] = (uint8_t)((rlimb0 & 0xF) | rlimb1 << 4);
+    }
+
+    cshake256_inc_finalize(&ctx);
+    cshake256_inc_squeeze(shared_secret, SHARED_SECRET_BYTES, &ctx);
+}
+
+/* Decapsulate a shared secret and return it */
+void PQCLEAN_PAPABEAR_CLEAN_decapsulate(
+    uint8_t shared_secret[SHARED_SECRET_BYTES],
+    const uint8_t capsule[CAPSULE_BYTES],
+    const uint8_t sk[PRIVATE_KEY_BYTES]
+) {
+    const uint8_t *lpr_data = &capsule[GF_BYTES * DIM];
+    shake256incctx ctx;
+    gf_t ska, b, c = {0};
+    uint8_t seed[ENC_SEED_BYTES + FEC_BYTES + IV_BYTES];
+    limb_t rounding, out;
+    size_t j;
+    limb_t our_rlimb, their_rlimb, delta;
+    uint8_t pk[PUBLIC_KEY_BYTES], capsule2[CAPSULE_BYTES];
+    uint8_t ret, ok, sep, prfk[PRF_KEY_BYTES];
+    uint8_t prfout[SHARED_SECRET_BYTES];
+
+    /* Calculate approximate shared secret */
+    threebears_hash_init(&ctx, HASH_PURPOSE_KEYGEN);
+    cshake256_inc_absorb(&ctx, sk, PRIVATE_KEY_BYTES);
+
+    for (uint8_t i = 0; i < DIM; i++) {
+        PQCLEAN_PAPABEAR_CLEAN_expand(b, &capsule[i * GF_BYTES]);
+        noise(ska, &ctx, i);
+        PQCLEAN_PAPABEAR_CLEAN_mac(c, ska, b);
+    }
+
+    /* Recover seed from LPR data */
+    PQCLEAN_PAPABEAR_CLEAN_canon(c);
+    rounding = 1 << (LPR_BITS - 1);
+    out = 0;
+    for (int32_t i = ENC_BITS - 1; i >= 0; i--) {
+        j = (size_t) ((i & 1) ? DIGITS - i / 2 - 1 : i / 2);
+        our_rlimb = (limb_t)(c[j] >> (LGX - LPR_BITS - 1));
+        their_rlimb = (limb_t)(lpr_data[i * LPR_BITS / 8] >> ((i * LPR_BITS) % 8));
+        delta =  (limb_t)(their_rlimb * 2 - our_rlimb + rounding);
+        out |= (limb_t)(((delta >> LPR_BITS) & 1) << (i % 8));
+        if (i % 8 == 0) {
+            seed[i / 8] = (uint8_t)out;
+            out = 0;
+        }
+    }
+    PQCLEAN_PAPABEAR_CLEAN_melas_fec_correct(seed, ENC_SEED_BYTES, &seed[ENC_SEED_BYTES]);
+
+    /* Re-encapsulate and check; encapsulate will compute the shared secret */
+    //pk[PUBLIC_KEY_BYTES], capsule2[CAPSULE_BYTES];
+    PQCLEAN_PAPABEAR_CLEAN_get_pubkey(pk, sk);
+    memcpy(&seed[ENC_SEED_BYTES], &lpr_data[(ENC_BITS * LPR_BITS + 7) / 8], IV_BYTES);
+    PQCLEAN_PAPABEAR_CLEAN_encapsulate(shared_secret, capsule2, pk, seed);
+
+    /* Check capsule == capsule2 in constant time */
+    ret = 0;
+    for (size_t i = 0; i < CAPSULE_BYTES; i++) {
+        ret |= capsule[i] ^ capsule2[i];
+    }
+    ok = (uint8_t)(((int)ret - 1) >> 8);
+
+    /* Calculate PRF key */
+    sep = 0xFF;
+    cshake256_inc_absorb(&ctx, &sep, 1);
+    cshake256_inc_finalize(&ctx);
+    cshake256_inc_squeeze(prfk, PRF_KEY_BYTES, &ctx);
+
+    /* Calculate PRF */
+    threebears_hash_init(&ctx, HASH_PURPOSE_PRF);
+    cshake256_inc_absorb(&ctx, prfk, PRF_KEY_BYTES);
+    cshake256_inc_absorb(&ctx, capsule, CAPSULE_BYTES);
+    cshake256_inc_finalize(&ctx);
+    cshake256_inc_squeeze(prfout, SHARED_SECRET_BYTES, &ctx);
+
+    for (size_t i = 0; i < SHARED_SECRET_BYTES; i++) {
+        shared_secret[i] = (uint8_t)((shared_secret[i] & ok) | (prfout[i] & ~ok));
+    }
+}
diff --git a/crypto_kem/papabear/clean/threebears.h b/crypto_kem/papabear/clean/threebears.h
new file mode 100644
index 00000000..d4378696
--- /dev/null
+++ b/crypto_kem/papabear/clean/threebears.h
@@ -0,0 +1,60 @@
+#ifndef __THREE_BEARS_PAPABEAR_H__
+#define __THREE_BEARS_PAPABEAR_H__
+
+#include <stddef.h> /* for size_t */
+#include <stdint.h>
+
+#define PAPABEAR_KEYGEN_SEED_BYTES 40
+#define PAPABEAR_PRIVATE_KEY_BYTES PAPABEAR_KEYGEN_SEED_BYTES
+#define PAPABEAR_SHARED_SECRET_BYTES 32
+#define PAPABEAR_ENC_SEED_AND_IV_BYTES 32
+#define PAPABEAR_PUBLIC_KEY_BYTES 1584
+#define PAPABEAR_CAPSULE_BYTES 1697
+
+/**
+ * Expand a secret seed to a public/private keypair.
+ *
+ * @param[out] pk The public key.
+ * @param[in] sk The private key, which must be uniformly random.
+ */
+void PapaBear_get_pubkey (
+    uint8_t pk[PAPABEAR_PUBLIC_KEY_BYTES],
+    const uint8_t sk[PAPABEAR_PRIVATE_KEY_BYTES]
+);
+
+/**
+ * Create a shared secret using a random seed and another party's public key.
+ *
+ * Input and output parameters may not alias.
+ *
+ * @param[out] shared_secret The shared secret key.
+ * @param[out] capsule A ciphertext to send to the other party.
+ * @param[in] pk The other party's public key.
+ * @param[in] seed A random seed.
+ */
+void PapaBear_encapsulate (
+    uint8_t shared_secret[PAPABEAR_SHARED_SECRET_BYTES],
+    uint8_t capsule[PAPABEAR_CAPSULE_BYTES],
+    const uint8_t pk[PAPABEAR_PUBLIC_KEY_BYTES],
+    const uint8_t seed[PAPABEAR_ENC_SEED_AND_IV_BYTES]
+);
+
+/**
+ * Extract the shared secret from a capsule using the private key.
+ * Has a negligible but nonzero probability of failure.
+ *
+ * Input and output parameters may not alias.
+ *
+ * @param[out] shared_secret The shared secret.
+ * @param[in] capsule The capsule produced by encapsulate_cca2.
+ * @param[in] sk The private key.
+ */
+void PapaBear_decapsulate (
+    uint8_t shared_secret[PAPABEAR_SHARED_SECRET_BYTES],
+    const uint8_t capsule[PAPABEAR_CAPSULE_BYTES],
+    const uint8_t sk[PAPABEAR_PRIVATE_KEY_BYTES]
+);
+
+void PQCLEAN_PAPABEAR_CLEAN_secure_bzero (void *s, size_t size);
+
+#endif