diff --git a/sha3.c b/sha3.c
index 931ae02..e359707 100644
--- a/sha3.c
+++ b/sha3.c
@@ -1,12 +1,36 @@
 // sha3.c
 // 19-Nov-11  Markku-Juhani O. Saarinen <mjos@iki.fi>
+// 22-May-25  Kris Kwiatkowski <kris@amongbytes.com>
 
 // Revised 07-Aug-15 to match with official release of FIPS PUB 202 "SHA3"
 // Revised 03-Sep-15 for portability + OpenSSL - style API
+// Revised 22-May-25 Added bit-interleaved implementation optimized for 32-bit architectures.
 
 #include "sha3.h"
 
-// update the state with given number of rounds
+// Interleave even and odd bits into one 64-bit line
+uint64_t unshuffle(uint32_t even, uint32_t odd) {
+    uint64_t result = 0;
+    for (int i = 0; i < 32; i++) {
+        result |= ((uint64_t)(even >> i) & 1) << (2 * i);
+        result |= ((uint64_t)(odd  >> i) & 1) << (2 * i + 1);
+    }
+    return result;
+}
+
+uint32_t shuffle_even(uint64_t x) {
+    x &= 0x5555555555555555ULL;
+    x = (x | (x >> 1)) & 0x3333333333333333ULL;
+    x = (x | (x >> 2)) & 0x0F0F0F0F0F0F0F0FULL;
+    x = (x | (x >> 4)) & 0x00FF00FF00FF00FFULL;
+    x = (x | (x >> 8)) & 0x0000FFFF0000FFFFULL;
+    x = (x | (x >> 16)) & 0x00000000FFFFFFFFULL;
+    return (uint32_t)x;
+}
+
+uint32_t shuffle_odd(uint64_t x) {
+    return shuffle_even(x >> 1);
+}
 
 void sha3_keccakf(uint64_t st[25])
 {
@@ -32,7 +56,9 @@ void sha3_keccakf(uint64_t st[25])
 
     // variables
     int i, j, r;
-    uint64_t t, bc[5];
+    uint32_t t1, t2;
+    uint32_t even[25], odd[25];
+    uint32_t bc_even[5], bc_odd[5];
 
 #if __BYTE_ORDER__ != __ORDER_LITTLE_ENDIAN__
     uint8_t *v;
@@ -47,38 +73,73 @@ void sha3_keccakf(uint64_t st[25])
     }
 #endif
 
+    for (i = 0; i < 25; i++) {
+        even[i] = shuffle_even(st[i]);
+        odd[i] = shuffle_odd(st[i]);;
+    }
+
     // actual iteration
     for (r = 0; r < KECCAKF_ROUNDS; r++) {
-
         // Theta
-        for (i = 0; i < 5; i++)
-            bc[i] = st[i] ^ st[i + 5] ^ st[i + 10] ^ st[i + 15] ^ st[i + 20];
-
         for (i = 0; i < 5; i++) {
-            t = bc[(i + 4) % 5] ^ ROTL64(bc[(i + 1) % 5], 1);
-            for (j = 0; j < 25; j += 5)
-                st[j + i] ^= t;
+            bc_even[i] = even[i] ^ even[i + 5] ^ even[i + 10] ^ even[i + 15] ^ even[i + 20];
+            bc_odd[i] = odd[i] ^ odd[i + 5] ^ odd[i + 10] ^ odd[i + 15] ^ odd[i + 20];
+        }
+
+        // Chi
+        for (i = 0; i < 5; i++) {
+
+            uint32_t rot32 = ROTL32(bc_odd[(i + 1) % 5], 1);
+            t1 = bc_even[(i + 4) % 5] ^ rot32;
+            t2 = bc_odd[(i + 4) % 5] ^ bc_even[(i + 1) % 5];
+
+            for (j = 0; j < 25; j += 5) {
+                even[j + i] ^= t1;
+                odd[j + i] ^= t2;
+            }
         }
 
         // Rho Pi
-        t = st[1];
+        t1 = even[1]; t2 = odd[1];
         for (i = 0; i < 24; i++) {
             j = keccakf_piln[i];
-            bc[0] = st[j];
-            st[j] = ROTL64(t, keccakf_rotc[i]);
-            t = bc[0];
+            bc_even[0] = even[j]; bc_odd[0] = odd[j];
+
+            int half = keccakf_rotc[i] >> 1;
+            if (keccakf_rotc[i]&1) {
+                // U0 = ROT32(U1, tau)
+                odd[j] = ROTL32(t1, half);
+                // U1 = ROT32(U0, tau + 1)
+                even[j] = ROTL32(t2, half + 1);
+            } else {
+                // U0 = ROT32(U0, tau)
+                odd[j] = ROTL32(t2, half);
+                // U1 = ROT32(U1, tau)
+                even[j] = ROTL32(t1, half);
+            }
+
+            t1 = bc_even[0]; t2 = bc_odd[0];
         }
 
         //  Chi
         for (j = 0; j < 25; j += 5) {
-            for (i = 0; i < 5; i++)
-                bc[i] = st[j + i];
-            for (i = 0; i < 5; i++)
-                st[j + i] ^= (~bc[(i + 1) % 5]) & bc[(i + 2) % 5];
+            for (i = 0; i < 5; i++) {
+                bc_even[i] = even[j + i];
+                bc_odd[i] = odd[j + i];
+            }
+            for (i = 0; i < 5; i++) {
+                even[j + i] ^= (~bc_even[(i + 1) % 5]) & bc_even[(i + 2) % 5];
+                odd[j + i] ^= (~bc_odd[(i + 1) % 5]) & bc_odd[(i + 2) % 5];
+            }
         }
 
-        //  Iota
-        st[0] ^= keccakf_rndc[r];
+        //  Iota (can be precomputed)
+        even[0] ^= shuffle_even(keccakf_rndc[r]);
+        odd[0] ^= shuffle_odd(keccakf_rndc[r]);
+    }
+
+    for (i = 0; i < 25; i++) {
+        st[i] = unshuffle(even[i], odd[i]);
     }
 
 #if __BYTE_ORDER__ != __ORDER_LITTLE_ENDIAN__
diff --git a/sha3.h b/sha3.h
index ba24f43..c75adf0 100644
--- a/sha3.h
+++ b/sha3.h
@@ -15,6 +15,10 @@
 #define ROTL64(x, y) (((x) << (y)) | ((x) >> (64 - (y))))
 #endif
 
+#ifndef ROTL32
+#define ROTL32(x, y) (((x) << (y)) | ((x) >> (32 - (y))))
+#endif
+
 // state context
 typedef struct {
     union {                                 // state: