diff --git a/hash.c b/hash.c
index 7d043f3..d574921 100644
--- a/hash.c
+++ b/hash.c
@@ -101,12 +101,12 @@ int hash_2n_n(unsigned char *out,const unsigned char *in, const unsigned char *p
   
   SET_KEY_BIT(addr,1);
   SET_BLOCK_BIT(addr,0);
-  prg_with_counter(key, n, pub_seed, n, addr);
+  prg_with_counter(key, pub_seed, n, addr);
   SET_KEY_BIT(addr,0);
   // Use MSB order
-  prg_with_counter(bitmask, n, pub_seed, n, addr);
+  prg_with_counter(bitmask, pub_seed, n, addr);
   SET_BLOCK_BIT(addr,1);
-  prg_with_counter(bitmask+n, n, pub_seed, n, addr);
+  prg_with_counter(bitmask+n, pub_seed, n, addr);
   for(i=0;i<n;i++)
   {
     buf[i] = 0x00;
@@ -136,9 +136,9 @@ int hash_n_n(unsigned char *out,const unsigned char *in, const unsigned char *pu
   int i;
   
   WOTS_SELECT_KEY(addr);
-  prg_with_counter(key, n, pub_seed, n, addr);
+  prg_with_counter(key, pub_seed, n, addr);
   WOTS_SELECT_BLOCK(addr);
-  prg_with_counter(bitmask, n, pub_seed, n, addr);
+  prg_with_counter(bitmask, pub_seed, n, addr);
   for(i=0;i<n;i++)
   {
     buf[i] = 0x00;
diff --git a/prg.c b/prg.c
index 6aa6ac6..acb790e 100644
--- a/prg.c
+++ b/prg.c
@@ -6,7 +6,9 @@ Public domain.
 #include "chacha.h"
 #include "prg.h"
 #include <stdio.h>
-
+#include <openssl/sha.h>
+#include <openssl/hmac.h>
+#include <openssl/evp.h>
 
 const unsigned char zero_nonce[12] = {0};
 
@@ -15,18 +17,50 @@ const unsigned char zero_nonce[12] = {0};
  */
 void prg(unsigned char *r, unsigned long long rlen, const unsigned char *key, unsigned int key_len)
 {  
-  CRYPTO_chacha_20_keystream(r, rlen, key, zero_nonce, 0);
+  if(key_len == 32){
+    CRYPTO_chacha_20_keystream(r, rlen, key, zero_nonce, 0);
+  }
+  else
+  {
+    if(key_len == 64)
+    {
+      unsigned long long left = rlen;
+      u_int32_t counter = 0;
+      unsigned char *c = (unsigned char*)&counter;
+      unsigned int length;
+      unsigned int i = 0; 
+      unsigned char tmp[64];
+      while(left > 0)
+      {
+	HMAC(EVP_sha512(), key, key_len, c , 4, tmp, &length);
+	if(length != 64)
+	  {
+	    fprintf(stderr, "HMAC outputs %d bytes... That should not happen...",length); 
+	  }
+	for(i = 0; ((i < length) && (i < left));i++)
+	{
+	  r[rlen-left+i] = tmp[i];
+	}
+	left -=length;
+	counter++;
+      }
+    }
+    else {
+      fprintf(stderr,"prg.c:: Code only supports 32 byte and 64 byte seeds");
+    }
+  }
 }
 
 /**
- * Generates rlen output bytes using ChaCha20.
- * Nonce and counter are set depending on the address addr.
+ * Generates n output bytes using ChaCha20 (n=32) or HMAC-SHA2-512 (n=64).
+ * 
+ * For ChaCha, nonce and counter are set depending on the address addr. For HMAC, addr is used as message.
  */
-void prg_with_counter(unsigned char *r, unsigned long long rlen, const unsigned char *key, unsigned int key_len, const unsigned char addr[16])
+void prg_with_counter(unsigned char *r, const unsigned char *key, unsigned int n, const unsigned char addr[16])
 {
   int i;
   unsigned char nonce[12];
-  if(key_len == 32){
+  if(n == 32){
     for(i = 0; i < 12; i++)
     {
       nonce[i] = addr[i];
@@ -34,20 +68,26 @@ void prg_with_counter(unsigned char *r, unsigned long long rlen, const unsigned
     uint32_t counter;
     counter = (((uint32_t)addr[12]) << 24)|(((uint32_t)addr[13]) << 16)|(((uint32_t)addr[14]) << 8)|addr[15];
     // TODO: Check address handling. Endianess?
-    CRYPTO_chacha_20_keystream(r, rlen, key, nonce, counter);
+    CRYPTO_chacha_20_keystream(r, n, key, nonce, counter);
   } 
   else 
   {
-    if(key_len == 64)
+    if(n == 64)
     {
-      for(i = 0; i < 12; i++)
+//       for(i = 0; i < 12; i++)
+//       {
+// 	nonce[i] = addr[i];
+//       }
+//       uint32_t counter;
+//       counter = (((uint32_t)addr[12]) << 24)|(((uint32_t)addr[13]) << 16)|(((uint32_t)addr[14]) << 8)|addr[15];
+//       // TODO: WRONG! Uses only 32 byte of key. However, does not compile with HMAC-SHA512
+//       CRYPTO_chacha_20_keystream(r, rlen, key, nonce, counter);
+      unsigned int length;
+      HMAC(EVP_sha512(), key, n, addr, 16, r, &length);
+      if(length != 64)
       {
-	nonce[i] = addr[i];
+	fprintf(stderr, "HMAC outputs %d bytes... That should not happen...",length); 
       }
-      uint32_t counter;
-      counter = (((uint32_t)addr[12]) << 24)|(((uint32_t)addr[13]) << 16)|(((uint32_t)addr[14]) << 8)|addr[15];
-      // TODO: WRONG! Uses only 32 byte of key. However, does not compile with HMAC-SHA512
-      CRYPTO_chacha_20_keystream(r, rlen, key, nonce, counter);
     } else {
       fprintf(stderr,"prg.c:: Code only supports 32 byte and 64 byte seeds");
     }
diff --git a/prg.h b/prg.h
index d95c787..750414e 100644
--- a/prg.h
+++ b/prg.h
@@ -15,8 +15,8 @@ Public domain.
 void prg(unsigned char *r, unsigned long long rlen, const unsigned char *key, unsigned int key_len);
 
 /**
- * Generates rlen output bytes using key_len-byte key and hash address addr and places them in r.
+ * Generates n output bytes using n-byte key and hash address addr and places them in r.
  * 
  */
-void prg_with_counter(unsigned char *r, unsigned long long rlen, const unsigned char *key, unsigned int key_len, const unsigned char addr[16]);
+void prg_with_counter(unsigned char *r, const unsigned char *key, unsigned int n, const unsigned char addr[16]);
 #endif
diff --git a/test/test_chacha.c b/test/test_chacha.c
index 606617f..5392fdd 100644
--- a/test/test_chacha.c
+++ b/test/test_chacha.c
@@ -11,23 +11,26 @@ static void hexdump(unsigned char *a, size_t len)
 
 int main()
 {
+  int n = 32;
   unsigned char seed[32] = {0};
-  unsigned char out[64];
+//   unsigned char seed[64] = {0,0};
+  
+  unsigned char out[2*n];
   unsigned char addr[16] = {2};
 
   printf("Case 1: All 0\n");
-  prg(out, 64, seed, 32);
+  prg(out, 2*n, seed, n);
 
   printf("\n");
-  hexdump(out, 64);
+  hexdump(out, 2*n);
   printf("\n");
   
   printf("Case 2: key = 1\n");
   seed[31] = 1;
-  prg_with_counter(out, 64, seed, 32, addr);
+  prg_with_counter(out, seed, n, addr);
 
   printf("\n");
-  hexdump(out, 64);
+  hexdump(out, n);
   printf("\n");
   return 0;
 }
diff --git a/test/test_wots.c b/test/test_wots.c
index cf21b3b..794db0c 100644
--- a/test/test_wots.c
+++ b/test/test_wots.c
@@ -11,24 +11,25 @@ static void hexdump(unsigned char *a, size_t len)
 
 int main()
 {
-unsigned char seed[32];
-unsigned char pub_seed[32];
-wots_params params;
-wots_set_params(&params, 32, 32, 16);
+  int n = 32;
+  unsigned char seed[n];
+  unsigned char pub_seed[n];
+  wots_params params;
+  wots_set_params(&params, n, n, 16);
 
-int sig_len = params.len*params.n;
+  int sig_len = params.len*params.n;
 
-unsigned char pk1[sig_len];
-unsigned char pk2[sig_len];
-unsigned char sig[sig_len];
-unsigned char addr[16] = {1,2,3,4};
+  unsigned char pk1[sig_len];
+  unsigned char pk2[sig_len];
+  unsigned char sig[sig_len];
+  unsigned char addr[16] = {1,2,3,4};
 
-  unsigned char msg[32];
+  unsigned char msg[n];
   int i;
 
-  randombytes(seed, 32);
-  randombytes(pub_seed, 32);
-  randombytes(msg, 32);
+  randombytes(seed, n);
+  randombytes(pub_seed, n);
+  randombytes(msg, n);
   //randombytes(addr, 16);
 
   wots_pkgen(pk1, seed, &params, pub_seed, addr);
diff --git a/test/test_xmss.c b/test/test_xmss.c
index 46c07a6..1407b6a 100644
--- a/test/test_xmss.c
+++ b/test/test_xmss.c
@@ -7,8 +7,7 @@
 #define SIGNATURES 50
 
 
-unsigned char sk[100];
-unsigned char pk[64];
+
 unsigned char mi[MLEN];
 unsigned long long smlen;
 unsigned long long mlen;
@@ -17,13 +16,16 @@ int main()
 {
   int r;
   unsigned long long i;
-  int m = 32;
-  int n = 32;
+  int m = 64;
+  int n = 64;
   int h = 8;
   int w = 16;
   
   unsigned long errors = 0;
   
+  unsigned char sk[3*n+4];
+  unsigned char pk[2*n];
+
   xmss_params p;
   xmss_params *params = &p;
   xmss_set_params(params, m, n, h, w);
@@ -75,6 +77,7 @@ int main()
 
     /* Test with modified signature */
     /* Modified index */
+    sm[signature_length+10] ^= 1;
     sm[2] ^= 1;
     r = xmss_sign_open(mo, &mlen, sm, smlen, pk, params);
     printf("%d\n", r+1);
diff --git a/test/test_xmss_fast.c b/test/test_xmss_fast.c
index dd26167..34b5977 100644
--- a/test/test_xmss_fast.c
+++ b/test/test_xmss_fast.c
@@ -8,8 +8,7 @@
 #define SIGNATURES 256
 
 
-unsigned char sk[100];
-unsigned char pk[64];
+
 unsigned char mi[MLEN];
 unsigned long long smlen;
 unsigned long long mlen;
@@ -26,6 +25,9 @@ int main()
   
   unsigned long errors = 0;
   
+  unsigned char sk[3*n+4];
+  unsigned char pk[2*n];
+
   xmss_params p;
   xmss_params *params = &p;
   xmss_set_params(params, m, n, h, w, k);
@@ -34,7 +36,7 @@ int main()
   unsigned char stack[(h+1)*n];
   unsigned int stackoffset = 0;
   unsigned char stacklevels[h+1];
-  unsigned char auth[h*n];
+  unsigned char auth[(h)*n];
   unsigned char keep[(h >> 1)*n];
   treehash_inst treehash[h-k];
   unsigned char th_nodes[(h-k)*n];
@@ -64,7 +66,7 @@ int main()
   unsigned long idx = ((unsigned long)sk[0] << 24) | ((unsigned long)sk[1] << 16) | ((unsigned long)sk[2] << 8) | sk[3];
   if(idx) printf("\nidx != 0 %lu\n",idx);
   
-  for(i=0;i<(1<<h);i++){
+  for(i=0;i<((1<<h));i++){
     printf("sign\n");
     xmss_sign(sk, state, sm, &smlen, mi, MLEN, params);
     idx = ((unsigned long)sm[0] << 24) | ((unsigned long)sm[1] << 16) | ((unsigned long)sm[2] << 8) | sm[3];
@@ -93,6 +95,7 @@ int main()
 
     /* Test with modified signature */
     /* Modified index */
+    sm[signature_length+10] ^= 1;
     sm[2] ^= 1;
     r = xmss_sign_open(mo, &mlen, sm, smlen, pk, params);
     printf("%d\n", r+1);
diff --git a/test/test_xmssmt.c b/test/test_xmssmt.c
index b39b578..ad2a9a4 100644
--- a/test/test_xmssmt.c
+++ b/test/test_xmssmt.c
@@ -53,7 +53,7 @@ int main()
 
   if(idx) printf("\nidx != 0: %llu\n",idx);
   
-  for(i=0;i<SIGNATURES;i++){
+  for(i=0;i<(1<<h);i++){
     printf("sign\n");
     xmssmt_sign(sk, sm, &smlen, mi, MLEN, params);
     idx = 0;
diff --git a/wots.c b/wots.c
index c513413..41e3eec 100644
--- a/wots.c
+++ b/wots.c
@@ -45,7 +45,7 @@ void wots_set_params(wots_params *params, int m, int n, int w)
  */
 static void expand_seed(unsigned char *outseeds, const unsigned char *inseed, const wots_params *params)
 {
-  prg(outseeds, params->keysize, inseed, 32);
+  prg(outseeds, params->keysize, inseed, params->n);
 }
 
 /**
diff --git a/xmss.c b/xmss.c
index 0dbc733..1c77305 100644
--- a/xmss.c
+++ b/xmss.c
@@ -79,16 +79,18 @@ Public domain.
   a[12] = (a[12] & 252) | ((v >> 22) & 3);}
 
 
-  /**
+/**
  * Used for pseudorandom keygeneration,
  * generates the seed for the WOTS keypair at address addr
+ * 
+ * takes n byte sk_seed and returns n byte seed using 16 byte address addr.
  */
-static void get_seed(unsigned char seed[32], const unsigned char *sk_seed, unsigned char addr[16])
+static void get_seed(unsigned char *seed, const unsigned char *sk_seed, int n, unsigned char addr[16])
 {
   // Make sure that chain addr, hash addr, and key bit are 0!
   ZEROISE_OTS_ADDR(addr);
   // Generate pseudorandom value
-  prg_with_counter(seed, 32, sk_seed, 32, addr);
+  prg_with_counter(seed, sk_seed, n, addr);
 }
 
 /**
@@ -175,10 +177,10 @@ static void l_tree(unsigned char *leaf, unsigned char *wots_pk, const xmss_param
  */
 static void gen_leaf_wots(unsigned char *leaf, const unsigned char *sk_seed, const xmss_params *params, const unsigned char *pub_seed, unsigned char ltree_addr[16], unsigned char ots_addr[16])
 {
-  unsigned char seed[32];
+  unsigned char seed[params->n];
   unsigned char pk[params->wots_par.keysize];
 
-  get_seed(seed, sk_seed, ots_addr);
+  get_seed(seed, sk_seed, params->n, ots_addr);
   wots_pkgen(pk, seed, &(params->wots_par), pub_seed, ots_addr);
 
   l_tree(leaf, pk, params, pub_seed, ltree_addr); 
@@ -448,7 +450,7 @@ int xmss_sign(unsigned char *sk, unsigned char *sig_msg, unsigned long long *sig
   SET_OTS_ADDRESS(ots_addr,idx);
   
   // Compute seed for OTS key pair
-  get_seed(ots_seed, sk_seed, ots_addr);
+  get_seed(ots_seed, sk_seed, n, ots_addr);
      
   // Compute WOTS signature
   wots_sign(sig_msg, msg_h, ots_seed, &(params->wots_par), pub_seed, ots_addr);
@@ -673,7 +675,7 @@ int xmssmt_sign(unsigned char *sk, unsigned char *sig_msg, unsigned long long *s
   SET_OTS_ADDRESS(ots_addr, idx_leaf);
   
   // Compute seed for OTS key pair
-  get_seed(ots_seed, sk_seed, ots_addr);
+  get_seed(ots_seed, sk_seed, n, ots_addr);
      
   // Compute WOTS signature
   wots_sign(sig_msg, msg_h, ots_seed, &(params->xmss_par.wots_par), pub_seed, ots_addr);
@@ -696,7 +698,7 @@ int xmssmt_sign(unsigned char *sk, unsigned char *sig_msg, unsigned long long *s
     SET_OTS_ADDRESS(ots_addr, idx_leaf);
     
     // Compute seed for OTS key pair
-    get_seed(ots_seed, sk_seed, ots_addr);
+    get_seed(ots_seed, sk_seed, n, ots_addr);
       
     // Compute WOTS signature
     wots_sign(sig_msg, root, ots_seed, &(params->xmss_par.wots_par), pub_seed, ots_addr);
diff --git a/xmss_fast.c b/xmss_fast.c
index 62a6f48..f833029 100644
--- a/xmss_fast.c
+++ b/xmss_fast.c
@@ -78,16 +78,18 @@ Public domain.
   a[13] = (v >> 14) & 255;\
   a[12] = (a[12] & 252) | ((v >> 22) & 3);}
 
-  /**
+/**
  * Used for pseudorandom keygeneration,
  * generates the seed for the WOTS keypair at address addr
+ * 
+ * takes n byte sk_seed and returns n byte seed using 16 byte address addr.
  */
-static void get_seed(unsigned char seed[32], const unsigned char *sk_seed, unsigned char addr[16])
+static void get_seed(unsigned char *seed, const unsigned char *sk_seed, int n, unsigned char addr[16])
 {
   // Make sure that chain addr, hash addr, and key bit are 0!
   ZEROISE_OTS_ADDR(addr);
   // Generate pseudorandom value
-  prg_with_counter(seed, 32, sk_seed, 32, addr);
+  prg_with_counter(seed, sk_seed, n, addr);
 }
 
 /**
@@ -200,10 +202,10 @@ static void l_tree(unsigned char *leaf, unsigned char *wots_pk, const xmss_param
  */
 static void gen_leaf_wots(unsigned char *leaf, const unsigned char *sk_seed, const xmss_params *params, const unsigned char *pub_seed, unsigned char ltree_addr[16], unsigned char ots_addr[16])
 {
-  unsigned char seed[32];
+  unsigned char seed[params->n];
   unsigned char pk[params->wots_par.keysize];
 
-  get_seed(seed, sk_seed, ots_addr);
+  get_seed(seed, sk_seed, params->n, ots_addr);
   wots_pkgen(pk, seed, &(params->wots_par), pub_seed, ots_addr);
 
   l_tree(leaf, pk, params, pub_seed, ltree_addr); 
@@ -679,7 +681,7 @@ int xmss_sign(unsigned char *sk, bds_state *state, unsigned char *sig_msg, unsig
   SET_OTS_ADDRESS(ots_addr,idx);
   
   // Compute seed for OTS key pair
-  get_seed(ots_seed, sk_seed, ots_addr);
+  get_seed(ots_seed, sk_seed, n, ots_addr);
      
   // Compute WOTS signature
   wots_sign(sig_msg, msg_h, ots_seed, &(params->wots_par), pub_seed, ots_addr);
@@ -828,7 +830,7 @@ int xmssmt_keypair(unsigned char *pk, unsigned char *sk, bds_state *states, unsi
     // Compute seed for OTS key pair
     treehash_setup(pk, params->xmss_par.h, 0, states + i, sk+params->index_len, &(params->xmss_par), pk+n, addr);
     SET_LAYER_ADDRESS(addr, (i+1));
-    get_seed(ots_seed, sk+params->index_len, addr);
+    get_seed(ots_seed, sk+params->index_len, n, addr);
     wots_sign(wots_sigs + i*params->xmss_par.wots_par.keysize, pk, ots_seed, &(params->xmss_par.wots_par), pk+n, addr);
   }
   treehash_setup(pk, params->xmss_par.h, 0, states + i, sk+params->index_len, &(params->xmss_par), pk+n, addr);
@@ -927,7 +929,7 @@ int xmssmt_sign(unsigned char *sk, bds_state *states, unsigned char *wots_sigs,
   SET_OTS_ADDRESS(ots_addr, idx_leaf);
   
   // Compute seed for OTS key pair
-  get_seed(ots_seed, sk_seed, ots_addr);
+  get_seed(ots_seed, sk_seed, n, ots_addr);
      
   // Compute WOTS signature
   wots_sign(sig_msg, msg_h, ots_seed, &(params->xmss_par.wots_par), pub_seed, ots_addr);
@@ -974,7 +976,7 @@ int xmssmt_sign(unsigned char *sk, bds_state *states, unsigned char *wots_sigs,
         SET_OTS_ADDRESS(ots_addr, (((idx >> ((i+1) * tree_h)) + 1) & ((1 << tree_h)-1)));
         SET_LAYER_ADDRESS(ots_addr, (i+1));
 
-        get_seed(ots_seed, sk+params->index_len, ots_addr);
+        get_seed(ots_seed, sk+params->index_len, n, ots_addr);
         wots_sign(wots_sigs + i*params->xmss_par.wots_par.keysize, states[i].stack, ots_seed, &(params->xmss_par.wots_par), pub_seed, ots_addr);
 
         states[params->d + i].stackoffset = 0;