1 files changed, 47 insertions, 0 deletions
diff --git a/jni/ed25519/additions/sign_modified.c b/jni/ed25519/additions/sign_modified.c
new file mode 100644
index 00000000..61332e70
--- /dev/null
+++ b/jni/ed25519/additions/sign_modified.c
@@ -0,0 +1,47 @@
+#include <string.h>
+#include "crypto_sign.h"
+#include "crypto_hash_sha512.h"
+#include "ge.h"
+#include "sc.h"
+#include "zeroize.h"
+
+/* NEW: Compare to pristine crypto_sign() 
+   Uses explicit private key for nonce derivation and as scalar,
+   instead of deriving both from a master key.
+*/
+int crypto_sign_modified(
+  unsigned char *sm,
+  const unsigned char *m,unsigned long long mlen,
+  const unsigned char *sk, const unsigned char* pk,
+  const unsigned char* random
+)
+{
+  unsigned char nonce[64];
+  unsigned char hram[64];
+  ge_p3 R;
+  int count=0;
+
+  memmove(sm + 64,m,mlen);
+  memmove(sm + 32,sk,32); /* NEW: Use privkey directly for nonce derivation */
+
+  /* NEW : add prefix to separate hash uses - see .h */
+  sm[0] = 0xFE;
+  for (count = 1; count < 32; count++)
+    sm[count] = 0xFF;
+
+  /* NEW: add suffix of random data */
+  memmove(sm + mlen + 64, random, 64);
+
+  crypto_hash_sha512(nonce,sm,mlen + 128);
+  memmove(sm + 32,pk,32);
+
+  sc_reduce(nonce);
+  ge_scalarmult_base(&R,nonce);
+  ge_p3_tobytes(sm,&R);
+
+  crypto_hash_sha512(hram,sm,mlen + 64);
+  sc_reduce(hram);
+  sc_muladd(sm + 32,hram,sk,nonce); /* NEW: Use privkey directly */
+
+  return 0;
+}