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#include <string.h>
#include "crypto_sign.h"
#include "crypto_hash_sha512.h"
#include "ge.h"
#include "sc.h"
#include "zeroize.h"
#include "crypto_additions.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 */
/* Erase any traces of private scalar or
nonce left in the stack from sc_muladd */
zeroize_stack();
zeroize(nonce, 64);
return 0;
}
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