ed25519/open.c
Orson Peters 7da894b006 changes
2013-01-10 21:24:49 +01:00

40 lines
890 B
C

#include "ed25519.h"
#include "sha512.h"
#include "ge.h"
#include "sc.h"
int ed25519_sign_open(
unsigned char *m,unsigned long long *mlen,
const unsigned char *sm,unsigned long long smlen,
const unsigned char *pk
)
{
unsigned char h[64];
unsigned char checkr[32];
ge_p3 A;
ge_p2 R;
unsigned long long i;
*mlen = -1;
if (smlen < 64) return -1;
if (sm[63] & 224) return -1;
if (ge_frombytes_negate_vartime(&A,pk) != 0) return -1;
for (i = 0;i < smlen;++i) m[i] = sm[i];
for (i = 0;i < 32;++i) m[32 + i] = pk[i];
sha512(h,m,smlen);
sc_reduce(h);
ge_double_scalarmult_vartime(&R,h,&A,sm + 32);
ge_tobytes(checkr,&R);
if (crypto_verify_32(checkr,sm) != 0) {
for (i = 0;i < smlen;++i) m[i] = 0;
return -1;
}
for (i = 0;i < smlen - 64;++i) m[i] = sm[64 + i];
for (i = smlen - 64;i < smlen;++i) m[i] = 0;
*mlen = smlen - 64;
return 0;
}