diff options
| -rw-r--r-- | src/ec25519_secret.c | 26 |
1 files changed, 11 insertions, 15 deletions
diff --git a/src/ec25519_secret.c b/src/ec25519_secret.c index b79b46c..fd703d6 100644 --- a/src/ec25519_secret.c +++ b/src/ec25519_secret.c @@ -25,8 +25,8 @@ */ /* - Simple finite field operations on the prime field F_p for - p = 2^252 + 27742317777372353535851937790883648493, which + Simple finite field operations on the prime field F_q for + q = 2^252 + 27742317777372353535851937790883648493, which is the order of the base point used for ec25519 */ @@ -152,35 +152,31 @@ void ecc_25519_secret_reduce(ecc_secret_key_256 *out, const ecc_secret_key_256 * /* Montgomery modular multiplication algorithm */ static void montgomery(unsigned char out[32], const unsigned char a[32], const unsigned char b[32]) { - unsigned int a_i; unsigned int i, j; - unsigned int r0; + unsigned int nq; unsigned int u; for (i = 0; i < 32; i++) out[i] = 0; - for (i = 0; i < 256; i++) { - a_i = a[i / 8] >> (i & 7); - a_i &= 1; - - u = out[0] + a_i*b[0]; - r0 = u & 1; - u += r0 * q[0]; + for (i = 0; i < 32; i++) { + u = out[0] + a[i]*b[0]; + nq = (u*27) & 255; + u += nq*q[0]; for (j = 1; j < 32; ++j) { - u += (out[j] + a_i*b[j] + r0*q[j]) << 8; - out[j-1] = (u >> 1) & 255; + u += (out[j] + a[i]*b[j] + nq*q[j]) << 8; u >>= 8; + out[j-1] = u; } - out[31] = u >> 1; + out[31] = u >> 8; } } void ecc_25519_secret_mult(ecc_secret_key_256 *out, const ecc_secret_key_256 *in1, const ecc_secret_key_256 *in2) { - /* 2^512 mod p */ + /* 2^512 mod q */ static const unsigned char C[32] = { 0x01, 0x0f, 0x9c, 0x44, 0xe3, 0x11, 0x06, 0xa4, 0x47, 0x93, 0x85, 0x68, 0xa7, 0x1b, 0x0e, 0xd0, |