diff options
| -rw-r--r-- | include/libuecc/ecc.h | 1 | ||||
| -rw-r--r-- | src/ec25519_gf.c | 51 |
2 files changed, 52 insertions, 0 deletions
diff --git a/include/libuecc/ecc.h b/include/libuecc/ecc.h index b8f8bc5..42431ec 100644 --- a/include/libuecc/ecc.h +++ b/include/libuecc/ecc.h @@ -61,6 +61,7 @@ void ecc_25519_gf_add(ecc_int_256 *out, const ecc_int_256 *in1, const ecc_int_25 void ecc_25519_gf_sub(ecc_int_256 *out, const ecc_int_256 *in1, const ecc_int_256 *in2); void ecc_25519_gf_reduce(ecc_int_256 *out, const ecc_int_256 *in); void ecc_25519_gf_mult(ecc_int_256 *out, const ecc_int_256 *in1, const ecc_int_256 *in2); +void ecc_25519_gf_recip(ecc_int_256 *out, const ecc_int_256 *in); void ecc_25519_gf_sanitize_secret(ecc_int_256 *out, const ecc_int_256 *in); diff --git a/src/ec25519_gf.c b/src/ec25519_gf.c index 6847cb1..9c57c66 100644 --- a/src/ec25519_gf.c +++ b/src/ec25519_gf.c @@ -176,6 +176,57 @@ void ecc_25519_gf_mult(ecc_int_256 *out, const ecc_int_256 *in1, const ecc_int_2 montgomery(out->p, R, C); } +void ecc_25519_gf_recip(ecc_int_256 *out, const ecc_int_256 *in) { + static const unsigned char C[32] = { + 0x01 + }; + + unsigned char A[32], B[32]; + unsigned char R1[32], R2[32]; + int use_r2 = 0; + unsigned int i, j; + + for (i = 0; i < 32; i++) { + R1[i] = (i == 0); + A[i] = in->p[i]; + } + + for (i = 0; i < 32; i++) { + unsigned char c; + + if (i == 0) + c = 0xeb; /* q[0] - 2 */ + else + c = q[i]; + + for (j = 0; j < 8; j+=2) { + if (c & (1 << j)) { + if (use_r2) + montgomery(R1, R2, A); + else + montgomery(R2, R1, A); + + use_r2 = !use_r2; + } + + montgomery(B, A, A); + + if (c & (2 << j)) { + if (use_r2) + montgomery(R1, R2, B); + else + montgomery(R2, R1, B); + + use_r2 = !use_r2; + } + + montgomery(A, B, B); + } + } + + montgomery(out->p, R2, C); +} + void ecc_25519_gf_sanitize_secret(ecc_int_256 *out, const ecc_int_256 *in) { int i; |