diff options
| -rw-r--r-- | include/libuecc/ecc.h | 13 | ||||
| -rw-r--r-- | src/ec25519.c | 19 |
2 files changed, 32 insertions, 0 deletions
diff --git a/include/libuecc/ecc.h b/include/libuecc/ecc.h index 982f7c9..5d75150 100644 --- a/include/libuecc/ecc.h +++ b/include/libuecc/ecc.h @@ -87,6 +87,13 @@ void ecc_25519_store_packed(ecc_int256_t *out, const ecc_25519_work_t *in); int ecc_25519_is_identity(const ecc_25519_work_t *in); /** + * Negates a point of the Elliptic Curve + * + * The same pointer may be given for input and output + */ +void ecc_25519_negate(ecc_25519_work_t *out, const ecc_25519_work_t *in); + +/** * Doubles a point of the Elliptic Curve * * ecc_25519_double(out, in) is equivalent to ecc_25519_add(out, in, in), but faster. @@ -102,6 +109,12 @@ void ecc_25519_double(ecc_25519_work_t *out, const ecc_25519_work_t *in); */ void ecc_25519_add(ecc_25519_work_t *out, const ecc_25519_work_t *in1, const ecc_25519_work_t *in2); +/** + * Subtracts two points of the Elliptic Curve + * + * The same pointers may be given for input and output. + */ +void ecc_25519_sub(ecc_25519_work_t *out, const ecc_25519_work_t *in1, const ecc_25519_work_t *in2); /** * Does a scalar multiplication of a point of the Elliptic Curve with an integer of a given bit length diff --git a/src/ec25519.c b/src/ec25519.c index a9d519c..d673aee 100644 --- a/src/ec25519.c +++ b/src/ec25519.c @@ -498,6 +498,18 @@ int ecc_25519_is_identity(const ecc_25519_work_t *in) { return (check_zero(in->X)&check_zero(Y_Z)); } +void ecc_25519_negate(ecc_25519_work_t *out, const ecc_25519_work_t *in) { + int i; + + for (i = 0; i < 32; i++) { + out->Y[i] = in->Y[i]; + out->Z[i] = in->Z[i]; + } + + sub(out->X, zero, in->X); + sub(out->T, zero, in->T); +} + void ecc_25519_double(ecc_25519_work_t *out, const ecc_25519_work_t *in) { unsigned int A[32], B[32], C[32], D[32], E[32], F[32], G[32], H[32], t0[32], t1[32], t2[32], t3[32]; @@ -542,6 +554,13 @@ void ecc_25519_add(ecc_25519_work_t *out, const ecc_25519_work_t *in1, const ecc mult(out->Z, F, G); } +void ecc_25519_sub(ecc_25519_work_t *out, const ecc_25519_work_t *in1, const ecc_25519_work_t *in2) { + ecc_25519_work_t in2_neg; + + ecc_25519_negate(&in2_neg, in2); + ecc_25519_add(out, in1, &in2_neg); +} + void ecc_25519_scalarmult_bits(ecc_25519_work_t *out, const ecc_int256_t *n, const ecc_25519_work_t *base, unsigned bits) { ecc_25519_work_t Q2, Q2p; ecc_25519_work_t cur = ecc_25519_work_identity; |