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Add functions for point negation and subtraction

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This commit is contained in:
Matthias Schiffer 2015-10-02 20:57:19 +09:00
parent a68abb34c2
commit 962888f03f
2 changed files with 32 additions and 0 deletions
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13
include/libuecc/ecc.h
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@ -86,6 +86,13 @@ void ecc_25519_store_packed(ecc_int256_t *out, const ecc_25519_work_t *in);
/** Checks if a point is the identity element of the Elliptic Curve group */
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
*
@ -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

19
src/ec25519.c
View file

@ -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;