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-rw-r--r--src/ec25519_gf.c51
1 files changed, 51 insertions, 0 deletions
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;