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-rw-r--r--src/ec25519_secret.c63
1 files changed, 21 insertions, 42 deletions
diff --git a/src/ec25519_secret.c b/src/ec25519_secret.c
index fd703d6..5819a6c 100644
--- a/src/ec25519_secret.c
+++ b/src/ec25519_secret.c
@@ -34,6 +34,7 @@
#define IS_NEGATIVE(n) ((int)((((unsigned)n) >> (8*sizeof(n)-1))&1))
+#define ASR(n,s) (((n) >> s)|(IS_NEGATIVE(n)*((unsigned)-1) << (8*sizeof(n)-s)))
static const unsigned char q[32] = {
@@ -71,58 +72,36 @@ int ecc_25519_secret_is_zero(const ecc_secret_key_256 *in) {
void ecc_25519_secret_add(ecc_secret_key_256 *out, const ecc_secret_key_256 *in1, const ecc_secret_key_256 *in2) {
unsigned int j;
- int u1, u2, u3;
- unsigned char out1[32], out2[32], out3[32];
+ unsigned int u;
+ int nq = 1 - (in1->s[31]>>4) - (in2->s[31]>>4);
- u1 = u2 = u3 = 0;
- for (j = 0; j < 31; ++j) {
- u1 += in1->s[j] + in2->s[j];
- u2 += in1->s[j] + in2->s[j] - 8*q[j];
- u3 += in1->s[j] + in2->s[j] - 16*q[j];
-
- out1[j] = u1; out2[j] = u2; out3[j] = u3;
- u1 = (u1+IS_NEGATIVE(u1))/256 - IS_NEGATIVE(u1);
- u2 = (u2+IS_NEGATIVE(u2))/256 - IS_NEGATIVE(u2);
- u3 = (u3+IS_NEGATIVE(u3))/256 - IS_NEGATIVE(u3);
- }
- u1 += in1->s[31] + in2->s[31];
- u2 += in1->s[31] + in2->s[31] - 8*q[31];
- u3 += in1->s[31] + in2->s[31] - 16*q[31];
- out1[31] = u1; out2[31] = u2; out3[31] = u3;
+ u = 0;
+ for (j = 0; j < 32; ++j) {
+ u += in1->s[j] + in2->s[j] + nq*q[j];
- select(out->s, out1, out2, (u1 >> 8) & 1);
- select(out->s, out->s, out3, ((u1 >> 8) & (u2 >> 8)) & 1);
+ out->s[j] = u;
+ u = ASR(u, 8);
+ }
}
void ecc_25519_secret_sub(ecc_secret_key_256 *out, const ecc_secret_key_256 *in1, const ecc_secret_key_256 *in2) {
unsigned int j;
- int u1, u2, u3;
- unsigned char out1[32], out2[32], out3[32];
+ unsigned int u;
+ int nq = 8 - (in1->s[31]>>4) + (in2->s[31]>>4);
- u1 = u2 = u3 = 0;
- for (j = 0; j < 31; ++j) {
- u1 += in1->s[j] - in2->s[j] + 16*q[j];
- u2 += in1->s[j] - in2->s[j] + 8*q[j];
- u3 += in1->s[j] - in2->s[j];
-
- out1[j] = u1; out2[j] = u2; out3[j] = u3;
- u1 = (u1+IS_NEGATIVE(u1))/256 - IS_NEGATIVE(u1);
- u2 = (u2+IS_NEGATIVE(u2))/256 - IS_NEGATIVE(u2);
- u3 = (u3+IS_NEGATIVE(u3))/256 - IS_NEGATIVE(u3);
- }
- u1 += in1->s[31] - in2->s[31] + 16*q[31];
- u2 += in1->s[31] - in2->s[31] + 8*q[31];
- u3 += in1->s[31] - in2->s[31];
- out1[31] = u1; out2[31] = u2; out3[31] = u3;
+ u = 0;
+ for (j = 0; j < 32; ++j) {
+ u += in1->s[j] - in2->s[j] + nq*q[j];
- select(out->s, out1, out2, (u1 >> 8) & 1);
- select(out->s, out->s, out3, ((u1 >> 8) & (u2 >> 8)) & 1);
+ out->s[j] = u;
+ u = ASR(u, 8);
+ }
}
static void reduce(unsigned char a[32]) {
unsigned int j;
- int nq = a[31] >> 4;
- int u1, u2;
+ unsigned int nq = a[31] >> 4;
+ unsigned int u1, u2;
unsigned char out1[32], out2[32];
u1 = u2 = 0;
@@ -131,8 +110,8 @@ static void reduce(unsigned char a[32]) {
u2 += a[j] - (nq-1)*q[j];
out1[j] = u1; out2[j] = u2;
- u1 = (u1+IS_NEGATIVE(u1))/256 - IS_NEGATIVE(u1);
- u2 = (u2+IS_NEGATIVE(u2))/256 - IS_NEGATIVE(u2);
+ u1 = ASR(u1, 8);
+ u2 = ASR(u2, 8);
}
u1 += a[31] - nq*q[31];
u2 += a[31] - (nq-1)*q[31];