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-rw-r--r--src/ec25519.c29
1 files changed, 16 insertions, 13 deletions
diff --git a/src/ec25519.c b/src/ec25519.c
index 6458d2d..d35e368 100644
--- a/src/ec25519.c
+++ b/src/ec25519.c
@@ -194,15 +194,16 @@ static const unsigned int rho_s[32] = {
};
static const unsigned int zero[32] = {0};
-static const unsigned int minus1[32] = {
- 0xec, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
- 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
- 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
- 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x7f
-};
static void square_root(unsigned int out[32], const unsigned int z[32]) {
- /* raise z to the (2^252-2)th power */
+ static const unsigned int minus1[32] = {
+ 0xec, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x7f
+ };
+
+ /* raise z to power (2^252-2), check if power (2^253-5) equals -1 */
unsigned int z2[32];
unsigned int z9[32];
@@ -214,7 +215,8 @@ static void square_root(unsigned int out[32], const unsigned int z[32]) {
unsigned int z2_100_0[32];
unsigned int t0[32];
unsigned int t1[32];
- unsigned int rt_sq[32];
+ unsigned int z2_252_1[32];
+ unsigned int z2_252_1_rho_s[32];
int i;
/* 2 */ square(z2, z);
@@ -264,14 +266,15 @@ static void square_root(unsigned int out[32], const unsigned int z[32]) {
/* 2^251 - 2^1 */ square(t1, t0);
/* 2^252 - 2^2 */ square(t0, t1);
+ /* 2^252 - 2^1 */ mult(z2_252_1, t0, z2);
- /* 2^252 - 2 */ mult(t1, t0, z2);
-
- mult(t0, t1, rho_s);
+ /* 2^253 - 2^3 */ square(t1, t0);
+ /* 2^253 - 6 */ mult(t0, t1, z2);
+ /* 2^253 - 5 */ mult(t1, t0, z);
- square(rt_sq, t1);
+ mult(z2_252_1_rho_s, z2_252_1, rho_s);
- select(out, t0, t1, check_equal(rt_sq, minus1));
+ select(out, z2_252_1_rho_s, z2_252_1, check_equal(t1, minus1));
}
static void recip(unsigned int out[32], const unsigned int z[32]) {