diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/ec25519.c | 46 |
1 files changed, 36 insertions, 10 deletions
diff --git a/src/ec25519.c b/src/ec25519.c index f77fcff..d21bb8a 100644 --- a/src/ec25519.c +++ b/src/ec25519.c @@ -40,6 +40,10 @@ #include <libuecc/ecc.h> +static const unsigned int zero[32] = {0}; +static const unsigned int one[32] = {1}; + + /** Adds two unpacked integers (modulo p) */ static void add(unsigned int out[32], const unsigned int a[32], const unsigned int b[32]) { unsigned int j; @@ -114,7 +118,7 @@ static void mult(unsigned int out[32], const unsigned int a[32], const unsigned } /** Multiplies an unpacked integer with a small integer (modulo p) */ -static void mult_int(unsigned int out[32], const unsigned int n, const unsigned int a[32]) { +static void mult_int(unsigned int out[32], unsigned int n, const unsigned int a[32]) { unsigned int j; unsigned int u; @@ -165,7 +169,6 @@ static int check_equal(const unsigned int x[32], const unsigned int y[32]) { * The intergers must be must be \ref squeeze "squeezed" before. */ static int check_zero(const unsigned int x[32]) { - static const unsigned int zero[32] = {0}; static const unsigned int p[32] = { 0xed, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, @@ -214,9 +217,9 @@ static void select(unsigned int out[32], const unsigned int r[32], const unsigne /** * Computes the square root of an unpacked integer (in the prime field modulo p) * - * If the given integer has no square root, the result is undefined. + * If the given integer has no square root, 0 is returned, 1 otherwise. */ -static void square_root(unsigned int out[32], const unsigned int z[32]) { +static int square_root(unsigned int out[32], const unsigned int z[32]) { static const unsigned int minus1[32] = { 0xec, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, @@ -303,6 +306,10 @@ static void square_root(unsigned int out[32], const unsigned int z[32]) { mult(z2_252_1_rho_s, z2_252_1, rho_s); select(out, z2_252_1, z2_252_1_rho_s, check_equal(t1, minus1)); + + /* Check the root */ + square(t0, out); + return check_equal(t0, z); } /** Computes the reciprocal of an unpacked integer (in the prime field modulo p) */ @@ -373,8 +380,9 @@ static void recip(unsigned int out[32], const unsigned int z[32]) { } /** Loads a point with given coordinates into its unpacked representation */ -void ecc_25519_load_xy(ecc_25519_work_t *out, const ecc_int256_t *x, const ecc_int256_t *y) { +int ecc_25519_load_xy(ecc_25519_work_t *out, const ecc_int256_t *x, const ecc_int256_t *y) { int i; + unsigned int X2[32], Y2[32], aX2[32], dX2[32], dX2Y2[32], aX2_Y2[32], _1_dX2Y2[32], r[32]; for (i = 0; i < 32; i++) { out->X[i] = x->p[i]; @@ -382,7 +390,23 @@ void ecc_25519_load_xy(ecc_25519_work_t *out, const ecc_int256_t *x, const ecc_i out->Z[i] = (i == 0); } + /* Check validity */ + square(X2, out->X); + square(Y2, out->Y); + mult_int(aX2, 486664, X2); + mult_int(dX2, 486660, X2); + mult(dX2Y2, dX2, Y2); + add(aX2_Y2, aX2, Y2); + add(_1_dX2Y2, one, dX2Y2); + sub(r, aX2_Y2, _1_dX2Y2); + squeeze(r); + + if (!check_zero(r)) + return 0; + mult(out->T, out->X, out->Y); + + return 1; } /** @@ -414,10 +438,7 @@ void ecc_25519_store_xy(ecc_int256_t *x, ecc_int256_t *y, const ecc_25519_work_t } /** Loads a packed point into its unpacked representation */ -void ecc_25519_load_packed(ecc_25519_work_t *out, const ecc_int256_t *in) { - static const unsigned int zero[32] = {0}; - static const unsigned int one[32] = {1}; - +int ecc_25519_load_packed(ecc_25519_work_t *out, const ecc_int256_t *in) { int i; unsigned int X2[32] /* X^2 */, aX2[32] /* aX^2 */, dX2[32] /* dX^2 */, _1_aX2[32] /* 1-aX^2 */, _1_dX2[32] /* 1-aX^2 */; unsigned int _1_1_dX2[32] /* 1/(1-aX^2) */, Y2[32] /* Y^2 */, Y[32], Yt[32]; @@ -436,12 +457,17 @@ void ecc_25519_load_packed(ecc_25519_work_t *out, const ecc_int256_t *in) { sub(_1_dX2, one, dX2); recip(_1_1_dX2, _1_dX2); mult(Y2, _1_aX2, _1_1_dX2); - square_root(Y, Y2); + + if (!square_root(Y, Y2)) + return 0; + sub(Yt, zero, Y); select(out->Y, Y, Yt, (in->p[31] >> 7) ^ (Y[0] & 1)); mult(out->T, out->X, out->Y); + + return 1; } /** Stores a point into its packed representation */ |