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Unify Curve25519 scalar masking functions.

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The C functions `x25519_scalar_mask()` and `GFp_ed25519_scalar_mask()` are
equivalent. Just keep one, with an updated name. We prefer the implementation
that most closely tracks the X25519 and Ed25519 RFCs.

I agree to license my contributions to each file under the terms given
at the top of each file I changed.
This commit is contained in:
Joe Ranweiler 2017-05-03 15:12:42 -07:00
parent ee84bc9b80
commit 503116373d
2 changed files with 7 additions and 16 deletions
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19
crypto/curve25519/curve25519.c
View File

@ -30,6 +30,7 @@
/* Prevent -Wmissing-prototypes warnings. */
void GFp_curve25519_scalar_mask(uint8_t a[32]);
void GFp_fe_invert(fe out, const fe z);
uint8_t GFp_fe_isnegative(const fe f);
void GFp_fe_mul(fe h, const fe f, const fe g);
@ -4520,13 +4521,9 @@ void GFp_x25519_sc_muladd(uint8_t *s, const uint8_t *a, const uint8_t *b,
s[31] = (uint8_t)(s11 >> 17);
}
/* Prototype to avoid -Wmissing-prototypes warnings. */
void GFp_ed25519_scalar_mask(uint8_t a[32]);
void GFp_ed25519_scalar_mask(uint8_t a[32]) {
void GFp_curve25519_scalar_mask(uint8_t a[32]) {
a[0] &= 248;
a[31] &= 63;
a[31] &= 127;
a[31] |= 64;
}
@ -4618,12 +4615,6 @@ static void GFp_fe_mul121666(fe h, fe f) {
h[9] = (int32_t)h9;
}
static void x25519_scalar_mask(uint8_t e[32]) {
e[0] &= 248;
e[31] &= 127;
e[31] |= 64;
}
static void x25519_scalar_mult_generic(uint8_t out[32],
const uint8_t scalar[32],
const uint8_t point[32]) {
@ -4631,7 +4622,7 @@ static void x25519_scalar_mult_generic(uint8_t out[32],
uint8_t e[32];
memcpy(e, scalar, 32);
x25519_scalar_mask(e);
GFp_curve25519_scalar_mask(e);
fe_frombytes(x1, point);
fe_1(x2);
fe_0(z2);
@ -4718,7 +4709,7 @@ void GFp_x25519_public_from_private(uint8_t out_public_value[32],
uint8_t e[32];
memcpy(e, private_key, 32);
x25519_scalar_mask(e);
GFp_curve25519_scalar_mask(e);
ge_p3 A;
GFp_x25519_ge_scalarmult_base(&A, e);

4
src/ec/curve25519/ed25519.rs
View File

@ -150,7 +150,7 @@ impl<'a> Ed25519KeyPair {
let mut scalar = [0u8; SCALAR_LEN];
scalar.copy_from_slice(&scalar_encoded);
unsafe { GFp_ed25519_scalar_mask(&mut scalar) };
unsafe { GFp_curve25519_scalar_mask(&mut scalar) };
let mut prefix = [0u8; PREFIX_LEN];
prefix.copy_from_slice(prefix_encoded);
@ -289,7 +289,7 @@ fn digest_scalar(digest: digest::Digest) -> Scalar {
}
extern {
fn GFp_ed25519_scalar_mask(a: &mut Scalar);
fn GFp_curve25519_scalar_mask(a: &mut Scalar);
fn GFp_ge_double_scalarmult_vartime(r: &mut Point, a_coeff: &Scalar,
a: &ExtPoint, b_coeff: &Scalar);
fn GFp_x25519_ge_scalarmult_base(h: &mut ExtPoint, a: &Seed);