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tls: code shrink in curve 25519

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function                                             old     new   delta
curve25519                                           832     849     +17
curve_x25519_compute_pubkey_and_premaster             74      71      -3
static.basepoint9                                     32       -     -32
------------------------------------------------------------------------------
(add/remove: 0/1 grow/shrink: 1/1 up/down: 17/-35)            Total: -18 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2021-04-28 12:19:24 +02:00
parent acd3079fd1
commit b35eef5383
1 changed files with 26 additions and 18 deletions
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44
networking/tls_fe.c
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@ -108,26 +108,26 @@ static void raw_try_sub(byte *x, const byte *p)
#if 0 //UNUSED
static int prime_msb(const byte *p)
{
int i;
byte x;
int shift = 1;
int z = F25519_SIZE - 1;
int i;
byte x;
int shift = 1;
int z = F25519_SIZE - 1;
/*
Test for any hot bits.
As soon as one instance is encountered set shift to 0.
*/
/*
Test for any hot bits.
As soon as one instance is encountered set shift to 0.
*/
for (i = F25519_SIZE - 1; i >= 0; i--) {
shift &= ((shift ^ ((-p[i] | p[i]) >> 7)) & 1);
z -= shift;
}
shift &= ((shift ^ ((-p[i] | p[i]) >> 7)) & 1);
z -= shift;
}
x = p[z];
z <<= 3;
shift = 1;
for (i = 0; i < 8; i++) {
shift &= ((-(x >> i) | (x >> i)) >> (7 - i) & 1);
z += shift;
}
shift = 1;
for (i = 0; i < 8; i++) {
shift &= ((-(x >> i) | (x >> i)) >> (7 - i) & 1);
z += shift;
}
return z - 1;
}
@ -549,6 +549,9 @@ static void curve25519(byte *result, const byte *e, const byte *q)
int i;
struct {
/* for bbox's special case of q == NULL meaning "use basepoint" */
/*static const*/ uint8_t basepoint9[CURVE25519_KEYSIZE]; // = {9};
/* from wolfssl-3.15.3/wolfssl/wolfcrypt/fe_operations.h */
/*static const*/ byte f25519_one[F25519_SIZE]; // = {1};
@ -559,6 +562,7 @@ static void curve25519(byte *result, const byte *e, const byte *q)
byte xm1[F25519_SIZE]; // = {1};
byte zm1[F25519_SIZE]; // = {0};
} z;
#define basepoint9 z.basepoint9
#define f25519_one z.f25519_one
#define xm z.xm
#define zm z.zm
@ -569,6 +573,11 @@ static void curve25519(byte *result, const byte *e, const byte *q)
zm[0] = 1;
xm1[0] = 1;
if (!q) {
basepoint9[0] = 9;
q = basepoint9;
}
/* Note: bit 254 is assumed to be 1 */
lm_copy(xm, q);
@ -606,7 +615,6 @@ void FAST_FUNC curve_x25519_compute_pubkey_and_premaster(
uint8_t *pubkey, uint8_t *premaster,
const uint8_t *peerkey32)
{
static const uint8_t basepoint9[CURVE25519_KEYSIZE] ALIGN8 = {9};
uint8_t privkey[CURVE25519_KEYSIZE]; //[32]
/* Generate random private key, see RFC 7748 */
@ -615,7 +623,7 @@ void FAST_FUNC curve_x25519_compute_pubkey_and_premaster(
privkey[CURVE25519_KEYSIZE-1] = ((privkey[CURVE25519_KEYSIZE-1] & 0x7f) | 0x40);
/* Compute public key */
curve25519(pubkey, privkey, basepoint9);
curve25519(pubkey, privkey, NULL /* "use base point of x25519" */);
/* Compute premaster using peer's public key */
curve25519(premaster, privkey, peerkey32);