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g: speed up prime generation by ~40% (1024 bit).

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We were using bn_modexp() to perform a simple modular square.
A bn_modexp_word() does this faster.

BRANCH=none
BUG=b:68167013
TEST=generate 128 primes from prng seed and verify they're same as before; tcg_test passes

Change-Id: I411a7d3fe2d68f93dc40bf74b941a637f9aa20ed
Reviewed-on: https://chromium-review.googlesource.com/778057
Commit-Ready: Marius Schilder <mschilder@chromium.org>
Tested-by: Marius Schilder <mschilder@chromium.org>
Reviewed-by: Marius Schilder <mschilder@chromium.org>
Reviewed-by: Nagendra Modadugu <ngm@google.com>
Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>
This commit is contained in:
Marius Schilder
2017-11-17 18:41:02 -08:00
committed by chrome-bot
parent c9cd870600
commit 1e855ebfcf
1 changed files with 1 additions and 4 deletions
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5
chip/g/dcrypto/bn.c
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@@ -1070,13 +1070,11 @@ static int bn_probable_prime(const struct LITE_BIGNUM *p)
int s = 0;
uint32_t ONE_buf = 1;
uint32_t TWO_buf = 2;
uint8_t r_buf[RSA_MAX_BYTES / 2];
uint8_t A_buf[RSA_MAX_BYTES / 2];
uint8_t y_buf[RSA_MAX_BYTES / 2];
struct LITE_BIGNUM ONE;
struct LITE_BIGNUM TWO;
struct LITE_BIGNUM r;
struct LITE_BIGNUM A;
struct LITE_BIGNUM y;
@@ -1105,7 +1103,6 @@ static int bn_probable_prime(const struct LITE_BIGNUM *p)
DCRYPTO_bn_wrap(&A, A_buf, bn_size(p));
DCRYPTO_bn_wrap(&y, y_buf, bn_size(p));
DCRYPTO_bn_wrap(&TWO, &TWO_buf, sizeof(TWO_buf));
for (j = 0; j < rounds; j++) {
int i;
@@ -1130,7 +1127,7 @@ static int bn_probable_prime(const struct LITE_BIGNUM *p)
/* y = y ^ 2 mod p */
for (i = 0; i < s - 1; i++) {
bn_copy(&A, &y);
bn_modexp(&y, &A, &TWO, p);
bn_modexp_word(&y, &A, 2, p);
if (bn_eq(&y, &ONE))
return 0;