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66 lines
2.0 KiB
Diff
66 lines
2.0 KiB
Diff
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From 2232d3d5f188b65dbb6c823ac62175412739eb16 Mon Sep 17 00:00:00 2001
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From: Jouni Malinen <j@w1.fi>
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Date: Fri, 7 Jan 2022 13:47:16 +0200
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Subject: [PATCH 2/4] dragonfly: Add sqrt() helper function
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This is a backport of "SAE: Move sqrt() implementation into a helper
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function" to introduce the helper function needed for the following
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patches.
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Signed-off-by: Jouni Malinen <j@w1.fi>
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---
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src/common/dragonfly.c | 34 ++++++++++++++++++++++++++++++++++
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src/common/dragonfly.h | 2 ++
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2 files changed, 36 insertions(+)
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--- a/src/common/dragonfly.c
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+++ b/src/common/dragonfly.c
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@@ -213,3 +213,37 @@ int dragonfly_generate_scalar(const stru
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"dragonfly: Unable to get randomness for own scalar");
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return -1;
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}
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+
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+
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+/* res = sqrt(val) */
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+int dragonfly_sqrt(struct crypto_ec *ec, const struct crypto_bignum *val,
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+ struct crypto_bignum *res)
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+{
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+ const struct crypto_bignum *prime;
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+ struct crypto_bignum *tmp, *one;
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+ int ret = 0;
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+ u8 prime_bin[DRAGONFLY_MAX_ECC_PRIME_LEN];
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+ size_t prime_len;
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+
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+ /* For prime p such that p = 3 mod 4, sqrt(w) = w^((p+1)/4) mod p */
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+
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+ prime = crypto_ec_get_prime(ec);
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+ prime_len = crypto_ec_prime_len(ec);
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+ tmp = crypto_bignum_init();
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+ one = crypto_bignum_init_uint(1);
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+
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+ if (crypto_bignum_to_bin(prime, prime_bin, sizeof(prime_bin),
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+ prime_len) < 0 ||
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+ (prime_bin[prime_len - 1] & 0x03) != 3 ||
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+ !tmp || !one ||
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+ /* tmp = (p+1)/4 */
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+ crypto_bignum_add(prime, one, tmp) < 0 ||
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+ crypto_bignum_rshift(tmp, 2, tmp) < 0 ||
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+ /* res = sqrt(val) */
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+ crypto_bignum_exptmod(val, tmp, prime, res) < 0)
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+ ret = -1;
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+
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+ crypto_bignum_deinit(tmp, 0);
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+ crypto_bignum_deinit(one, 0);
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+ return ret;
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+}
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--- a/src/common/dragonfly.h
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+++ b/src/common/dragonfly.h
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@@ -27,5 +27,7 @@ int dragonfly_generate_scalar(const stru
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struct crypto_bignum *_rand,
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struct crypto_bignum *_mask,
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struct crypto_bignum *scalar);
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+int dragonfly_sqrt(struct crypto_ec *ec, const struct crypto_bignum *val,
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+ struct crypto_bignum *res);
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#endif /* DRAGONFLY_H */
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