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ddb13b283b
Longer private key sizes unnecessarily raise the cycles needed to compute the shared secret without any increase of the real security. We use minimum key sizes as defined in RFC7919. For arbitrary parameters we cannot know whether they are safe primes (we could test but that would be too inefficient) we have to keep generating large keys. However we now set a small dh->length when we are generating safe prime parameters because we know it is safe to use small keys with them. That means users need to regenerate the parameters if they want to take the performance advantage of small private key. Reviewed-by: Kurt Roeckx <kurt@roeckx.be> Reviewed-by: Paul Dale <pauli@openssl.org> Reviewed-by: Hugo Landau <hlandau@openssl.org> (Merged from https://github.com/openssl/openssl/pull/18480)
61 lines
1.8 KiB
C
61 lines
1.8 KiB
C
/*
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* Copyright 2019-2021 The OpenSSL Project Authors. All Rights Reserved.
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*
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* Licensed under the Apache License 2.0 (the "License"). You may not use
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* this file except in compliance with the License. You can obtain a copy
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* in the file LICENSE in the source distribution or at
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* https://www.openssl.org/source/license.html
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*/
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#include "internal/ffc.h"
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/*
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* SP800-56Ar3 5.6.1.1.4 Key pair generation by testing candidates.
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* Generates a private key in the interval [1, min(2 ^ N - 1, q - 1)].
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*
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* ctx must be set up with a libctx (for fips mode).
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* params contains the FFC domain parameters p, q and g (for DH or DSA).
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* N is the maximum bit length of the generated private key,
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* s is the security strength.
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* priv_key is the returned private key,
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*/
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int ossl_ffc_generate_private_key(BN_CTX *ctx, const FFC_PARAMS *params,
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int N, int s, BIGNUM *priv)
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{
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int ret = 0, qbits = BN_num_bits(params->q);
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BIGNUM *m, *two_powN = NULL;
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/* Deal with the edge cases where the value of N and/or s is not set */
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if (s == 0)
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goto err;
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if (N == 0)
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N = params->keylength ? params->keylength : 2 * s;
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/* Step (2) : check range of N */
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if (N < 2 * s || N > qbits)
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return 0;
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two_powN = BN_new();
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/* 2^N */
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if (two_powN == NULL || !BN_lshift(two_powN, BN_value_one(), N))
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goto err;
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/* Step (5) : M = min(2 ^ N, q) */
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m = (BN_cmp(two_powN, params->q) > 0) ? params->q : two_powN;
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do {
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/* Steps (3, 4 & 7) : c + 1 = 1 + random[0..2^N - 1] */
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if (!BN_priv_rand_range_ex(priv, two_powN, 0, ctx)
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|| !BN_add_word(priv, 1))
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goto err;
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/* Step (6) : loop if c > M - 2 (i.e. c + 1 >= M) */
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if (BN_cmp(priv, m) < 0)
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break;
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} while (1);
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ret = 1;
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err:
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BN_free(two_powN);
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return ret;
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}
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