[331] | 1 | /*
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| 2 | * Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
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| 3 | *
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| 4 | * Licensed under the OpenSSL license (the "License"). You may not use
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| 5 | * this file except in compliance with the License. You can obtain a copy
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| 6 | * in the file LICENSE in the source distribution or at
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| 7 | * https://www.openssl.org/source/license.html
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| 8 | */
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| 9 |
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| 10 | /*
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| 11 | * NB: These functions have been upgraded - the previous prototypes are in
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| 12 | * dh_depr.c as wrappers to these ones. - Geoff
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| 13 | */
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| 14 |
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| 15 | #include <stdio.h>
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| 16 | #include "internal/cryptlib.h"
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| 17 | #include <openssl/bn.h>
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| 18 | #include "dh_locl.h"
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| 19 |
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| 20 | static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
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| 21 | BN_GENCB *cb);
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| 22 |
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| 23 | int DH_generate_parameters_ex(DH *ret, int prime_len, int generator,
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| 24 | BN_GENCB *cb)
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| 25 | {
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| 26 | if (ret->meth->generate_params)
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| 27 | return ret->meth->generate_params(ret, prime_len, generator, cb);
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| 28 | return dh_builtin_genparams(ret, prime_len, generator, cb);
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| 29 | }
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| 30 |
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| 31 | /*-
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| 32 | * We generate DH parameters as follows
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| 33 | * find a prime q which is prime_len/2 bits long.
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| 34 | * p=(2*q)+1 or (p-1)/2 = q
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| 35 | * For this case, g is a generator if
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| 36 | * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1.
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| 37 | * Since the factors of p-1 are q and 2, we just need to check
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| 38 | * g^2 mod p != 1 and g^q mod p != 1.
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| 39 | *
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| 40 | * Having said all that,
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| 41 | * there is another special case method for the generators 2, 3 and 5.
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| 42 | * for 2, p mod 24 == 11
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| 43 | * for 3, p mod 12 == 5 <<<<< does not work for safe primes.
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| 44 | * for 5, p mod 10 == 3 or 7
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| 45 | *
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| 46 | * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the
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| 47 | * special generators and for answering some of my questions.
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| 48 | *
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| 49 | * I've implemented the second simple method :-).
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| 50 | * Since DH should be using a safe prime (both p and q are prime),
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| 51 | * this generator function can take a very very long time to run.
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| 52 | */
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| 53 | /*
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| 54 | * Actually there is no reason to insist that 'generator' be a generator.
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| 55 | * It's just as OK (and in some sense better) to use a generator of the
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| 56 | * order-q subgroup.
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| 57 | */
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| 58 | static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
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| 59 | BN_GENCB *cb)
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| 60 | {
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| 61 | BIGNUM *t1, *t2;
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| 62 | int g, ok = -1;
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| 63 | BN_CTX *ctx = NULL;
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| 64 |
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| 65 | ctx = BN_CTX_new();
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| 66 | if (ctx == NULL)
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| 67 | goto err;
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| 68 | BN_CTX_start(ctx);
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| 69 | t1 = BN_CTX_get(ctx);
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| 70 | t2 = BN_CTX_get(ctx);
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| 71 | if (t1 == NULL || t2 == NULL)
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| 72 | goto err;
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| 73 |
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| 74 | /* Make sure 'ret' has the necessary elements */
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| 75 | if (!ret->p && ((ret->p = BN_new()) == NULL))
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| 76 | goto err;
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| 77 | if (!ret->g && ((ret->g = BN_new()) == NULL))
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| 78 | goto err;
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| 79 |
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| 80 | if (generator <= 1) {
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| 81 | DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_BAD_GENERATOR);
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| 82 | goto err;
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| 83 | }
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| 84 | if (generator == DH_GENERATOR_2) {
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| 85 | if (!BN_set_word(t1, 24))
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| 86 | goto err;
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| 87 | if (!BN_set_word(t2, 11))
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| 88 | goto err;
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| 89 | g = 2;
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| 90 | } else if (generator == DH_GENERATOR_5) {
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| 91 | if (!BN_set_word(t1, 10))
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| 92 | goto err;
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| 93 | if (!BN_set_word(t2, 3))
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| 94 | goto err;
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| 95 | /*
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| 96 | * BN_set_word(t3,7); just have to miss out on these ones :-(
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| 97 | */
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| 98 | g = 5;
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| 99 | } else {
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| 100 | /*
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| 101 | * in the general case, don't worry if 'generator' is a generator or
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| 102 | * not: since we are using safe primes, it will generate either an
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| 103 | * order-q or an order-2q group, which both is OK
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| 104 | */
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| 105 | if (!BN_set_word(t1, 2))
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| 106 | goto err;
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| 107 | if (!BN_set_word(t2, 1))
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| 108 | goto err;
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| 109 | g = generator;
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| 110 | }
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| 111 |
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| 112 | if (!BN_generate_prime_ex(ret->p, prime_len, 1, t1, t2, cb))
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| 113 | goto err;
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| 114 | if (!BN_GENCB_call(cb, 3, 0))
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| 115 | goto err;
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| 116 | if (!BN_set_word(ret->g, g))
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| 117 | goto err;
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| 118 | ok = 1;
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| 119 | err:
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| 120 | if (ok == -1) {
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| 121 | DHerr(DH_F_DH_BUILTIN_GENPARAMS, ERR_R_BN_LIB);
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| 122 | ok = 0;
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| 123 | }
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| 124 |
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| 125 | if (ctx != NULL) {
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| 126 | BN_CTX_end(ctx);
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| 127 | BN_CTX_free(ctx);
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| 128 | }
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| 129 | return ok;
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| 130 | }
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