1 /* 2 * Copyright 1995-2017 The OpenSSL Project Authors. All Rights Reserved. 3 * 4 * Licensed under the OpenSSL license (the "License"). You may not use 5 * this file except in compliance with the License. You can obtain a copy 6 * in the file LICENSE in the source distribution or at 7 * https://www.openssl.org/source/license.html 8 */ 9 10 /* 11 * NB: These functions have been upgraded - the previous prototypes are in 12 * dh_depr.c as wrappers to these ones. - Geoff 13 */ 14 15 #include <stdio.h> 16 #include "internal/cryptlib.h" 17 #include <openssl/bn.h> 18 #include "dh_locl.h" 19 20 static int dh_builtin_genparams(DH *ret, int prime_len, int generator, 21 BN_GENCB *cb); 22 23 int DH_generate_parameters_ex(DH *ret, int prime_len, int generator, 24 BN_GENCB *cb) 25 { 26 if (ret->meth->generate_params) 27 return ret->meth->generate_params(ret, prime_len, generator, cb); 28 return dh_builtin_genparams(ret, prime_len, generator, cb); 29 } 30 31 /*- 32 * We generate DH parameters as follows 33 * find a prime q which is prime_len/2 bits long. 34 * p=(2*q)+1 or (p-1)/2 = q 35 * For this case, g is a generator if 36 * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1. 37 * Since the factors of p-1 are q and 2, we just need to check 38 * g^2 mod p != 1 and g^q mod p != 1. 39 * 40 * Having said all that, 41 * there is another special case method for the generators 2, 3 and 5. 42 * for 2, p mod 24 == 11 43 * for 3, p mod 12 == 5 <<<<< does not work for safe primes. 44 * for 5, p mod 10 == 3 or 7 45 * 46 * Thanks to Phil Karn for the pointers about the 47 * special generators and for answering some of my questions. 48 * 49 * I've implemented the second simple method :-). 50 * Since DH should be using a safe prime (both p and q are prime), 51 * this generator function can take a very very long time to run. 52 */ 53 /* 54 * Actually there is no reason to insist that 'generator' be a generator. 55 * It's just as OK (and in some sense better) to use a generator of the 56 * order-q subgroup. 57 */ 58 static int dh_builtin_genparams(DH *ret, int prime_len, int generator, 59 BN_GENCB *cb) 60 { 61 BIGNUM *t1, *t2; 62 int g, ok = -1; 63 BN_CTX *ctx = NULL; 64 65 ctx = BN_CTX_new(); 66 if (ctx == NULL) 67 goto err; 68 BN_CTX_start(ctx); 69 t1 = BN_CTX_get(ctx); 70 t2 = BN_CTX_get(ctx); 71 if (t2 == NULL) 72 goto err; 73 74 /* Make sure 'ret' has the necessary elements */ 75 if (!ret->p && ((ret->p = BN_new()) == NULL)) 76 goto err; 77 if (!ret->g && ((ret->g = BN_new()) == NULL)) 78 goto err; 79 80 if (generator <= 1) { 81 DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_BAD_GENERATOR); 82 goto err; 83 } 84 if (generator == DH_GENERATOR_2) { 85 if (!BN_set_word(t1, 24)) 86 goto err; 87 if (!BN_set_word(t2, 11)) 88 goto err; 89 g = 2; 90 } else if (generator == DH_GENERATOR_5) { 91 if (!BN_set_word(t1, 10)) 92 goto err; 93 if (!BN_set_word(t2, 3)) 94 goto err; 95 /* 96 * BN_set_word(t3,7); just have to miss out on these ones :-( 97 */ 98 g = 5; 99 } else { 100 /* 101 * in the general case, don't worry if 'generator' is a generator or 102 * not: since we are using safe primes, it will generate either an 103 * order-q or an order-2q group, which both is OK 104 */ 105 if (!BN_set_word(t1, 2)) 106 goto err; 107 if (!BN_set_word(t2, 1)) 108 goto err; 109 g = generator; 110 } 111 112 if (!BN_generate_prime_ex(ret->p, prime_len, 1, t1, t2, cb)) 113 goto err; 114 if (!BN_GENCB_call(cb, 3, 0)) 115 goto err; 116 if (!BN_set_word(ret->g, g)) 117 goto err; 118 ok = 1; 119 err: 120 if (ok == -1) { 121 DHerr(DH_F_DH_BUILTIN_GENPARAMS, ERR_R_BN_LIB); 122 ok = 0; 123 } 124 125 if (ctx != NULL) { 126 BN_CTX_end(ctx); 127 BN_CTX_free(ctx); 128 } 129 return ok; 130 } 131