openssl开源程序dh算法解析之dh_gen.c

/*----------------实现了生成 DH 密钥参数------------*///DH_generate_parameters_ex#include <stdio.h>#include "cryptlib.h"#include <openssl/bn.h>#include <openssl/dh.h>#ifdef OPENSSL_FIPS# include <openssl/fips.h>#endifstatic int dh_builtin_genparams(DH *ret, int prime_len, int generator,                                BN_GENCB *cb);int DH_generate_parameters_ex(DH *ret, int prime_len, int generator,  //产生dh参数，保存到dh结构体                              BN_GENCB *cb){#ifdef OPENSSL_FIPS  //FIPS 联邦信息处理标准是一套描述文件处理、加密算法和其他信息技术标准的标准。    if (FIPS_mode() && !(ret->meth->flags & DH_FLAG_FIPS_METHOD)        && !(ret->flags & DH_FLAG_NON_FIPS_ALLOW)) {        DHerr(DH_F_DH_GENERATE_PARAMETERS_EX, DH_R_NON_FIPS_METHOD);        return 0;    }#endif    if (ret->meth->generate_params)       //generate_params是生成DH密钥参数的回调函数        return ret->meth->generate_params(ret, prime_len, generator, cb);//产生dh参数#ifdef OPENSSL_FIPS    if (FIPS_mode())        return FIPS_dh_generate_parameters_ex(ret, prime_len, generator, cb);#endif    return dh_builtin_genparams(ret, prime_len, generator, cb);}/*- * We generate DH parameters as follows * find a prime q which is prime_len/2 bits long. * p=(2*q)+1 or (p-1)/2 = q * For this case, g is a generator if * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1. * Since the factors of p-1 are q and 2, we just need to check * g^2 mod p != 1 and g^q mod p != 1. * * Having said all that, * there is another special case method for the generators 2, 3 and 5. * for 2, p mod 24 == 11 * for 3, p mod 12 == 5  <<<<< does not work for safe primes. * for 5, p mod 10 == 3 or 7 * * Thanks to Phil Karn <[e-mail]> for the pointers about the * special generators and for answering some of my questions. * * I've implemented the second simple method :-). * Since DH should be using a safe prime (both p and q are prime), * this generator function can take a very very long time to run. *//* * Actually there is no reason to insist that 'generator' be a generator. * It's just as OK (and in some sense better) to use a generator of the * order-q subgroup. */static int dh_builtin_genparams(DH *ret, int prime_len, int generator,                                BN_GENCB *cb){    BIGNUM *t1, *t2;    int g, ok = -1;    BN_CTX *ctx = NULL;    ctx = BN_CTX_new();         //申请一个新的上下文结构    if (ctx == NULL)        goto err;    BN_CTX_start(ctx);    t1 = BN_CTX_get(ctx);  //新建一个BIGNUM结构    t2 = BN_CTX_get(ctx);    if (t1 == NULL || t2 == NULL)        goto err;    /* Make sure 'ret' has the necessary elements */    if (!ret->p && ((ret->p = BN_new()) == NULL))//新生成一个BIGNUM结构         goto err;    if (!ret->g && ((ret->g = BN_new()) == NULL))        goto err;    if (generator <= 1) {  //g>1        DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_BAD_GENERATOR);        goto err;    }    if (generator == DH_GENERATOR_2) {        //将BIGNUM结构的值置为unsigned long int类型整数的值        if (!BN_set_word(t1, 24))            goto err;        if (!BN_set_word(t2, 11))            goto err;        g = 2;    }#if 0                           /* does not work for safe primes */    else if (generator == DH_GENERATOR_3) {        if (!BN_set_word(t1, 12))            goto err;        if (!BN_set_word(t2, 5))            goto err;        g = 3;    }#endif    else if (generator == DH_GENERATOR_5) {  //g=DH_GENERATOR_5        if (!BN_set_word(t1, 10))            goto err;        if (!BN_set_word(t2, 3))            goto err;        /*         * BN_set_word(t3,7); just have to miss out on these ones          */        g = 5;    } else {        /*         * in the general case, don't worry if 'generator' is a generator or         * not: since we are using safe primes, it will generate either an         * order-q or an order-2q group, which both is OK         */        if (!BN_set_word(t1, 2))            goto err;        if (!BN_set_word(t2, 1))            goto err;        g = generator;    }    if (!BN_generate_prime_ex(ret->p, prime_len, 1, t1, t2, cb))        goto err;    if (!BN_GENCB_call(cb, 3, 0))        goto err;    if (!BN_set_word(ret->g, g))  //设置值        goto err;    ok = 1; err:    if (ok == -1) {        DHerr(DH_F_DH_BUILTIN_GENPARAMS, ERR_R_BN_LIB);        ok = 0;    }    if (ctx != NULL) {        BN_CTX_end(ctx);        BN_CTX_free(ctx);  //释放结构    }    return ok;}