openssl开源程序dh算法解析之dh_key.c

/*实现openssl 提供的默认的DH_METHOD，实现了根据密钥参数生成DH公私钥，以及根据DH 公钥(一方)以及DH 私钥(另一方)来生成一个共享密钥，用于密钥交换*/#include <stdio.h>#include "cryptlib.h"#include <openssl/bn.h>#include <openssl/rand.h>  //实现了伪随机数生成，支持用户自定义随机数生成#include <openssl/dh.h>static int generate_key(DH *dh);static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh);static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,              const BIGNUM *a, const BIGNUM *p,              const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx); //r=a^p % mstatic int dh_init(DH *dh);static int dh_finish(DH *dh);int DH_generate_key(DH *dh)      //生成公私钥{#ifdef OPENSSL_FIPS    if (FIPS_mode() && !(dh->meth->flags & DH_FLAG_FIPS_METHOD)        && !(dh->flags & DH_FLAG_NON_FIPS_ALLOW)) {        DHerr(DH_F_DH_GENERATE_KEY, DH_R_NON_FIPS_METHOD);        return 0;    }#endif    return dh->meth->generate_key(dh); //生成公私钥，存放于dh结构体的公私钥属性中}//根据对方公钥和己方DH 密钥来生成共享密钥的函数int DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh){#ifdef OPENSSL_FIPS    if (FIPS_mode() && !(dh->meth->flags & DH_FLAG_FIPS_METHOD)        && !(dh->flags & DH_FLAG_NON_FIPS_ALLOW)) {        DHerr(DH_F_DH_COMPUTE_KEY, DH_R_NON_FIPS_METHOD);        return 0;    }#endif    return dh->meth->compute_key(key, pub_key, dh);   //结果保存在key中}int DH_compute_key_padded(unsigned char *key, const BIGNUM *pub_key, DH *dh){    int rv, pad;    rv = dh->meth->compute_key(key, pub_key, dh);    if (rv <= 0)        return rv;    pad = BN_num_bytes(dh->p) - rv;  //返回dh->p的字节数    if (pad > 0) {        memmove(key + pad, key, rv);        memset(key, 0, pad);    }    return rv + pad;}static DH_METHOD dh_ossl = {    "OpenSSL DH Method",    generate_key,    compute_key,    dh_bn_mod_exp,    dh_init,    dh_finish,    0,    NULL,    NULL};const DH_METHOD *DH_OpenSSL(void){    return &dh_ossl;}static int generate_key(DH *dh)   //被DH_generate_key调用，这里具体实现{    int ok = 0;    int generate_new_key = 0;    unsigned l;    BN_CTX *ctx;  //新建上下文结构    BN_MONT_CTX *mont = NULL;    BIGNUM *pub_key = NULL, *priv_key = NULL;    ctx = BN_CTX_new();    if (ctx == NULL)        goto err;    if (dh->priv_key == NULL) {        priv_key = BN_new();  //获取私钥        if (priv_key == NULL)            goto err;        generate_new_key = 1;    } else        priv_key = dh->priv_key;    if (dh->pub_key == NULL) {        pub_key = BN_new();  //获取公钥，暂时的        if (pub_key == NULL)            goto err;    } else        pub_key = dh->pub_key;    if (dh->flags & DH_FLAG_CACHE_MONT_P) {        mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,                                      CRYPTO_LOCK_DH, dh->p, ctx);        if (!mont)            goto err;    }    if (generate_new_key) {        if (dh->q) {            do {                if (!BN_rand_range(priv_key, dh->q))//确保priv_key<dh->q                    goto err;            }            while (BN_is_zero(priv_key) || BN_is_one(priv_key));        } else {            /* secret exponent length */            l = dh->length ? dh->length : BN_num_bits(dh->p) - 1;            if (!BN_rand(priv_key, l, 0, 0))                goto err;        }    }    {        BIGNUM local_prk;        BIGNUM *prk;        if ((dh->flags & DH_FLAG_NO_EXP_CONSTTIME) == 0) {            BN_init(&local_prk);            prk = &local_prk;            BN_with_flags(prk, priv_key, BN_FLG_CONSTTIME);        } else            prk = priv_key;        //真正产生公钥        if (!dh->meth->bn_mod_exp(dh, pub_key, dh->g, prk, dh->p, ctx, mont))              goto err;    }    dh->pub_key = pub_key;   //将公私钥赋值到dh结构    dh->priv_key = priv_key;    ok = 1; err:    if (ok != 1)        DHerr(DH_F_GENERATE_KEY, ERR_R_BN_LIB);    if ((pub_key != NULL) && (dh->pub_key == NULL))        BN_free(pub_key);    if ((priv_key != NULL) && (dh->priv_key == NULL))        BN_free(priv_key);    BN_CTX_free(ctx);    return (ok);}//被DH_compute_key调用，这里具体实现static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)  {    BN_CTX *ctx = NULL;    BN_MONT_CTX *mont = NULL;    BIGNUM *tmp;    int ret = -1;    int check_result;    if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) {        DHerr(DH_F_COMPUTE_KEY, DH_R_MODULUS_TOO_LARGE);        goto err;    }    ctx = BN_CTX_new();  //新建上下文结构    if (ctx == NULL)        goto err;    BN_CTX_start(ctx);    tmp = BN_CTX_get(ctx);    if (dh->priv_key == NULL) {        DHerr(DH_F_COMPUTE_KEY, DH_R_NO_PRIVATE_VALUE);        goto err;    }    if (dh->flags & DH_FLAG_CACHE_MONT_P) {        mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,                                      CRYPTO_LOCK_DH, dh->p, ctx);        if ((dh->flags & DH_FLAG_NO_EXP_CONSTTIME) == 0) {            /* XXX */            BN_set_flags(dh->priv_key, BN_FLG_CONSTTIME);        }        if (!mont)            goto err;    }    if (!DH_check_pub_key(dh, pub_key, &check_result) || check_result) {//检查公钥合理性        DHerr(DH_F_COMPUTE_KEY, DH_R_INVALID_PUBKEY);        goto err;    }    if (!dh->        //tep=pub_key ^ dh->priv_key % dh->p，tmp就是key        meth->bn_mod_exp(dh, tmp, pub_key, dh->priv_key, dh->p, ctx, mont)) {         DHerr(DH_F_COMPUTE_KEY, ERR_R_BN_LIB);        goto err;    }    ret = BN_bn2bin(tmp, key); //转换为字节存储方式：大端法，存入key中 err:    if (ctx != NULL) {        BN_CTX_end(ctx);        BN_CTX_free(ctx);    }    return (ret);}static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,                         const BIGNUM *a, const BIGNUM *p,                         const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx){    /*     * If a is only one word long and constant time is false, use the faster     * exponenentiation function.     */    if (a->top == 1 && ((dh->flags & DH_FLAG_NO_EXP_CONSTTIME) != 0)) {        BN_ULONG A = a->d[0];        return BN_mod_exp_mont_word(r, A, p, m, ctx, m_ctx);    } else        return BN_mod_exp_mont(r, a, p, m, ctx, m_ctx);}static int dh_init(DH *dh) //初始化函数{    dh->flags |= DH_FLAG_CACHE_MONT_P;    return (1);}static int dh_finish(DH *dh)  //结束函数{    if (dh->method_mont_p)        BN_MONT_CTX_free(dh->method_mont_p);    return (1);}