Question

我正在尝试生成Hmac-sha1的一小段代码。我被要求使用OpenSSL库来自行编码hmac实现以进行SHA1计算。在'wiki'ing算法之后，这是我在下面的内容。我使用了RFC 2246指定测试值的输入：

   Count    Hexadecimal HMAC-SHA-1(secret, count)
   0        cc93cf18508d94934c64b65d8ba7667fb7cde4b0
   1        75a48a19d4cbe100644e8ac1397eea747a2d33ab
   2        0bacb7fa082fef30782211938bc1c5e70416ff44
   3        66c28227d03a2d5529262ff016a1e6ef76557ece
   4        a904c900a64b35909874b33e61c5938a8e15ed1c
   5        a37e783d7b7233c083d4f62926c7a25f238d0316
   6        bc9cd28561042c83f219324d3c607256c03272ae
   7        a4fb960c0bc06e1eabb804e5b397cdc4b45596fa
   8        1b3c89f65e6c9e883012052823443f048b4332db
   9        1637409809a679dc698207310c8c7fc07290d9e5

使用RFC2104中的示例我已经完成了以下代码，我根据需要获得了COUNTER = 0的值，但是当COUNTER值设置为如上所述的2,3等其他值时，HMAC SHA1不匹配RFC 2246中的上述值。另一个问题是如果我使用memcpy和memset而不是bzero或bcopy，代码会显示一个与COUNTER = 0值不匹配的不同（错误）Hmac Sha1值。请解释为什么这个奇怪的beahviour？

    #include <openssl/evp.h>
    #include <openssl/bn.h>
    #include <openssl/sha.h>
    #include <openssl/err.h>
    #include <openssl/conf.h>
    #include <openssl/engine.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>     /* for memset() */
    #include <unistd.h>

    #define IPAD 0x36
    #define OPAD 0x5C

    #define SHA1_DIGESTLENGTH 20
    #define SHA1_BLOCK_LENGTH 64
    #define COUNTER_LENGTH 8

    typedef unsigned          char uint8_t;
    typedef unsigned short     int uint16_t;
    typedef unsigned           int uint32_t;

    /**
     * Key
     */
   #define SECRET {  0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x30  }
#define COUNTER {  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 }



void hmacsha1(){
    uint8_t key[]= SECRET;
    int key_len = sizeof(key);
    uint8_t ctr[] = COUNTER;
    unsigned char k_ipad[65];    /* inner padding -
     * key XORd with ipad
     */
    unsigned char k_opad[65];    /* outer padding -
     * key XORd with opad
     */
    int i;
    uint8_t digest[20];
    memset(digest, 0, sizeof(digest));
    /*
     * the HMAC_MD5 transform looks like:
     *
     * MD5(K XOR opad, MD5(K XOR ipad, text))
     *
     * where K is an n byte key
     * ipad is the byte 0x36 repeated 64 times
     * opad is the byte 0x5c repeated 64 times
     * and text is the data being protected
     */

    /* start out by storing key in pads */

    bzero( k_ipad, sizeof k_ipad);
    bzero( k_opad, sizeof k_opad);
    bcopy( key, k_ipad, key_len);
    bcopy( key, k_opad, key_len);

/*
    memset( k_ipad, 0, sizeof k_ipad);
    memset( k_opad, 0, sizeof k_opad);
    memcpy( key, k_ipad, key_len);
    memcpy( key, k_opad, key_len);
*/
    /* XOR key with ipad and opad values */
    for (i=0; i<64; i++) {
        k_ipad[i] ^= 0x36;
        k_opad[i] ^= 0x5c;
    }
    /*
     * perform inner MD5
     */
    EVP_MD_CTX mdctx;
    const EVP_MD *md;

    unsigned char md_value[EVP_MAX_MD_SIZE];
    unsigned int md_len;

    OpenSSL_add_all_digests();


    md = EVP_get_digestbyname("sha1");

    if(!md) {
        printf("Unknown message digest\n");
        exit(1);
    }

    EVP_MD_CTX_init(&mdctx);
    EVP_DigestInit_ex(&mdctx, md, NULL);
    EVP_DigestUpdate(&mdctx, k_ipad, 64 );
    EVP_DigestUpdate(&mdctx, ctr, 8 );
    EVP_DigestFinal_ex(&mdctx, md_value, &md_len);

    EVP_MD_CTX_init(&mdctx);
    EVP_DigestInit_ex(&mdctx, md, NULL);
    EVP_DigestUpdate(&mdctx, k_opad, 64 );
    EVP_DigestUpdate(&mdctx, md_value, md_len );
    EVP_DigestFinal_ex(&mdctx, digest, &md_len);
    EVP_MD_CTX_cleanup(&mdctx);

    printf("Digest is: ");
    for(i = 0; i < md_len; i++) printf("%02x", digest[i]);
    printf("\n");

}

Answer 1

首先，你必须做

memcpy(k_ipad, key, key_len);

memcpy(k_opad, key, key_len);

而不是

memcpy( key, k_ipad, key_len);

memcpy( key, k_opad, key_len);

在C中实现hmac sha1

1 个答案: