hmac－md5算法

+ (NSString *)hmac_MD5:(NSString *)plaintext withKey:(NSString *)key
{
    constchar *cKey  = [key cStringUsingEncoding:NSUTF8StringEncoding];
    constchar *cData = [plaintext cStringUsingEncoding:NSUTF8StringEncoding];
    constunsigned int blockSize =64;   //散列函數的分割數據長度爲64
    char ipad[blockSize];
    char opad[blockSize];
    char keypad[blockSize];
    
    unsignedint keyLen = strlen(cKey); //密鑰的長度
    CC_MD5_CTX ctxt;
    if (keyLen > blockSize) {  //密鑰長度大於分割數據長度，則先進行md5運算，運算結果拷貝到keypad中
        CC_MD5_Init(&ctxt);
        CC_MD5_Update(&ctxt, cKey, keyLen);
        CC_MD5_Final((unsignedchar *)keypad, &ctxt);
        keyLen = CC_MD5_DIGEST_LENGTH;  //使keylength爲16字節
    }
    else {
        memcpy(keypad, cKey, keyLen);  //否則直接拷貝到keypad字符串中
    }
    
    memset(ipad,0x36, blockSize);  //設置ipad爲0x36
    memset(opad,0x5c, blockSize);  //設置opad爲0x5c
    
    int i;
    for (i =0; i < keyLen; i++) {
        ipad[i] ^= keypad[i];   //keypad與ipad做異或運算
        opad[i] ^= keypad[i];   //可以pad與opad做異或運算
    }
    
    //將ipad加入到ctxt中，再將cdata加入到ctxt中，進行md5運算,結果放入md5字符串中
    CC_MD5_Init(&ctxt);
    CC_MD5_Update(&ctxt, ipad, blockSize);
    CC_MD5_Update(&ctxt, cData,strlen(cData));
    unsignedchar md5[CC_MD5_DIGEST_LENGTH];
    CC_MD5_Final(md5, &ctxt);
    
    //將opad加入到ctxt中，再將上一步的md5加入到ctxt中，進行md5運算，結果放入md5字符串中
    CC_MD5_Init(&ctxt);
    CC_MD5_Update(&ctxt, opad, blockSize);
    CC_MD5_Update(&ctxt, md5,CC_MD5_DIGEST_LENGTH);
    CC_MD5_Final(md5, &ctxt);
    
    //轉成16進制
    constunsigned int hex_len =CC_MD5_DIGEST_LENGTH*2+2;
    char hex[hex_len];
    for(i =0; i < CC_MD5_DIGEST_LENGTH; i++) {
        snprintf(&hex[i*2], hex_len-i*2,"%02x", md5[i]);
    }
    
    NSData *HMAC = [[NSDataalloc] initWithBytes:hexlength:strlen(hex)];
    NSString *hash = [[NSStringalloc] initWithData:HMACencoding:NSUTF8StringEncoding];
    
    return hash;
}