在目标 c 中，如何使用 md5 作为密钥进行 AES256 加密？

Question

我一直在尝试复制一个使用 md5 作为密钥进行 AES256 加密的 android 代码。一切似乎都很好，但加密后的值似乎不一样。请通过我的以下代码

安卓：-

public static String encrypt(String key, String value) {
    try {
        byte[] keyArr = new byte[32];
        MessageDigest md = MessageDigest.getInstance("MD5");
        byte[] hash = md.digest(key.getBytes("US-ASCII"));//in md5 function 1st line
        keyArr = arrayCopy(0, hash, 0, keyArr, 16);//in md5 function 1st for loop
        keyArr = arrayCopy(0, hash, 15, keyArr, 16);//in md5 function 2nd for loop
        SecretKeySpec skeySpec = new SecretKeySpec(keyArr, "AES");
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
        byte[] encrypted = cipher.doFinal(value.getBytes());
        String encryptedB64 = new String(Base64.encode(encrypted, Base64.DEFAULT));
        return encryptedB64;
    } catch (Exception ex) {
        ex.printStackTrace();
    }
    return null;
}
private static byte[] arrayCopy(int sourceIndex,byte[] source,int targetIndex,byte[] target,int transferSize){
    if(!(transferSize >0))
        return null;
    if(sourceIndex>=0 && sourceIndex < source.length){
        int transferCnt=0;
        int i=sourceIndex;
        for(int j=targetIndex;;j++,i++){
            if(targetIndex>=target.length || sourceIndex>=source.length || (++transferCnt>transferSize)){
                break;
            }
            target[j] = source[i];
        }
    }else{
        return null;
    }
    return target;
}

iOS 目标-c

+ (NSString *) getFalconEncryptedValueForKey:(NSString *)theKey forString:(NSString *)theString
{
    char keyPtr[kCCKeySizeAES256+1]; // room for terminator (unused)
    bzero(keyPtr, sizeof(keyPtr)); // fill with zeroes (for padding)
    NSData *rawData = [theString dataUsingEncoding:NSUTF8StringEncoding];
    NSString *md5Key = [self md5:theKey];
    [md5Key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
    NSUInteger dataLength = [rawData length];
    size_t bufferSize = dataLength + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);
    size_t numBytesEncrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding + kCCOptionECBMode,
                                          keyPtr, kCCKeySizeAES256,
                                          NULL /* initialization vector (optional) */,
                                          [rawData bytes], dataLength, /* input */
                                          buffer, bufferSize, /* output */
                                          &numBytesEncrypted);
    if (cryptStatus == kCCSuccess)
    {
        NSData *tempData = [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
        NSString* encrypted64 = [tempData base64EncodedStringWithOptions:0];//Even i have tried base 64 encding with other options available
        return encrypted64;
    }

    free(buffer); //free the buffer;
    return nil;
}


+ (NSString *) md5:(NSString *) input
{
//    const char * pointer = [self UTF8String];
    const char *cStr = [input cStringUsingEncoding:NSASCIIStringEncoding];
    unsigned char result[CC_MD5_DIGEST_LENGTH];
    CC_MD5( cStr, (CC_LONG)strlen(cStr), result );

    NSMutableString *md5String = [NSMutableString stringWithCapacity:CC_MD5_DIGEST_LENGTH * 2];
    for (int i = 0; i < CC_MD5_DIGEST_LENGTH; i++)
        [md5String appendFormat:@"%02x",result[i]];
    for (int i = 0; i < CC_MD5_DIGEST_LENGTH; i++)
        [md5String appendFormat:@"%02x",result[i]];

    return md5String;
    //for 32 byte. md5 produces only 16 byte info. we are replicating it again to make it 32 byte for aes256
}

任何对我做错的方向的指导都会非常有帮助。提前致谢

Answer 1

AES256加密使用md5加倍作为密钥

不，事实并非如此。

在 Android 中，keyArr 中第一个 hash 的最后一个字节被第二个 hash 覆盖（更准确地说是第二个 hash 的第一个字节）。所以keyArr的最后一个字节总是0。

我不精通Objective-C，但我认为，应该这样做：

NSMutableString *md5String = [NSMutableString stringWithCapacity:CC_MD5_DIGEST_LENGTH * 2];
for (int i = 0; i < CC_MD5_DIGEST_LENGTH-1; i++)
    [md5String appendFormat:@"%02x",result[i]];
for (int i = 0; i < CC_MD5_DIGEST_LENGTH; i++)
    [md5String appendFormat:@"%02x",result[i]];
[md5String appendFormat:@"%02x",0];

（顺便说一句，arrayCopy 可以产生一个 IndexOutOfBoundsException，尽管它进行了多次检查）。

当然，这会生成一个长度为 64 个字符的十六进制编码字符串。这不是你想要的。相反，您应该生成长度为 32 的实际字节。

正确的代码（由 OP 提供）

+ (NSString *) getEncryptedValueWithKey:(NSString *)theKey forString:(NSString *)theString
{
    NSData *rawData = [theString dataUsingEncoding:NSUTF8StringEncoding];

    unsigned char md5Buffer[kCCKeySizeAES256+1];
    memset(md5Buffer, 0, kCCKeySizeAES256+1);
    const char *cStr = [theKey UTF8String];

    // do md5 hashing
    CC_MD5(cStr, CC_MD5_DIGEST_LENGTH, md5Buffer);

    unsigned char lastChar = md5Buffer[15];
    for (NSInteger i = 15; i <= 30; i++) {
        md5Buffer[i] = md5Buffer[i-15];
    }
    md5Buffer[30] = lastChar;
    //MD5 key obtaining end

    NSUInteger dataLength = [rawData length];
    size_t bufferSize = dataLength + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);
    size_t numBytesEncrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding + kCCOptionECBMode, md5Buffer, kCCKeySizeAES256, NULL /* initialization vector (optional) */, [rawData bytes], dataLength, /* input */ buffer, bufferSize, /* output */ &numBytesEncrypted);
    if (cryptStatus == kCCSuccess)
    {
        NSData *tempData = [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
        NSString* encrypted64 = [tempData base64EncodedStringWithOptions:0];//Even i have tried base 64 encding with other options available
        return encrypted64;
    }

    free(buffer); //free the buffer;
    return nil;
}