IOS 中的 AES 解密未给出确切结果

Question

Im trying to Decrypt my file in IOS. the file is encrypted with AES in C# application.

this is my IOS Decryption Method :

- (NSData *)AES128Operation:(CCOperation)operation key:(NSString *)key iv:(NSString *)iv
{
    NSLog(@"inside AES128Operation");
    char keyPtr[kCCKeySizeAES128 + 1];
    bzero(keyPtr, sizeof(keyPtr));
    [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];

    char ivPtr[kCCBlockSizeAES128 + 1];
    bzero(ivPtr, sizeof(ivPtr));
    if (iv) {
        [iv getCString:ivPtr maxLength:sizeof(ivPtr) encoding:NSUTF8StringEncoding];
    }

    NSUInteger dataLength = [self length];
    size_t bufferSize = dataLength + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);

    size_t numBytesEncrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(operation,
                                          kCCAlgorithmAES128,
                                          kCCOptionPKCS7Padding | kCCOptionECBMode,
                                          keyPtr,
                                          kCCBlockSizeAES128,
                                          ivPtr,
                                          [self bytes],
                                          dataLength,
                                          buffer,
                                          bufferSize,
                                          &numBytesEncrypted);

    if (cryptStatus == kCCSuccess) {
         return [NSData dataWithBytes:buffer length:numBytesEncrypted];
    }
    free(buffer);
    return nil;
}

And the way im using it :

NSString *strKey = MyKey;
NSString *strIv = MyIV;
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory , NSUserDomainMask, YES);
NSString *documentsDir = [paths objectAtIndex:0];
NSString *pathLocal_encrypted = [documentsDir stringByAppendingPathComponent:@"encrypted.file"];

NSData *data_encrpted = [[NSFileManager defaultManager] contentsAtPath:pathLocal_encrypted];

NSData *decryptedData = [data_encrpted AES128DecryptedDataWithKey:strKey iv:strIv];

IV is a 8 Byte Vector. The final decrypted file is unreadable or badly decrypted. i also tried Encrypt/Decrypt inside ios application with "AES128Operation" method on some test file and it works well but dont know why it cant decrypt the C# encrypted file.

The Decryption Works well in C# with this code (same file , Same iv , Same ,Key):

    static byte[] GetBytes(string str)
    {
        byte[] bytes = new byte[str.Length * sizeof(char)];
        System.Buffer.BlockCopy(str.ToCharArray(), 0, bytes, 0, bytes.Length);
        return bytes;
    }

    private static byte[] DecryptBytes(SymmetricAlgorithm alg, byte[] message)
    {
        if ((message == null) || (message.Length == 0))
        {
            return message;
        }
        using (var stream = new MemoryStream())
        {
            using (var decryptor = alg.CreateDecryptor())
            using (var encrypt = new CryptoStream(stream, decryptor, CryptoStreamMode.Write))
            {
                encrypt.Write(message, 0, message.Length);
                encrypt.FlushFinalBlock();
            }
            return stream.ToArray();
        }
    }
                path = openFileDialog1.FileName;
                byte[] encMessage = StreamFile(path);
                byte[] decMessage; 

                byte[] rkey = GetBytes(Mykey);
                byte[] riv = GetBytes(MyIv);
                using (var rijndael = new RijndaelManaged())
                {
                    rijndael.Key = rkey;
                    rijndael.IV = riv;
                    decMessage = DecryptBytes(rijndael, encMessage);
                }

due to answer suggestion ive tried this one to but still no hope :

    NSData *key = [NSData dataWithData:[strKey dataUsingEncoding:NSUTF8StringEncoding]];
    NSData *iv = [NSData dataWithData:[strIv dataUsingEncoding:NSUTF8StringEncoding]];
    NSData *decryptedData = [self doCipher:data_encrpted iv:iv key:key context:kCCDecrypt];

and the new function :

- (NSData *)doCipher:(NSData *)dataIn
                  iv:(NSData *)iv
                 key:(NSData *)symmetricKey
             context:(CCOperation)encryptOrDecrypt
{

    CCCryptorStatus ccStatus   = kCCSuccess;
    size_t          cryptBytes = 0;    // Number of bytes moved to buffer.
    NSMutableData  *dataOut    = [NSMutableData dataWithLength:dataIn.length + kCCBlockSizeAES128];

    ccStatus = CCCrypt( encryptOrDecrypt,
                       kCCAlgorithmAES128,
                       kCCOptionPKCS7Padding,
                       symmetricKey.bytes,
                       kCCKeySizeAES128,
                       iv.bytes,
                       dataIn.bytes,
                       dataIn.length,
                       dataOut.mutableBytes,
                       dataOut.length,
                       &cryptBytes);


        NSLog(@"CCCrypt status: %d", ccStatus);


    dataOut.length = cryptBytes;
    NSLog(@"CCCrypt ataOut.length: %d", dataOut.length);
    return dataOut;
}

this is the encryption\\decryption setting inside C# :

   public RijndaelManaged GetRijndaelManaged(string secretKey, string iv)
    {
        var keyBytes = new byte[16];
        var secretKeyBytes = Encoding.UTF8.GetBytes(secretKey);
        Array.Copy(secretKeyBytes, keyBytes, Math.Min(keyBytes.Length, secretKeyBytes.Length));

        var ivBytes = new byte[16];
        var secretIvBytes = Encoding.UTF8.GetBytes(iv);
        Array.Copy(secretIvBytes, ivBytes, Math.Min(ivBytes.Length, secretIvBytes.Length));

        return new RijndaelManaged
        {
            Mode = CipherMode.CBC,
            Padding = PaddingMode.PKCS7,
            KeySize = 128,
            BlockSize = 128,
            Key = keyBytes,
            IV = ivBytes
        };
    }

    public byte[] Encrypt(byte[] plainBytes, RijndaelManaged rijndaelManaged)
    {
        return rijndaelManaged.CreateEncryptor()
            .TransformFinalBlock(plainBytes, 0, plainBytes.Length);
    }

    public byte[] Decrypt(byte[] encryptedData, RijndaelManaged rijndaelManaged)
    {
        return rijndaelManaged.CreateDecryptor()
            .TransformFinalBlock(encryptedData, 0, encryptedData.Length);
    }

Answer 1

The iv for AES is the same as the block size: 128 bits (16 bytes), the question states: "IV is a 8 Byte Vector" which is incorrect.

Since you are using an iv the mode should be CBC but the code specifies kCCOptionECBMode , remove this, the default on iOS (Common Crypto) is CBC mode.

Note that RijndaelManaged defaults to CBC mode and PKCS#7 padding. But the key size if not explicitly set is determined by length of the key supplied and is null padded to a supported key length. It is better to explicitly set this, in RijndaelManaged use the KeySize parameter (in bits).

The block size for AES is 128 bits but RijndaelManaged supports several block sizes, AESManaged is a better choice for AES encryption. This is probably not a problem. It is better to explicitly set this, in RijndaelManaged use the BlockSize parameter with the value 128.

Answer 2

As documentation says for C# default mode (AesManaged.Mode Property):

 One of the enumeration values that specifies the block cipher mode to use for encryption. The default is CBC.

So, in ios you also must decrypt data with CBC mode.

Remove kCCOptionECBMode from your decryption code

As for padding:

Property Value Type: System.Security.Cryptography.PaddingMode One of the enumeration values that specifies the type of padding to apply. The default is PKCS7.

So, check your decryption code for correct params