Encryption (Rijndael Cipher) With C/C++ in Android NDK

Question

I want to convert my C#(managed) decryption method into Android NDK, C/C++ (NO JAVA)

I see there was crypto. on the JAVA side but I want to keep away from any JNI, and I also see there's mcrypt and crypt++ but cant find a compiled lib for android.

Here an example in C# which I want to translate, to c/c++

    public byte[] DecryptBytes(byte[] encryptedBytes)           
    {
    RijndaelManaged RijndaelCipher = new RijndaelManaged();


            RijndaelCipher.Mode = CipherMode.CBC;

            ICryptoTransform Decryptor = RijndaelCipher.CreateDecryptor(Bytes32_KEY, Bytes16_IV);

            MemoryStream memoryStream = new MemoryStream(encryptedBytes);
            CryptoStream cryptoStream = new CryptoStream(memoryStream, Decryptor, CryptoStreamMode.Read);
            byte[] plainBytes = new byte[encryptedBytes.Length];

            int DecryptedCount = cryptoStream.Read(plainBytes, 0, plainBytes.Length);

            memoryStream.Close();
            cryptoStream.Close();

            return plainBytes;

    };

UPDATE So the best I've found so far is to use openSSL AES, I have downloaded a pre-compiled lib for Android, I'm just struggling to get it work with the example some already posted as working here is the c code example

void test_enc(){

    int keylength = 256;

    //  // 256bit KEY
        uint8_t key[32] = { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
            0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F,
            0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
            0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F};

        //128bit IV
        uint8_t iv[16] = { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
            0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F};


        //input data
        uint8_t input[64] = { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
            0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
            0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
            0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
            0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
            0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
            0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
            0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07};

    size_t inputslength = 10;
    int x;

    uint8_t *aes_key = key;

    uint8_t *aes_input = input;

    uint8_t *iv_enc = iv;
    uint8_t *iv_dec = iv;

    // buffers for encryption and decryption
    const size_t encslength = ((inputslength + AES_BLOCK_SIZE) / AES_BLOCK_SIZE) * AES_BLOCK_SIZE;
    uint8_t *enc_out = (uint8_t*)malloc(sizeof(uint8_t) *encslength);
    uint8_t *dec_out = (uint8_t*)malloc(sizeof(uint8_t) *inputslength);
    memset(enc_out, 0, encslength);
    memset(dec_out, 0, inputslength);

    // so i can do with this aes-cbc-128 aes-cbc-192 aes-cbc-256
    AES_KEY enc_key, dec_key;
    AES_set_encrypt_key(aes_key, keylength, &enc_key);
    AES_cbc_encrypt(input, enc_out, inputslength, &enc_key, iv_enc, AES_ENCRYPT);

    AES_set_decrypt_key(aes_key, keylength, &dec_key);  
    AES_cbc_encrypt(enc_out, dec_out, encslength, &dec_key, iv_dec, AES_DECRYPT);

    LOGI("Before:");
    for(x=0;x<inputslength;x++)
        LOGI("%02x, ", input[x]);

    LOGI("Encrypted:");
    for(x=0;x<encslength;x++)
        LOGI("%02x, ", enc_out[x]);

    LOGI("Decrypted:");
    for(x=0;x<encslength;x++)
        LOGI("%02x, ", dec_out[x]);
};

The encrypted bytes aren't the same as the c# and then the decrypt doesn't go back to the input, where have I gone wrong ?

I found several examples of AES under C but couldnt see where the IV would go, I then found someone posted a compiled openSSL AES for android, plus a post using the AES here [link](http://stackoverflow.com/questions/18152913/aes-aes-cbc-128-aes-cbc-192-aes-cbc-256-encryption-decryption-with-openssl-c) however the example doesnt seem to work! I shall post what I have to check my code above — RJButler, Apr 29 '15 at 14:48

RJButler · Accepted Answer · 2015-04-30T07:49:12.420

3

SOLVED:

Issue is it appears the array which held the IV gets altered after the encryption so you need to reset back before you decrypt for the result

Using the pre-built OpenSSL for Android you can find here OpenSSL-for-Android-Prebuilt

and the code above just remember to set the IV before each call to AES_cbc_encrypt.

edited Apr 30 '15 at 07:49

answered Apr 29 '15 at 18:08

RJButler

99
1
9

i need similar thing for encryption, I am not very much experienced with OpenSSL or NDK either. Can you please share some link which shows some example of using OpenSSL library in JNI folder for Android NDK ? it will be very helpful for me. – Zoombie Aug 23 '15 at 13:43

score 3 · Answer 2 · answered Jun 02 '19 at 15:49

3

OpenSSL is quite a big library (if you care about APK size)

You can use Tiny AES in C (can be used with C++)

I have added it to Android project (CMake)

https://github.com/anonym24/Android-Tiny-AES-NDK

answered Jun 02 '19 at 15:49

user924

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Encryption (Rijndael Cipher) With C/C++ in Android NDK

2 Answers2