AES encryption makes different result in iOS and Android

Question

Trying to encrypt sample data using AES128 algorithm with CBC and PKCS7 padding in Android and iOS, but results are different :(

Android code:

private static final byte[] KEY = { 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x10};

int srcBuffSiz = 1024;
byte[] srcBuff = new byte[srcBuffSiz];
Arrays.fill(srcBuff, (byte)0x01);

SecretKeySpec skeySpec = new SecretKeySpec(KEY, "AES");
Cipher ecipher = Cipher.getInstance("AES/CBC/PKCS7Padding");
ecipher.init(Cipher.ENCRYPT_MODE, skeySpec);
byte[] dstBuff = ecipher.doFinal(srcBuff);
int bytesEncrypted = dstBuff.length;

iOS Code:

    // Source buffer
    size_t srcBuffSiz = 1024;
    unsigned char* srcBuff = new unsigned char[srcBuffSiz];
    memset(srcBuff, 0x01, srcBuffSiz);

    // Destination buffer
    size_t dstBuffSiz = srcBuffSiz + 128;
    unsigned char* dstBuff = new unsigned char[dstBuffSiz];
    memset(dstBuff, 0x00, dstBuffSiz);

    unsigned char keyPtr[kCCKeySizeAES128] = { 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x10};

    size_t bytesEncrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding,
                                          keyPtr, kCCKeySizeAES128,
                                          NULL /* initialization vector (optional) */,
                                          srcBuff, srcBuffSiz, /* input */
                                          dstBuff, dstBuffSiz, /* output */
                                          &bytesEncrypted);

So, in both cases I'm trying to encrypt sample 1024 bytes buffer (previosly filled with 0x01 values) using predefined sample key.

First and last 6 bytes of encrypted buffer in iOS:

ED CC 64 27 A8 99 ... 0C 44 9F EC 34 FC

First and last 6 bytes of encrypted buffer in Android:

AE 65 A9 F7 7F 0E ... 1F BD AE 8B 85 ED

Any idea?

If i replace Cipher.getInstance("AES/CBC/PKCS7Padding") to Cipher.getInstance("AES"), then first several bytes of encrypted buffer will be the same, but from 17th byte ...

iOS:

ED CC 64 27 A8 99 DA 83 D5 4A B0 03 0F E7 DD A7 35 F2 50 5C 49 47 CC 3B 2F AB D1 61 05

Android:

ED CC 64 27 A8 99 DA 83 D5 4A B0 03 0F E7 DD A7 ED CC 64 27 A8 99 DA 83 D5 4A B0 03 0F

have u tried to decrypt the result of another phone? say, android decrypt iOS result and iOS try Android result? — dumbfingers
No, i haven't. I thought an encryption result should be the same. — Tutankhamen
unsigned char array VS a byte array.. don't you think something is different between these? :) — Anders Metnik
You should try decrypt those result to see if they are the same. Because even you use the same key to encrypt the result can be different. That's the purpose of encryption. If everytime u use the same key get the same result, it's not collision safe. See this: stackoverflow.com/questions/11818684/… — dumbfingers
ss1271: I don't use any salt in my code, so, the result can't different. — Tutankhamen

Vit Khudenko Vit Khudenko · Accepted Answer · 2012-10-24T08:51:56

I vaguely recall I had once similar issue of "synchronizing" the encryption between Android and iPhone, and the solution was in proper IV (initialization vector) usage. So probably switching on an explicit IV usage in Android could help:

final byte[] iv = new byte[16];
Arrays.fill(iv, (byte) 0x00);
IvParameterSpec ivParameterSpec = new IvParameterSpec(iv);
.. // the rest of preparations
ecipher.init(Cipher.ENCRYPT_MODE, skeySpec, ivParameterSpec);

Because when on iPhone you pass NULL as the IV, it may internally use a default one that corresponds to the just stated above.

But in production environment you should use a (cryptographically secure pseudo-)random initialization vector, stored together with the data. Then it is safe for all modes of operations. [1]

AES encryption makes different result in iOS and Android

2 Answers