Examples with EAXBlockCipher org.spongycastle.crypto.modes.EAXBlockCipher used on opensource projects

Example 1 with EAXBlockCipher

use of org.spongycastle.crypto.modes.EAXBlockCipher in project fitness-app by seemoo-lab.

the class Crypto method encryptDump.

/*
    Fitbit Flex/One/Charge firmware uses XTEA in EAX mode, we encrypt according to this.
     TODO: if we find a vulnerability for AES trackers, this method should also be able to use AES/EAX...
     Length fields must match, otherwise result can become null ...
     */
public static String encryptDump(byte[] dump, Activity activity) throws InvalidCipherTextException {
    int headerlength = 14;
    int inlength = 0;
    int plainlength = 0;
    int trailerlenght = 11;
    String outStr = "";
    byte[] header = new byte[headerlength];
    byte[] trailer = new byte[trailerlenght];
    inlength = dump.length;
    plainlength = inlength - headerlength - trailerlenght;
    byte[] plain = new byte[plainlength];
    System.arraycopy(dump, 0, header, 0, headerlength);
    System.arraycopy(dump, headerlength, plain, 0, plainlength);
    System.arraycopy(dump, inlength - trailerlenght, trailer, 0, trailerlenght);
    // Set Crypt-Byte in header
    header[4] = (byte) 0x01;
    // Nonce should not be zero... //TODO make nonce random
    // header[6] = (byte) 0xab;
    // header[7] = (byte) 0xcd;
    // get the nonce from the dump
    byte[] nonce = Arrays.copyOfRange(header, 6, 10);
    // cmac (tag) length in bytes
    int mac_len = 8 * 8;
    XTEAEngine engine = new XTEAEngine();
    EAXBlockCipher eax = new EAXBlockCipher(engine);
    Log.e(TAG, "key: " + getKey());
    Log.e(TAG, "nonce: " + Utilities.byteArrayToHexString(nonce));
    AEADParameters params = new AEADParameters(new KeyParameter(getKey()), mac_len, nonce, null);
    // TODO switch true to false here to implement a decryption method, apply it to microdumps/megadumps
    eax.init(true, params);
    byte[] result = new byte[eax.getOutputSize(plainlength)];
    int resultlength = eax.processBytes(plain, 0, plainlength, result, 0);
    eax.doFinal(result, resultlength);
    byte[] out = new byte[inlength];
    System.arraycopy(header, 0, out, 0, headerlength);
    System.arraycopy(result, 0, out, headerlength, result.length);
    System.arraycopy(header, headerlength - 4, out, headerlength + result.length, 3);
    outStr = Utilities.byteArrayToHexString(out);
    return outStr;
}