/**
* AES CBC decrypt.
*
* @param civ the cipher text, iv, and mac
* @param secretKeys the AES & HMAC keys
* @return The raw decrypted bytes
* @throws GeneralSecurityException if MACs don't match or AES is not implemented
*/
public static byte[] decrypt(CipherTextIvMac civ, SecretKeys secretKeys)
throws GeneralSecurityException {
byte[] ivCipherConcat = CipherTextIvMac.ivCipherConcat(civ.getIv(), civ.getCipherText());
byte[] computedMac = generateMac(ivCipherConcat, secretKeys.getIntegrityKey());
if (constantTimeEq(computedMac, civ.getMac())) {
Cipher aesCipherForDecryption = Cipher.getInstance(CIPHER_TRANSFORMATION);
aesCipherForDecryption.init(
Cipher.DECRYPT_MODE,
secretKeys.getConfidentialityKey(),
new IvParameterSpec(civ.getIv()));
return aesCipherForDecryption.doFinal(civ.getCipherText());
} else {
throw new GeneralSecurityException("MAC stored in civ does not match computed MAC.");
}
}
/**
* Generates a random IV and encrypts this plain text with the given key. Then attaches a hashed
* MAC, which is contained in the CipherTextIvMac class.
*
* @param plaintext The text that will be encrypted
* @param secretKeys The combined AES & HMAC keys with which to encrypt
* @return a tuple of the IV, ciphertext, mac
* @throws GeneralSecurityException if AES is not implemented on this system
*/
public static CipherTextIvMac encrypt(byte[] plaintext, SecretKeys secretKeys)
throws GeneralSecurityException {
byte[] iv = generateIv();
Cipher aesCipherForEncryption = Cipher.getInstance(CIPHER_TRANSFORMATION);
aesCipherForEncryption.init(
Cipher.ENCRYPT_MODE, secretKeys.getConfidentialityKey(), new IvParameterSpec(iv));
/*
* Now we get back the IV that will actually be used. Some Android
* versions do funny stuff w/ the IV, so this is to work around bugs:
*/
iv = aesCipherForEncryption.getIV();
byte[] byteCipherText = aesCipherForEncryption.doFinal(plaintext);
byte[] ivCipherConcat = CipherTextIvMac.ivCipherConcat(iv, byteCipherText);
byte[] integrityMac = generateMac(ivCipherConcat, secretKeys.getIntegrityKey());
return new CipherTextIvMac(byteCipherText, iv, integrityMac);
}
/**
* Converts the given AES/HMAC keys into a base64 encoded string suitable for storage. Sister
* function of keys.
*
* @param keys The combined aes and hmac keys
* @return a base 64 encoded AES string & hmac key as base64(aesKey) : base64(hmacKey)
*/
public static String keyString(SecretKeys keys) {
return keys.toString();
}
