I made 2 codes one in python and the other in android (eclipse) for encryption and decryption. Now I want to encrypt my data using python and sending it to the android to decrypt it.
How to make two different platforms to encrypt/decrypt the data?, Each platform has its own way to do the encryption and decryption? so how can i make them talk to each other and sending data and android extract the exact information which was transmitted?
Help is needed!!
If you're happy with mcrypt using AES CBC, there's a simple solution described at http://laurentcharignon.com/blog/?p=37 " Cross language Encryption/Decryption with AES CBC (Python/Java/PHP) ".
Python Code:
def encrypt_file(key, in_filename, out_filename=None, chunksize=64*1024):
if not out_filename:
out_filename = in_filename + '.enc'
iv = ''.join(chr(random.randint(0, 0xFF)) for i in range(16))
encryptor = AES.new(key, AES.MODE_CBC, iv)
filesize = os.path.getsize(in_filename)
with open(in_filename, 'rb') as infile:
with open(out_filename, 'wb') as outfile:
outfile.write(struct.pack('<Q', filesize))
outfile.write(iv)
while True:
chunk = infile.read(chunksize)
if len(chunk) == 0:
break
elif len(chunk) % 16 != 0:
chunk += ' ' * (16 - len(chunk) % 16)
outfile.write(encryptor.encrypt(chunk))
def decrypt_file(key, in_filename, out_filename=None, chunksize=24*1024):
if not out_filename:
out_filename = os.path.splitext(in_filename)[0]
with open(in_filename, 'rb') as infile:
origsize = struct.unpack('<Q', infile.read(struct.calcsize('Q')))[0]
iv = infile.read(16)
decryptor = AES.new(key, AES.MODE_CBC, iv)
with open(out_filename, 'wb') as outfile:
while True:
chunk = infile.read(chunksize)
if len(chunk) == 0:
break
outfile.write(decryptor.decrypt(chunk))
outfile.truncate(origsize)
Android Code:
public static final int SALT_LENGTH = 20;
public static final int PBE_ITERATION_COUNT = 1000;
private static final String RANDOM_ALGORITHM = "SHA1PRNG";
private static final String PBE_ALGORITHM = "PBEWithSHA256And256BitAES-CBC-BC";
private static final String CIPHER_ALGORITHM = "AES/CBC/PKCS5Padding";
private static final String TAG = Act.class.getSimpleName();
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
try {
String password = "password";
String plainText = "plaintext message to be encrypted";
// byte[] salt = generateSalt();
byte[] salt = "dfghjklpoiuytgftgyhj".getBytes();
Log.i(TAG, "Salt: " + salt.length + " " + HexEncoder.toHex(salt));
PBEKeySpec pbeKeySpec = new PBEKeySpec(password.toCharArray(), salt, PBE_ITERATION_COUNT, 256);
SecretKeyFactory factory = SecretKeyFactory.getInstance(PBE_ALGORITHM);
SecretKey tmp = factory.generateSecret(pbeKeySpec);
SecretKey secret = new SecretKeySpec(tmp.getEncoded(), "AES");
byte[] key = secret.getEncoded();
Log.i(TAG, "Key: " + HexEncoder.toHex(key));
// PBEParameterSpec pbeParamSpec = new PBEParameterSpec(salt, ITERATION_COUNT);
Cipher encryptionCipher = Cipher.getInstance(CIPHER_ALGORITHM);
// byte[] encryptionSalt = generateSalt();
// Log.i(TAG, "Encrypted Salt: " + encryptionSalt.length + " " + HexEncoder.toHex(encryptionSalt));
// PBEParameterSpec pbeParamSpec = new PBEParameterSpec(encryptionSalt, 1000);
// byte[] iv = params.getParameterSpec(IvParameterSpec.class).getIV();
Log.i(TAG, encryptionCipher.getParameters() + " ");
byte[] iv = generateIv();
IvParameterSpec ivspec = new IvParameterSpec(iv);
encryptionCipher.init(Cipher.ENCRYPT_MODE, secret, ivspec);
byte[] encryptedText = encryptionCipher.doFinal(plainText.getBytes());
Log.i(TAG, "Encrypted: " + HexEncoder.toHex(encryptedText));
Cipher decryptionCipher = Cipher.getInstance(CIPHER_ALGORITHM);
decryptionCipher.init(Cipher.DECRYPT_MODE, secret, ivspec);
byte[] decryptedText = decryptionCipher.doFinal(encryptedText);
Log.i(TAG, "Decrypted: " + new String(decryptedText));
} catch (Exception e) {
e.printStackTrace();
}
}
private byte[] generateSalt() throws NoSuchAlgorithmException {
SecureRandom random = SecureRandom.getInstance(RANDOM_ALGORITHM);
byte[] salt = new byte[SALT_LENGTH];
random.nextBytes(salt);
return salt;
}
private byte[] generateIv() throws NoSuchAlgorithmException {
SecureRandom random = SecureRandom.getInstance(RANDOM_ALGORITHM);
byte[] iv = new byte[16];
random.nextBytes(iv);
return iv;
}
}
TLS could be used to securely transmit data in a compatible way.
If additionally you use http protocol for the communication then there are already high-level libraries that might hide all gory details from you; just provide client/server certificates and make appropriate requests.
It might save you from reimplementing poorly many security features such as forward secrecy .
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