Hello:
Try this code.
import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.math.BigInteger;
import java.util.Arrays;
/**
* Created by dalvarez on 3/14/17.
*/
public class Encryption {
/**
* String keyhex
*
* @throws Exception
*/
static byte[] encrypt(String keyhex, String data) throws Exception {
// fixed key; in real use key should be securely provided or generated
// crude way of converting hex to bytes, better ways are possible
byte[] key = new BigInteger (keyhex,16).toByteArray();
if( key.length > 16 ) key = Arrays.copyOfRange (key, 1, key.length); // maybe signed
if( key.length != 16 ) throw new Exception ("key length wrong!");
// all-zero IV, only secure if key is unique every time
byte[] IV = new byte[16];
// fixed plaintext for example, in real use obtain as needed
byte[] plainbytes = data.getBytes();
// note: for ASCII-only data the Java default encoding is okay;
// if real data can or could contain other chars, specify a
// suitable encoding; "UTF-8" is good for most text-y data
// ENCRYPT: we need to add zero padding ourself since JCE doesn't do that
// Java makes this easy because arrays are initialized to all-zeros
if( plainbytes.length %16 !=0 )
plainbytes = Arrays.copyOf (plainbytes, (plainbytes.length /16 +1)*16);
Cipher aes = Cipher.getInstance ("AES/CBC/NoPadding");
aes.init (Cipher.ENCRYPT_MODE, new SecretKeySpec(key, "AES"), new IvParameterSpec(IV));
byte[] cipherbytes = aes.doFinal (plainbytes);
// crude way of converting bytes to hex, again better possible
return cipherbytes;
// alternatively just write to a file and let other tools handle
}
public static String decrypt(String keyhex, byte[] cipherbytes) throws Exception {
// crude way of converting hex to bytes, better ways are possible
byte[] key = new BigInteger (keyhex,16).toByteArray();
if( key.length > 16 ) key = Arrays.copyOfRange (key, 1, key.length); // maybe signed
if( key.length != 16 ) throw new Exception ("key length wrong!");
// all-zero IV, only secure if key is unique every time
byte[] IV = new byte[16];
// DECRYPT: assuming bytes read from file, or already converted from hex
//same as above: Cipher aes = Cipher.getInstance ("AES/CBC/NoPadding");
Cipher aes = Cipher.getInstance ("AES/CBC/NoPadding");
aes.init (Cipher.DECRYPT_MODE, new SecretKeySpec (key, "AES"), new IvParameterSpec (IV));
byte[] resultbytes = aes.doFinal (cipherbytes);
// now we need to remove the zero padding, which is ambiguous
// this will damage data that actually has trailing zero bytes
int i; for( i = resultbytes.length; --i>=0 && resultbytes[i]==0; ){}
resultbytes = Arrays.copyOf (resultbytes, i+1);
// for example just display, for real use adapt as desired
// see above about encoding
return new String (resultbytes);
}
public static void main(String[] arg) {
try {
byte[] cipherbytes = Encryption.encrypt("6c616d70736865657031323334353637", "Hello world");
System.out.println ("encrypt hex->" + new BigInteger(1, cipherbytes).toString(16));
String decript = Encryption.decrypt("6c616d70736865657031323334353637", cipherbytes);
System.out.println ("decrypt chars->" + decript);
} catch (Exception e) {
e.printStackTrace();
}
}
}
Mark.
Stephen. Reason: typo
