I was looking for quick way to 'encrypt' an integer into another integer.  I tried a few things:

I tried using Java Ciphers with 32-bit block size ( ex. "DES/OFB32/NoPadding")

I couldn't make Ciphers work.  The encrypted integers that were returned were not sufficiently distributed in the integer domain....probably because I was doing something wrong... I didn't have time to figure it out.  See java code snippet at the bottom of the message.

I found this code snipped implementing a Fiestel Network

http://wiki.postgresql.org/wiki/Pseudo_encrypt

I made the changes recommended by J. Jancar to implement this:

-- Function: pseudo_encrypt(integer)

-- DROP FUNCTION pseudo_encrypt(integer);

CREATE OR REPLACE FUNCTION pseudo_encrypt(value integer)
  RETURNS integer AS
$BODY$
DECLARE
l1 int;
l2 int;
r1 int;
r2 int;
i int:=0;
BEGIN
 l1:= (VALUE >> 16) & 65535;
 r1:= VALUE & 65535;
 WHILE i < 3 LOOP
   l2 := r1;
   r2 := l1 # ((((1366.0 * r1 + 150889) % 714025) / 714025.0) * 32767)::int;
   l1 := l2;
   r1 := r2;
   i := i + 1;
 END LOOP;
 RETURN ((r1 << 16) + l1);
END;
$BODY$
  LANGUAGE plpgsql IMMUTABLE STRICT
  COST 100;
ALTER FUNCTION pseudo_encrypt(integer)
  OWNER TO thyroid;




Tested x = f(f(x)) on 4 million positive integers, works.

Translated to Java:

    public static int pseudoEncrypt(int data) {
        int l1 = (data >> 16) & 65535;
        int r1 = data & 65535;
        for (int i = 0; i<3 br="" i="">            int l2 = r1;
            //Don't change these constants until and unless we understand this better
            int r2 = l1 ^ (int)((((1366.0 * r1 + 150889) % 714025) / 714025.0) * 32767);
            l1 = l2;
            r1 = r2;
        }
        return (r1 << 16) + l1;
    }

Tested x = f(f(x))Java integers.  Works.




    @Test
    public void test3() throws Exception {
        for (int i=0; i<1000 br="" i="">       
            final String keyString = "YKQ22ROLDQYU6===";
            final String ivParametersString = "TOSHCB6GRJBLC===";
           
            byte[] data = ByteBuffer.allocate(4).putInt(i).array();
   
            SecretKey secretKey = new SecretKeySpec(base32.decode(keyString), "DES");
            final IvParameterSpec iv = new IvParameterSpec(base32.decode(ivParametersString));
            Cipher cipher = Cipher.getInstance("DES/OFB32/NoPadding");
       
            cipher.init(Cipher.ENCRYPT_MODE, secretKey, iv);
            //IvParameterSpec iv = new IvParameterSpec(base32.decode(ivDataString));
            byte[] encryptedData = cipher.doFinal(data);
            int intEncrypted = ByteBuffer.wrap(encryptedData).getInt();
           
            cipher.init(Cipher.DECRYPT_MODE, secretKey, iv);
            byte[] decryptedData = cipher.doFinal(encryptedData);
   
            Assert.assertArrayEquals(data, decryptedData);
            int intDecrypted = ByteBuffer.wrap(decryptedData).getInt();
            System.out.printf("%s %s %s%n", i, intEncrypted, intDecrypted);
        }
    }

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