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## com.knowgate.misc
Class TEA

    java.lang.Object
      com.knowgate.misc.TEA

    public class TEA

extends java.lang.Object

Tiny Encryption Algorithm.

(The following description is from the web page for the C and Assembler source code at University of Bradford Yorkshire, England - The Cryptography & Computer Communications Security Group) The description is used with the permission of the authors, Dr S J Shepherd and D A G Gillies.

The Tiny Encryption Algorithm is one of the fastest and most efficient cryptographic algorithms in existence. It was developed by David Wheeler and Roger Needham at the Computer Laboratory of Cambridge University. It is a Feistel cipher which uses operations from mixed (orthogonal) algebraic groups - XORs and additions in this case. It encrypts 64 data bits at a time using a 128-bit key. It seems highly resistant to differential cryptanalysis, and achieves complete diffusion (where a one bit difference in the plaintext will cause approximately 32 bit differences in the ciphertext) after only six rounds. Performance on a modern desktop computer or workstation is very impressive.

TEA takes 64 bits of data in v[0] and v[1], and 128 bits of key in k[0] - k[3]. The result is returned in w[0] and w[1]. Returning the result separately makes implementation of cipher modes other than Electronic Code Book a little bit easier.

TEA can be operated in any of the modes of DES.

n is the number of iterations. 32 is ample, 16 is sufficient, as few as eight should be OK for most applications, especially ones where the data age quickly (real-time video, for example). The algorithm achieves good dispersion after six iterations. The iteration count can be made variable if required.

Note this algorithm is optimised for 32-bit CPUs with fast shift capabilities. It can very easily be ported to assembly language on most CPUs.

delta is chosen to be the Golden ratio ((5/4)1/2 - 1/2 ~ 0.618034) multiplied by 232. On entry to decipher(), sum is set to be delta * n. Which way round you call the functions is arbitrary: DK(EK(P)) = EK(DK(P)) where EK and DK are encryption and decryption under key K respectively.

Translator's notes:

- Although the this algorithm is optimised for 32-bit CPUs with fast shift capabilities Java manages to throw it all away by not providing unsigned values resulting in the excessive use of AND's to prevent sign extension on promotion of a byte to an integer.

- The following description is taken from the Mach5 Software cryptography archives at www.mach5.com/crypto.

  Tiny Encryption Algorithm (TEA)
  TEA is a cryptographic algorithm designed to minimize memory footprint, and maximize speed. However, the cryptographers from Counterpane Systems have discovered three related-key attacks on TEA, the best of which requires only 223 chosen plaintexts and one related key query. The problems arise from the overly simple key schedule. Each TEA key can be found to have three other equivalent keys, as described in a paper by David Wagner, John Kelsey, and Bruce Schneier. This precludes the possibility of using TEA as a hash function. Roger Needham and David Wheeler have proposed extensions to TEA that counters the above attacks.

Example of use:

     byte key[] = new BigInteger("39e858f86df9b909a8c87cb8d9ad599", 16).toByteArray();
     TEA t = new TEA(key);

     String src = "hello world!";
     System.out.println("input = " + src);
     byte plainSource[] = src.getBytes();
     int enc[] = t.encode(plainSource, plainSource.length);
     System.out.println(t.padding() + " bytes added as padding.");
     byte dec[] = t.decode(enc);
     System.out.println("output = " + new String(dec));

Since:
  JDK1.1

Constructor Summary
`TEA(byte[] key)` Accepts key for enciphering/deciphering.

Method Summary
`byte[]` | `decipher(byte[] v)` Decipher two `bytes`s.
`int[]` | `decipher(int[] v)` Decipher two `int`s.
`byte[]` | `decode(byte[] b, int count)` Convert a byte array to ints and then decode.
`byte[]` | `decode(int[] b)` Decode an integer array.
`byte[]` | `encipher(byte[] v)` Encipher two `bytes`s.
`int[]` | `encipher(int[] v)` Encipher two `int`s.
`int[]` | `encode(byte[] b, int count)` Byte wrapper for encoding.
`static void` | `main(java.lang.String[] args)` Encodes and decodes "Hello world!"
`int` | `padding()` Report how much padding was done in the last encode.
`java.lang.String` | `toString()` Representation of TEA class

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

Constructor Detail

### TEA

    public TEA(byte[] key)

  Accepts key for enciphering/deciphering.

  Parameters:
    `key` - 128 bit (16 byte) key.
  Throws:
    `java.lang.ArrayIndexOutOfBoundsException` - if the key isn't the correct length.

Method Detail

### main

    public static void main(java.lang.String[] args)

  Encodes and decodes "Hello world!" for your personal pleasure.

### toString

    public java.lang.String toString()

  Representation of TEA class

  Overrides:
    `toString` in class `java.lang.Object`

### encipher

    public int[] encipher(int[] v)

  Encipher two `int`s. Replaces the original contents of the parameters with the results. The integers are usually created from 8 bytes. The usual way to collect bytes to the int array is:

       byte ba[] = { .... };
       int v[] = new int[2];
       v[0] = (ba[j] << 24 ) | (((ba[j+1])&0xff) << 16) | (((ba[j+2])&0xff) << 8) | ((ba[j+3])&0xff);
       v[1] = (ba[j+4] << 24 ) | (((ba[j+5])&0xff) << 16) | (((ba[j+6])&0xff) << 8) | ((ba[j+7])&0xff);
       v = encipher(v);

  Parameters:
    `v` - two `int` array as input.
  Returns:
    array of two `int`s, enciphered.

### decipher

    public int[] decipher(int[] v)

  Decipher two `int`s. Replaces the original contents of the parameters with the results. The integers are usually decocted to 8 bytes. The decoction of the `int`s to bytes can be done this way.

       int x[] = decipher(ins);
       outb[j]   = (byte)(x[0] >>> 24);
       outb[j+1] = (byte)(x[0] >>> 16);
       outb[j+2] = (byte)(x[0] >>> 8);
       outb[j+3] = (byte)(x[0]);
       outb[j+4] = (byte)(x[1] >>> 24);
       outb[j+5] = (byte)(x[1] >>> 16);
       outb[j+6] = (byte)(x[1] >>> 8);
       outb[j+7] = (byte)(x[1]);

  Parameters:
    `v` - `int` array of 2
  Returns:
    deciphered `int` array of 2

### encipher

    public byte[] encipher(byte[] v)

  Encipher two `bytes`s.

  Parameters:
    `v` - `byte` array of 2
  Returns:
    enciphered `byte` array of 2

### decipher

    public byte[] decipher(byte[] v)

  Decipher two `bytes`s.

  Parameters:
    `v` - `byte` array of 2
  Returns:
    decipherd `byte` array of 2

### encode

    public int[] encode(byte[] b,
                        int count)

  Byte wrapper for encoding. Converts bytes to ints. Padding will be added if required.

  Parameters:
    `b` - incoming `byte` array
    `byte` - count
  Returns:
    integer conversion array, possibly with padding.
  See Also:
    `padding()`

### padding

    public int padding()

  Report how much padding was done in the last encode.

  Returns:
    bytes of padding added
  See Also:
    `encode(byte[], int)`

### decode

    public byte[] decode(byte[] b,
                         int count)

  Convert a byte array to ints and then decode. There may be some padding at the end of the byte array from the previous encode operation.

  Parameters:
    `b` - bytes to decode
    `count` - number of bytes in the array to decode
  Returns:
    `byte` array of decoded bytes.

### decode

    public byte[] decode(int[] b)

  Decode an integer array. There may be some padding at the end of the byte array from the previous encode operation.

  Parameters:
    `b` - bytes to decode
    `count` - number of bytes in the array to decode
  Returns:
    `byte` array of decoded bytes.

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