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`java.lang.Object`

`gnu.javax.crypto.cipher.BaseCipher`

`gnu.javax.crypto.cipher.Cast5`

**Implemented Interfaces:**- Cloneable, IBlockCipher, gnu.javax.crypto.cipher.IBlockCipherSpi

`public class `**Cast5**

`extends BaseCipher`

An implmenetation of the *RFC-2144*, dated May 1997.

`CAST5`

(a.k.a. CAST-128) algorithm,
as per
In this RFC, *Carlisle Adams* (the CA in CAST, ST stands for
*Stafford Tavares*) describes CAST5 as:

"...a DES-like Substitution-Permutation Network (SPN) cryptosystem which appears to have good resistance to differential cryptanalysis, linear cryptanalysis, and related-key cryptanalysis. This cipher also possesses a number of other desirable cryptographic properties, including avalanche, Strict Avalanche Criterion (SAC), Bit Independence Criterion (BIC), no complementation property, and an absence of weak and semi-weak keys."

`CAST5`

is a symmetric block cipher with a block-size of 8
bytes and a variable key-size of up to 128 bits. Its authors, and their
employer (Entrust Technologies, a Nortel majority-owned company), made it
available worldwide on a royalty-free basis for commercial and non-commercial
uses.

The `CAST5`

encryption algorithm has been designed to allow a
key size that can vary from `40`

bits to `128`

bits,
in 8-bit increments (that is, the allowable key sizes are ```
40, 48, 56,
64, ..., 112, 120,
```

and `128`

bits. For variable keysize
operation, the specification is as follows:

- For key sizes up to and including
`80`

bits (i.e.,`40, 48, 56, 64, 72,`

and`80`

bits), the algorithm is exactly as specified but uses`12`

rounds instead of`16`

; - For key sizes greater than
`80`

bits, the algorithm uses the full`16`

rounds; - For key sizes less than
`128`

bits, the key is padded with zero bytes (in the rightmost, or least significant, positions) out to`128`

bits (since the`CAST5`

key schedule assumes an input key of`128`

bits).

References:

## Field Summary

### Fields inherited from class gnu.javax.crypto.cipher.BaseCipher

`currentBlockSize`

,`currentKey`

,`defaultBlockSize`

,`defaultKeySize`

,`lock`

,`name`

### Fields inherited from interface gnu.javax.crypto.cipher.IBlockCipher

`CIPHER_BLOCK_SIZE`

,`KEY_MATERIAL`

## Constructor Summary

`Cast5()`

- Trivial 0-arguments constructor.

## Method Summary

`Iterator<E>`

`blockSizes()`

- Returns an
`Iterator`

over the supported block sizes.

`Object`

`clone()`

- Returns a clone of this instance.

`void`

`void`

`Iterator<E>`

`Object`

`makeKey(byte[] uk, int bs)`

- Expands a user-supplied key material into a session key for a designated
*block size*.

`boolean`

`selfTest()`

- A
*correctness*test that consists of basic symmetric encryption / decryption test(s) for all supported block and key sizes, as well as one (1) variable key Known Answer Test (KAT).

### Methods inherited from class gnu.javax.crypto.cipher.BaseCipher

`clone`

,`currentBlockSize`

,`decryptBlock`

,`defaultBlockSize`

,`defaultKeySize`

,`encryptBlock`

,`init`

,`name`

,`reset`

,`selfTest`

,`testKat`

,`testKat`

### Methods inherited from class java.lang.Object

`clone`

,`equals`

,`extends Object> getClass`

,`finalize`

,`hashCode`

,`notify`

,`notifyAll`

,`toString`

,`wait`

,`wait`

,`wait`

public Iterator<E> blockSizes()

Returns an`Iterator`

over the supported block sizes. Each element returned by this object is an`Integer`

.

Specified by:- blockSizes in interface IBlockCipher
- blockSizes in interface gnu.javax.crypto.cipher.IBlockCipherSpi

Returns:- an
`Iterator`

over the supported block sizes.

public Object clone()

Returns a clone of this instance.

Specified by:- clone in interface IBlockCipher

Overrides:- clone in interface BaseCipher

Returns:- a clone copy of this instance.

public void decrypt(byte[] in, int i, byte[] out, int j, Object k, int bs)

Decrypts exactly one block of ciphertext.

Specified by:- decrypt in interface gnu.javax.crypto.cipher.IBlockCipherSpi

Parameters:`in`

- the ciphertext.`out`

- the plaintext.`k`

- the session key to use.`bs`

- the block size to use.

Throws:`IllegalArgumentException`

- if the block size is invalid.`ArrayIndexOutOfBoundsException`

- if there is not enough room in either the plaintext or ciphertext buffers.

public void encrypt(byte[] in, int i, byte[] out, int j, Object k, int bs)

The full encryption algorithm is given in the following four steps.INPUT: plaintext m1...m64; key K = k1...k128. OUTPUT: ciphertext c1...c64.

- (key schedule) Compute 16 pairs of subkeys {Kmi, Kri} from a user key (see makeKey() method).
- (L0,R0) <-- (m1...m64). (Split the plaintext into left and right 32-bit halves L0 = m1...m32 and R0 = m33...m64.).
- (16 rounds) for i from 1 to 16, compute Li and Ri as follows:
- Li = Ri-1;
- Ri = Li-1 ^ F(Ri-1,Kmi,Kri), where F is defined in method F() -- f is of Type 1, Type 2, or Type 3, depending on i, and ^ being the bitwise XOR function.
- c1...c64 <-- (R16,L16). (Exchange final blocks L16, R16 and concatenate to form the ciphertext.)
Decryption is identical to the encryption algorithm given above, except that the rounds (and therefore the subkey pairs) are used in reverse order to compute (L0,R0) from (R16,L16).

Looking at the iterations/rounds in pairs we have:

(1a) Li = Ri-1; (1b) Ri = Li-1 ^ Fi(Ri-1); (2a) Li+1 = Ri; (2b) Ri+1 = Li ^ Fi+1(Ri);which by substituting (2a) in (2b) becomes(2c) Ri+1 = Li ^ Fi+1(Li+1);by substituting (1b) in (2a) and (1a) in (2c), we get:(3a) Li+1 = Li-1 ^ Fi(Ri-1); (3b) Ri+1 = Ri-1 ^ Fi+1(Li+1);Using only one couple of variables L and R, initialised to L0 and R0 respectively, the assignments for each pair of rounds become:(4a) L ^= Fi(R); (4b) R ^= Fi+1(L);

Specified by:- encrypt in interface gnu.javax.crypto.cipher.IBlockCipherSpi

Parameters:`in`

- contains the plain-text 64-bit block.`i`

- start index within input where data is considered.`out`

- will contain the cipher-text block.`j`

- index in out where cipher-text starts.`k`

- the session key object.`bs`

- the desired block size.

public Iterator<E> keySizes()

Returns an`Iterator`

over the supported key sizes. Each element returned by this object is an`Integer`

.

Specified by:- keySizes in interface IBlockCipher
- keySizes in interface gnu.javax.crypto.cipher.IBlockCipherSpi

Returns:- an
`Iterator`

over the supported key sizes.

public Object makeKey(byte[] uk, int bs) throws InvalidKeyException

Expands a user-supplied key material into a session key for a designatedblock size.

Specified by:- makeKey in interface gnu.javax.crypto.cipher.IBlockCipherSpi

Parameters:`bs`

- the desired block size in bytes.

Returns:- an Object encapsulating the session key.

Throws:`IllegalArgumentException`

- if the block size is invalid.`InvalidKeyException`

- if the key data is invalid.

public boolean selfTest()

Acorrectnesstest that consists of basic symmetric encryption / decryption test(s) for all supported block and key sizes, as well as one (1) variable key Known Answer Test (KAT).

Specified by:- selfTest in interface IBlockCipher
- selfTest in interface gnu.javax.crypto.cipher.IBlockCipherSpi

Overrides:- selfTest in interface BaseCipher

Returns:`true`

if the implementation passes simplecorrectnesstests. Returns`false`

otherwise.

Cast5.java --
Copyright (C) 2003, 2006 Free Software Foundation, Inc.
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