cbccipher.java

JAVA的加密源程序

/*
Christoforos Pirillos @ Villanova University - May 1999
based on code from the book "Java Network Programming" by Hughes
*/

package encryption;
/**

/**The CBCCipher class is a Cipher that attaches to an existing
block-cipher and applies CBC stream-encryption to it.*/

public class CBCCipher extends Cipher {

/**The Cipher used for encryption*/
protected Cipher c;

protected byte[] oldEncipher, oldDecipher;

/**The block size of the cipher used*/
protected int bS;

/**Accepts a Cipher to be used and an initialization vector that will be
used to initialize the cipher-block-chaining*/

public CBCCipher (Cipher c, byte[] iv) {
	this.c=c;
	bS=c.blockSize();
	oldEncipher=new byte[bS];
	oldDecipher=new byte[bS];
	if (iv!= null) {
		System.arraycopy (iv,0,oldEncipher,0,bS);
		System.arraycopy (iv,0,oldDecipher,0,bS);
	}
}

/**same as CBCCipher (Cipher, byte[]) but assumes byte[]=0*/

public CBCCipher (Cipher c) {
	this (c,null);
}

/**Encrypts a block using X-OR on the plaintext with the previous
ciphertext block and then encrypt this with the Cipher*/

public void encipherBlock (byte[] plain, int po, byte[] cipher, int co) {
	for (int i=0;i<bS;++i)
		cipher[co+i]=(byte)(oldEncipher[i]^plain[po+i]);
	c.encipherBlock(cipher,co,cipher,co);
	System.arraycopy (cipher, co, oldEncipher, 0, bS);
}

/**The reverse procedure of encipherBlock method */

public void decipherBlock (byte[] cipher, int co, byte[] plain, int po) {
	c.decipherBlock (cipher, co, plain, po);
	for (int i=0;i<bS;++i) {
		byte o = cipher[co+i];
		plain[po+i] ^= oldDecipher[i];
		oldDecipher[i]=o;
	}
}

/**Returns the block size of the Cipher being used*/
public int blockSize() {
	return bS;
}


}