mode-ctr-gladman.js

/** @preserve
 * Counter block mode compatible with  Dr Brian Gladman fileenc.c
 * derived from CryptoJS.mode.CTR 
 * Jan Hruby jhruby.web@gmail.com
 */
CryptoJS.mode.CTRGladman = (function () {
    var CTRGladman = CryptoJS.lib.BlockCipherMode.extend();

	function incWord(word)
	{	
		if (((word >> 24) & 0xff) === 0xff) { //overflow
		var b1 = (word >> 16)&0xff;
		var b2 = (word >> 8)&0xff;
		var b3 = word & 0xff;

		if (b1 === 0xff) // overflow b1
		{		 
		b1 = 0;
		if (b2 === 0xff)
		{
			b2 = 0;
			if (b3 === 0xff)
			{
				b3 = 0;
			}
			else
			{
				++b3;
			}
		}
		else
		{
			++b2;
		}
		}
		else
		{
		++b1;
		}

		word = 0;	  	  
		word += (b1 << 16);
		word += (b2 << 8);
		word += b3;	  
		}
		else
		{
		word += (0x01 << 24);
		}
		return word;
	}

	function incCounter(counter)
	{
		if ((counter[0] = incWord(counter[0])) === 0)
		{
			// encr_data in fileenc.c from  Dr Brian Gladman's counts only with DWORD j < 8
			counter[1] = incWord(counter[1]);
		}
		return counter;
	}
	
    var Encryptor = CTRGladman.Encryptor = CTRGladman.extend({
        processBlock: function (words, offset) {
            // Shortcuts
            var cipher = this._cipher
            var blockSize = cipher.blockSize;
            var iv = this._iv;
            var counter = this._counter;

            // Generate keystream
            if (iv) {
                counter = this._counter = iv.slice(0);

                // Remove IV for subsequent blocks
                this._iv = undefined;
            }
            
			incCounter(counter);
			
			var keystream = counter.slice(0);
            cipher.encryptBlock(keystream, 0);

            // Encrypt
            for (var i = 0; i < blockSize; i++) {
                words[offset + i] ^= keystream[i];
            }
        }
    });

    CTRGladman.Decryptor = Encryptor;

    return CTRGladman;
}());