package ro.pub.cs.pp.a51hadoop.algorithm.a51;

import ro.pub.cs.pp.a51hadoop.algorithm.Hashfn;
import ro.pub.cs.pp.a51hadoop.algorithm.a51.A51Bitops;
import ro.pub.cs.pp.a51hadoop.algorithm.a51.A51Constants;


public class A51KeySetup
{
	public final int[] R;



	/*
	 * Clock all three of R1,R2,R3, ignoring their middle bits.
	 * This is only used for key setup.
	 */
	private static int[] clockallthree(final int[] R)
	{
		int ret[] = new int[R.length];
		for(int i = 0; i < R.length; i++)
			ret[i] = A51Bitops.clockone(R[i], A51Constants.R_mask[i],
						    A51Constants.R_feedback_taps[i]);
		return ret;
	}


	/* Do the A5/1 key setup.  This routine accepts a 64-bit key
	 * and a 22-bit frame number. */
	public static int[] keysetup(int[] key, int frame)
	{
		int i;
		int[] R = new int[3];
		
		/* Zero out the shift registers. */
		for(i = 0; i < R.length; i++)
			R[i] = 0;

		/* Load the key into the shift registers, LSB of first
		 * byte of key array first, clocking each register
		 * once for every key bit loaded.  (The usual clock
		 * control rule is temporarily disabled.) */
		for (i = 0; i < 64; i++)
		{
			R = clockallthree(R); /* always clock */
			int keybit = (key[i/8] >> (i & 7)) & 1; /* The i-th bit of the key */
			for(int j = 0; j < R.length; j++)
				R[j] ^= keybit;
		}

		/* Load the frame number into the shift
		 * registers, LSB first,
		 * clocking each register once for every
		 * key bit loaded.  (The usual clock
		 * control rule is still disabled.) */
		for (i = 0; i < 22; i++)
		{
			R = clockallthree(R); /* always clock */
			int framebit = (frame >> i) & 1; /* The i-th bit of the frame # */
			for(int j = 0; j < R.length; j++)
				R[j] ^= framebit;
		}

		/* Run the shift registers for 100 clocks
		 * to mix the keying material and frame number
		 * together with output generation disabled,
		 * so that there is sufficient avalanche.
		 * We re-enable the majority-based clock control
		 * rule from now on. */
		for (i=0; i<100; i++)
		{
			R = A51Hashfn.clock(R);
		}
		
		/* Now the key is properly set up. */
		return R;
	}

	public A51KeySetup(int[] key, int frame)
	{
		this.R = keysetup(key, frame);
	}
}