source: proiecte/HadoopA51/src/java/ro/pub/cs/pp/a51hadoop/algorithm/a51/A51KeySetup.java @ 166

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);
        }
}