[166] | 1 | package ro.pub.cs.pp.a51hadoop.algorithm.a51; |
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| 2 | |
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| 3 | import ro.pub.cs.pp.a51hadoop.algorithm.Hashfn; |
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| 4 | import ro.pub.cs.pp.a51hadoop.algorithm.a51.A51Bitops; |
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| 5 | import ro.pub.cs.pp.a51hadoop.algorithm.a51.A51Constants; |
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| 6 | |
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| 7 | |
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| 8 | public class A51KeySetup |
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| 9 | { |
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| 10 | public final int[] R; |
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| 11 | |
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| 12 | |
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| 13 | |
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| 14 | /* |
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| 15 | * Clock all three of R1,R2,R3, ignoring their middle bits. |
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| 16 | * This is only used for key setup. |
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| 17 | */ |
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| 18 | private static int[] clockallthree(final int[] R) |
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| 19 | { |
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| 20 | int ret[] = new int[R.length]; |
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| 21 | for(int i = 0; i < R.length; i++) |
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| 22 | ret[i] = A51Bitops.clockone(R[i], A51Constants.R_mask[i], |
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| 23 | A51Constants.R_feedback_taps[i]); |
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| 24 | return ret; |
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| 25 | } |
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| 26 | |
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| 27 | |
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| 28 | /* Do the A5/1 key setup. This routine accepts a 64-bit key |
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| 29 | * and a 22-bit frame number. */ |
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| 30 | public static int[] keysetup(int[] key, int frame) |
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| 31 | { |
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| 32 | int i; |
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| 33 | int[] R = new int[3]; |
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| 34 | |
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| 35 | /* Zero out the shift registers. */ |
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| 36 | for(i = 0; i < R.length; i++) |
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| 37 | R[i] = 0; |
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| 38 | |
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| 39 | /* Load the key into the shift registers, LSB of first |
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| 40 | * byte of key array first, clocking each register |
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| 41 | * once for every key bit loaded. (The usual clock |
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| 42 | * control rule is temporarily disabled.) */ |
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| 43 | for (i = 0; i < 64; i++) |
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| 44 | { |
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| 45 | R = clockallthree(R); /* always clock */ |
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| 46 | int keybit = (key[i/8] >> (i & 7)) & 1; /* The i-th bit of the key */ |
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| 47 | for(int j = 0; j < R.length; j++) |
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| 48 | R[j] ^= keybit; |
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| 49 | } |
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| 50 | |
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| 51 | /* Load the frame number into the shift |
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| 52 | * registers, LSB first, |
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| 53 | * clocking each register once for every |
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| 54 | * key bit loaded. (The usual clock |
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| 55 | * control rule is still disabled.) */ |
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| 56 | for (i = 0; i < 22; i++) |
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| 57 | { |
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| 58 | R = clockallthree(R); /* always clock */ |
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| 59 | int framebit = (frame >> i) & 1; /* The i-th bit of the frame # */ |
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| 60 | for(int j = 0; j < R.length; j++) |
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| 61 | R[j] ^= framebit; |
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| 62 | } |
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| 63 | |
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| 64 | /* Run the shift registers for 100 clocks |
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| 65 | * to mix the keying material and frame number |
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| 66 | * together with output generation disabled, |
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| 67 | * so that there is sufficient avalanche. |
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| 68 | * We re-enable the majority-based clock control |
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| 69 | * rule from now on. */ |
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| 70 | for (i=0; i<100; i++) |
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| 71 | { |
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| 72 | R = A51Hashfn.clock(R); |
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| 73 | } |
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| 74 | |
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| 75 | /* Now the key is properly set up. */ |
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| 76 | return R; |
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| 77 | } |
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| 78 | |
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| 79 | public A51KeySetup(int[] key, int frame) |
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| 80 | { |
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| 81 | this.R = keysetup(key, frame); |
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| 82 | } |
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| 83 | } |
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| 84 | |
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