41 lines
1.1 KiB
C
41 lines
1.1 KiB
C
//-----------------------------------------------------------------------------
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// This code is licensed to you under the terms of the GNU GPL, version 2 or,
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// at your option, any later version. See the LICENSE.txt file for the text of
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// the license.
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//-----------------------------------------------------------------------------
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// LEFIC's obfuscation function
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//-----------------------------------------------------------------------------
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#include "legic_prng.h"
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struct lfsr {
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uint8_t a;
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uint8_t b;
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uint32_t c;
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} lfsr;
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void legic_prng_init(uint8_t init) {
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lfsr.a = init;
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lfsr.b = 0; // hack to get a always 0 keystream
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lfsr.c = 0;
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if(init)
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lfsr.b = (init << 1) | 1;
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}
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void legic_prng_forward(int count) {
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lfsr.c += count;
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while(count--) {
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// According: http://www.proxmark.org/forum/viewtopic.php?pid=5437#p5437
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lfsr.a = (lfsr.a >> 1 | (lfsr.a ^ lfsr.a >> 6) << 6) & 0x7F;
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lfsr.b = lfsr.b >> 1 | (lfsr.b ^ lfsr.b >> 2 ^ lfsr.b >> 3 ^ lfsr.b >> 7) << 7;
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}
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}
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uint32_t legic_prng_count() {
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return lfsr.c;
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}
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uint8_t legic_prng_get_bit() {
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uint8_t idx = 7 - ( (lfsr.a & 4) | (lfsr.a >> 2 & 2) | (lfsr.a >> 4 & 1) );
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return lfsr.b >> idx & 1;
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} |