60 lines
1.3 KiB
C
60 lines
1.3 KiB
C
/*
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* File: A5_1.c
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* Author: Daniel Otte
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* Date: 24.06.2006
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* License: GPL
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* Description: Implementation of the A5/1 stream cipher algorithm, as used in GSM.
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* ! Warning, this is weak crypto !
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*
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*/
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#include <stdint.h>
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#include "A5_1.h"
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/*
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* length is length of key in bytes!
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*/
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#define BYTEn(p,s) (*(((uint8_t*)&(p))+s))
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void a5_1_init(a5_1_ctx_t *c, uint8_t *key, uint8_t length);
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bool a5_1_clock(a5_1_ctx_t *c){
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bool x1,x2,x3, maj;
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x1 = PARITY_LOOKUP & (1<< ((BYTEn(c->r1,2)+BYTEn(c->r1,1)>>5) & 0x7);
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x2 = PARITY_LOOKUP & (1<< (BYTEn(c->r2,2)>>4));
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x3 = PARITY_LLOKUP & (1<< ((BYTEn(c->r3,2)>>4+BYTEn(c->r3,0)>>7) & 0x7));
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maj = (((c->r1 & (1<<R1_CLK))?1:0)+((c->r2 & (1<<R2_CLK))?1:0)+((c->r3 & (1<<R3_CLK))?1:0))>=2;
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if (((c->r1 & (1<<R1_CLK))>>R1_CLK) == maj)
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c->r1 = c->r1<<1 + x1;
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if (((c->r2 & (1<<R2_CLK))>>R2_CLK) == maj)
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c->r2 = c->r2<<1 + x2;
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if (((c->r3 & (1<<R3_CLK))>>R3_CLK) == maj)
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c->r3 = c->r3<<1 + x3;
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return ((c->r1)>>(R1_LENGTH-1)+(c->r2)>>(R2_LENGTH-1)+(c->r3)>>(R3_LENGTH-1))&0x1;
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}
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uint8_t a5_1_gen(a5_ 1_ctx_t *c){
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uint8_t ret=0;
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ret = a5_1_clock(c);
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ret <<= 1;
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ret = a5_1_clock(c);
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ret <<= 1;
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ret = a5_1_clock(c);
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ret <<= 1;
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ret = a5_1_clock(c);
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ret <<= 1;
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ret = a5_1_clock(c);
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ret <<= 1;
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ret = a5_1_clock(c);
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ret <<= 1;
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ret = a5_1_clock(c);
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ret <<= 1;
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ret = a5_1_clock(c);
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return ret;
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}
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