122 lines
2.5 KiB
C
122 lines
2.5 KiB
C
/**
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*
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* author: Daniel Otte
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* email: daniel.otte@rub.de
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* license: GPLv3
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*
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*/
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#include <stdint.h>
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#include <string.h>
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#include <avr/pgmspace.h>
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#include "grain.h"
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#define GRAIN_REVERSEKEY
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/* s0, s1, s2, ..., s78, s79 */
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#define S(i) ((ctx->lfsr[9-((i)/8)])>>(7-((i)%8)))
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/* b0, b1, b2, ..., b78, b79 */
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#define B(i) ((ctx->nfsr[9-((i)/8)])>>(7-((i)%8)))
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uint8_t h_lut[4] PROGMEM = {0x4C, 0xB6, 0xD3, 0x26};
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uint8_t grain_enc(grain_ctx_t* ctx){
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uint8_t s80, s0, c1, c2;
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uint8_t i;
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/* clock the LFSR */
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s0=S(0);
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s80 =S(62) ^ S(51) ^ S(38) ^ S(23) ^ S(13) ^ s0;
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s80 &= 1;
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c1 = s80;
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for(i=0; i<10; ++i){
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c2 = (ctx->lfsr[i])>>7;
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ctx->lfsr[i] = ((ctx->lfsr[i])<<1) | c1;
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c1 = c2;
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}
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/* clock the NFSR */
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uint8_t b80, a,b,d,e;
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b80 = B(62) ^ B(60) ^ B(52) ^ B(45) ^
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B(37) ^ B(33) ^ B(28) ^ B(21) ^
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B(14) ^ B( 9) ^ B( 0) ^ s0;
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b80 ^= (a = B(63) & B(60));
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b80 ^= (b = B(37) & B(33));
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b80 ^= B(15) & B( 9); /* c */
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b80 ^= (d = B(60) & B(52) & B(45));
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b80 ^= (e = B(33) & B(28) & B(21));
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b80 ^= B(63) & B(45) & B(28) & B(9); /* f */
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/* -- */
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b80 ^= b & B(60) & B(52); /* g */
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b80 ^= a & B(21) & B(15); /* h */
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b80 ^= d & B(63) & B(37); /* i */
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b80 ^= e & B(15) & B( 9); /* j */
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b80 ^= e & B(52) & B(45) & B(37); /* k */
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c1 = b80 & 1;
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for(i=0; i<10; ++i){
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c2 = (ctx->nfsr[i])>>7;
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ctx->nfsr[i] = ((ctx->nfsr[i])<<1) | c1;
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c1 = c2;
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}
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/* now the h function */
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uint8_t h;
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i = (S(2)&1) |
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((S(24)&1) << 1) |
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((S(45)&1) << 2) |
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((S(63)&1) << 3) |
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((B(62)&1) << 4);
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h = (pgm_read_byte(h_lut+(i/8)))>>(i%8);
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h ^= B(0) ^ B(1) ^ B(3) ^ B(9) ^ B(30) ^ B(42) ^ B(55);
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return h&1;
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}
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#ifdef GRAIN_REVERSEKEY
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static
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uint8_t reverse_bits(uint8_t a){
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uint8_t lut[16] = {
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0x0, 0x8, 0x4, 0xC, /* 0000 1000 0100 1100 */
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0x2, 0xA, 0x6, 0xE, /* 0010 1010 0110 1110 */
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0x1, 0x9, 0x5, 0xD, /* 0001 1001 0101 1101 */
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0x3, 0xB, 0x7, 0xF }; /* 0011 1011 0111 1111 */
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uint8_t x;
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x = ((lut[a&0xf]) << 4) | lut[a>>4];
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return x;
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}
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#else
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#define reverse_bits(a) (a)
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#endif
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void grain_init(const void* key, const void* iv, grain_ctx_t* ctx){
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uint8_t i,t;
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/* load the 80bit key */
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for(i=0; i<10; ++i){
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ctx->nfsr[9-i] = reverse_bits(((uint8_t*)key)[i]);
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}
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/* load the 64bit iv */
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for(i=0; i<8; ++i){
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ctx->lfsr[9-i] = reverse_bits(((uint8_t*)iv)[i]);
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}
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/* set the other bits of iv to 1 */
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ctx->lfsr[0] = ctx->lfsr[1] = 0xFF;
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/* run it 160 times */
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for(i=0; i<160; ++i){
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t = grain_enc(ctx);
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(ctx->lfsr[0]) ^= t;
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(ctx->nfsr[0]) ^= t;
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}
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}
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