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基于LFSR的流密钥生成器

利用2个LFSR，输出30位流密码

#include <stdio.h>#include<stdlib.h>/*两个寄存器的位数 */#define R1MASK  0x1F /* 5 bits, numbered 0..4 */#define R2MASK  0x0F /* 4 bits, numbered 0..3 *//* 每个寄存器的中间比特 */#define R1MID   0x02 /* bit 2 */#define R2MID   0x02 /* bit 2 *//* 回归标志，用于钟控轮转寄存器*/ /* 特征多项式*/ /*f(x)=x^5+x^4+1;f(x)=x^4+x^3+1. */#define R1TAPS  0x18 /* bits 4,3 */#define R2TAPS  0x0C /* bits 3,2 */ /* 输出标记，用于生成输出 */#define R1OUT   0x10 /* bit 4 (the high bit) */#define R2OUT   0x08 /* bit 3 (the high bit) */typedef unsigned char byte;typedef unsigned int word;typedef word bit;/* 计算移位后填入值 */bit parity(word x) {    x ^= x >> 8;    x ^= x >> 4;    x ^= x >> 2;    x ^= x >> 1;    return x & 1;}/* 钟控单个寄存器 */word clockone(word reg, word mask, word taps) {    word t = reg & taps;    reg = (reg << 1) & mask;    reg |= parity(t);    return reg;}/* 两个钟控寄存器 */word R1, R2;byte m[8] = { 0X01,0x02,0x04,0x08,0x10,0x20,0x40,0x80 };/* 根据钟控规则进行钟控*/void clock() {    bit maj = (((R1 & R1MID) >> 1)* ((R2 & R2MID) >> 1)) << 1;    if ((R1 & R1MID)  == maj)        R1 = clockone(R1, R1MASK, R1TAPS);    if ((R2 & R2MID) == maj)        R2 = clockone(R2, R2MASK, R2TAPS);}/* 对两个都进行钟控，当且仅当用于设置密钥 */void clockallthree() {    R1 = clockone(R1, R1MASK, R1TAPS);    R2 = clockone(R2, R2MASK, R2TAPS);}/* 生成输出值 */bit getbit() {    return parity(R1 & R1OUT) ^ parity(R2 & R2OUT);}/* 进行A5/1密钥设置，这步骤需要64bit密钥和22bit帧数*/void keysetup(byte key[2], word frame) {    int i;    bit keybit, framebit;    /*对移位寄存器置零. */    R1 = R2 = 0;    /* 将密钥加载入寄存器,     * 优先将每个密钥串的第一个bit作为最低有效位,     *对于每个载入的密钥钟控每个寄存器一次 */    for (i = 0; i < 16; i++) {        clockallthree(); /* always clock */        keybit = (key[i / 8] >> (i & 7)) & 1; /* The i-th bit of thekey */        R1 ^= keybit; R2 ^= keybit;    }    /* 将帧数载入移位寄存器，优先最低有效位,    对每个载入的bit钟控寄存器一次 */    for (i = 0; i < 4; i++) {        clockallthree(); /* always clock */        framebit = (frame >> i) & 1; /* The i-th bit of the frame #*/        R1 ^= framebit; R2 ^= framebit;;    }    /*进行不产生输出的20次钟控来融合密钥要素与帧数     */    for (i = 0; i < 20; i++) {        clock();    }    /* 现在密钥已经完全设置完成. */}/* 生成30bit的密钥流输出*/void run(byte S[]) {    int i;    /* 将输出缓存置零. */    for (i = 0; i <= 30 / 8; i++)        S[i] = 0;    /* 生成30bit密钥流用于*/    for (i = 0; i < 30; i++) {        clock();        S[i / 8] |= getbit() << (7 - (i & 7));    }}void EnCrypt(byte *p,byte * s,int len){    int i = 0, j = 0;    while (p[i] != '\0')    {        j = i * 8 % len; //该块开头对应的密钥bit位        for (int k = j; k < j + 8; k++)        {            p[i] ^= s[k % (len / 8 + 1)] ^ m[(k % len) % 8];        }        i++;    }}void test() {    byte key[2] = { 0x01, 0x9C };    word frame = 0x34;    byte S[4] = {0};    int i, failed = 0,j;    keysetup(key, frame);    run(S);    printf("密钥为: 0x");    for (i = 0; i < 2; i++)        printf("%02X", key[i]);    printf("\n");    printf("frame number: 0x%06X\n", (unsigned int)frame);    printf("\n");    printf("observed output:\n");    printf(" 密钥流为: 0x");    for (i = 0; i < 4; i++)        printf("%02X", S[i]);    printf("\n\n\n");    byte p[7] = "朱靖宇";    i = j = 0;    printf("明文为 :%s\n", p);    while (p[i] != '\0')    {        printf("%0x ", p[i++]);    }    printf("\n\n");    i = 0;    printf(">>>>开始加密<<<<\n");    EnCrypt(p, S, 30);    printf("密文为: 0X");    while (p[i] != '\0')    {        printf(" %02X", p[i]);        i++;    }    printf("\n\n\n");    i = 0;    printf(">>>>开始解密<<<<\n");    EnCrypt(p, S, 30);    printf("明文为: ");    while (p[i] != '\0')    {        if (i % 2)            printf("%c%c", p[i - 1], p[i]);        i++;    }    printf("\n");}int main(void) {    test();    return 0;}