一道简单Chacha20_RC4算法CTF题目

void ChaCha20XOR(uint8_t key[32], uint32_t counter, uint8_t nonce[12], uint8_t *in, uint8_t *out, int inlen) {    int i, j;     uint32_t s[16];    uint8_t block[64];     //static void chacha20_init_state(uint32_t s[16], uint8_t key[32], uint32_t counter, uint8_t nonce[12])    chacha20_init_state(s, key, counter, nonce);     for (i = 0; i < inlen; i += 64) {        //static void chacha20_block(uint32_t in[16], uint8_t out[64], int num_rounds)        chacha20_block(s, block, 20);        s[12]++;         for (j = i; j < i + 64; j++) {            if (j >= inlen) {                break;            }            out[j] = in[j] ^ block[j - i];        }    }}

void get_flag(unsigned char* mykey, int v0, int pid){    unsigned char s[256] = { 0 };    unsigned char key[12] = "Encrypted!!";     char hexData[48] = {        0xFC, 0xD4, 0x19, 0x74, 0x51, 0x67, 0xED, 0x4B, 0x9C, 0x48, 0xC6, 0x5F, 0x9B, 0x5D, 0xB4, 0xF0,        0x44, 0x02, 0xAF, 0xAC, 0x66, 0x01, 0x06, 0xA5, 0xBE, 0xBC, 0xD0, 0x77, 0x29, 0x64, 0x8D, 0x5E,        0x41, 0xD4, 0x77, 0x31, 0x40, 0xB4, 0x92, 0x22, 0xF9, 0x9F, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00    };  //flag.enc字节序列     int enc_len = strlen(hexData);    rc4_init(s, key, strlen((const char *)key));    rc4_crypt(s, (uint8_t *)hexData, enc_len);     ChaCha20XOR((uint8_t *)mykey, 1, key, (uint8_t *)hexData, strlen(hexData));     if (hexData[0] == 'f' && hexData[1] == 'l' && hexData[2] == 'a') {  //判定前三个字母是fla输出即可        printf("timestamp:%d,pid:%d ", v0, pid);        for (int i = 0; i < 48; i++){            printf("%c", hexData[i]);        }        printf("n");        exit(0);    }} int main() {    unsigned char mykey[32];    int timestamp;    DWORD Seed;     timestamp = 1662973302;  // time(0);  2022-09-12 17:01:42    for (int pid = 1; pid < 9000; pid++){        for (timestamp = 1662909722; timestamp <= 1662973302; timestamp++) {   //最坑的点在这里，时间戳要从出题时间点开始算起            Seed = timestamp ^ pid;            srand(Seed);            for (int i = 0; i < 32; ++i)                mykey[i] = (unsigned __int16)rand() >> 8;             get_flag(mykey, timestamp, pid);  //传入timestamp和pid纯属好奇        }    }     printf("endn");    return 0;}