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             #include <fstream>
#include <chrono>
#include <cstring>

char base16[] = "0123456789ABCDEF";

struct Secret {
    unsigned char bytes[16];

    char* encode() {
        static char s[33];
        for (int i = 0; i < 16; i++) {
            s[i*2] = base16[(bytes[i] >> 4) & 15];
            s[i*2+1] = base16[bytes[i] & 15];
        }
        s[32] = '\0';
        return s;
    }

    void decode(char* s){
        for(int i = 0; i < 16; i++) {
            bytes[i] = ((strchr(base16, s[i*2]) - base16) << 4)
                    | (strchr(base16, s[i*2+1]) - base16);
        }
    }

    void generate() {
        std::srand(std::chrono::high_resolution_clock::now().time_since_epoch().count());
        int r, i, j;
        for (i = 0; i < 16; i += 4) {
            r = std::rand();
            for (j = 0; j < 4; j++) {
                bytes[i + j] = r & 255;
                r >>= 8;
            }
        }
    }
};

struct otp {

};

int main() {
    Secret secret;

    secret.generate();
    for (int i = 0; i < 16; i++) {
        printf("%u ", secret.bytes[i]);
    }
    char* s = secret.encode();
    printf("\n%s\n", s);
    secret.decode(s);
    for (int i = 0; i < 16; i++) {
        printf("%u ", secret.bytes[i]);
    }
    s = secret.encode();
    printf("\n%s\n", s);

    return 0;
}