// gcc -o otp_prngcrack otp_prngcrack.c -Wall -std=c99
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

int main( int argc, char *argv[] )
{
    if( argc != 4 )
    {
        printf("Usage: %s ciphertext beginTime endTime\n", argv[0] );
        return 1;
    }

    if( strlen( argv[1] ) % 2 != 0 )
    {
        printf( "Ciphertext has invalid length\n" );
        return 1;
    }

    const int length = strlen( argv[1] ) / 2;
    char decoded[length];
    for( int i = 0; i < length; i++ )
    {
        unsigned int byte;
        if( sscanf( argv[1] + 2 * i, "%02x", &byte ) != 1 )
        {
            printf( "Error parsing ciphertext\n" );
            return 1;
        }
        decoded[i] = byte & 0xff;
    }

    unsigned int beginTime, endTime;
    if( sscanf( argv[2], "%d", &beginTime ) != 1 )
    {
        printf( "Error parsing begin time\n" );
        return 1;
    }
    if( sscanf( argv[3], "%d", &endTime ) != 1 )
    {
        printf( "Error parsing end time\n" );
        return 1;
    }
    if( beginTime > endTime )
    {
        printf( "Begin time must not be greater than end time\n" );
        return 1;
    }

    for( unsigned int i = beginTime; i <= endTime; i++ )
    {
        int valid = 1;
        char decrypted[length + 1];
        decrypted[length] = '\0';
        srand( i );
        for( int j = 0; j < length; j++ )
        {
            char c = decoded[j] ^ ( rand() & 0xff );
            if( !isprint( c ) )
            {
                valid = 0;
                break;
            }
            decrypted[j] = c;
        }
        if( valid )
            printf( "[%d]: %s\n", i, decrypted );
    }

    return 0;
}