randomseed.c

//
//  main.c
//  randomseed
//
//  Created by Harlan Haskins on 1/10/16.
//  Copyright © 2016 Harlan. All rights reserved.
//

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

void testseed(uint32_t seed, size_t len, char *res) {
    srand(seed);
    for (size_t i = 0; i < len; i++) {
        res[i] = (char)rand();
    }
}

int main(int argc, const char * argv[]) {
    if (argc < 2) {
        puts("Usage: randomseed [string]");
        return EXIT_FAILURE;
    }
    size_t len = strlen(argv[1]);
    char *res = calloc(sizeof(char), len);
    int found = 0;
    uint32_t seed = 0;
    while (seed < UINT32_MAX) {
        testseed(seed, len, res);
//        printf("[%u]: %s\n", seed, res);
        if (strncmp(res, argv[1], len) == 0) {
            found = 1;
            break;
        }
        seed++;
    }
    if (found) {
        printf("Seed found! %u\n", seed);
        printf("Res: %s, String: %s\n", res, argv[1]);
    } else {
        printf("No seed found for %s", argv[1]);
    }
    free(res);
    return 0;
}

Will find a seed for the libc random number generator that generates whatever string you give it.