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Here is a small encryption program I wrote after hearing a podcast mentioning XOR encryption. Thought it could be fun for others and maybe spark some ideas for your own projects. #include <stdio.h> #include <unistd.h> #include <stdbool.h> #include <string.h> /** * An XOR encryption tool * * Usage: xor [-k key] [file or stdin] */ static void xor_operate(const char *str, int strLen, const char *key) { static int keyIndex = 0; int keyLen = strlen(key); for (size_t i = 0; i < strLen; ++i) { char ch = str[i] ^ key[keyIndex++]; printf("%c", ch); if (keyIndex >= keyLen) keyIndex = 0; } } int main(int argc, char* argv[]) { int opt; const char *key = "defaultkey"; while ((opt = getopt(argc, argv, "k:")) != -1) { switch (opt) { case 'k': key = optarg; break; default: break; } } fprintf(stderr, "Key: %s\n", key); FILE *in = fopen(argv[optind], "r"); if (in == NULL) in = stdin; char buffer[1024]; unsigned int i = 0; char ch; while ((ch = fgetc(in)) != -1) { buffer[i++] = ch; if (i >= 1024) { xor_operate(buffer, i, key); i = 0; } } xor_operate(buffer, i, key); return 0; }