moth/packages/mcp/src/arc4.c

231 lines
4.5 KiB
C

#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include "arc4.h"
#define swap(a, b) do {uint8_t _swap=a; a=b, b=_swap;} while (0)
void
arc4_init(struct arc4_ctx *ctx, uint8_t const *key, size_t keylen)
{
int i;
int j = 0;
for (i = 0; i < 256; i += 1) {
ctx->S[i] = i;
}
for (i = 0; i < 256; i += 1) {
j = (j + ctx->S[i] + key[i % keylen]) % 256;
swap(ctx->S[i], ctx->S[j]);
}
ctx->i = 0;
ctx->j = 0;
}
uint8_t
arc4_out(struct arc4_ctx *ctx)
{
ctx->i = (ctx->i + 1) % 256;
ctx->j = (ctx->j + ctx->S[ctx->i]) % 256;
swap(ctx->S[ctx->i], ctx->S[ctx->j]);
return ctx->S[(ctx->S[ctx->i] + ctx->S[ctx->j]) % 256];
}
void
arc4_crypt(struct arc4_ctx *ctx,
uint8_t *obuf, const uint8_t *ibuf, size_t buflen)
{
size_t k;
for (k = 0; k < buflen; k += 1) {
obuf[k] = ibuf[k] ^ arc4_out(ctx);
}
}
/* Create a nonce as an arc4 stream with key=seed */
void
arc4_nonce(uint8_t *nonce, size_t noncelen,
void *seed, size_t seedlen)
{
struct arc4_ctx ctx;
int i;
arc4_init(&ctx, seed, seedlen);
for (i = 0; i < noncelen; i += 1) {
nonce[i] = arc4_out(&ctx);
}
}
/***************************************************
*
* Psuedo Random Number Generation
*
*/
static struct arc4_ctx prng_ctx;
static int prng_initialized = 0;
void
arc4_rand_seed(const uint8_t *seed, size_t seedlen)
{
arc4_init(&prng_ctx, seed, seedlen);
prng_initialized = 1;
}
static void
arc4_rand_autoseed()
{
if (! prng_initialized) {
uint8_t key[ARC4_KEYLEN];
FILE *urandom;
/* Open /dev/urandom or die trying */
urandom = fopen("/dev/urandom", "r");
if (! urandom) {
perror("Opening /dev/urandom");
abort();
}
setbuf(urandom, NULL);
fread(&key, sizeof(key), 1, urandom);
fclose(urandom);
arc4_rand_seed(key, sizeof(key));
}
}
uint8_t
arc4_rand8()
{
arc4_rand_autoseed();
return arc4_out(&prng_ctx);
}
uint32_t
arc4_rand32()
{
arc4_rand_autoseed();
return ((arc4_out(&prng_ctx) << 0) |
(arc4_out(&prng_ctx) << 8) |
(arc4_out(&prng_ctx) << 16) |
(arc4_out(&prng_ctx) << 24));
}
/*****************************************
*
* Stream operations
*
*/
ssize_t
arc4_encrypt_stream(FILE *out, FILE *in,
const uint8_t *key, size_t keylen)
{
struct arc4_ctx ctx;
uint32_t seed = arc4_rand32();
uint8_t nonce[ARC4_KEYLEN];
ssize_t written = 0;
int i;
fwrite("arc4", 4, 1, out);
fwrite(&seed, sizeof(seed), 1, out);
arc4_nonce(nonce, sizeof(nonce), &seed, sizeof(seed));
for (i = 0; i < keylen; i += 1) {
nonce[i] ^= key[i];
}
arc4_init(&ctx, nonce, sizeof(nonce));
while (1) {
int c = fgetc(in);
if (EOF == c) break;
fputc((uint8_t)c ^ arc4_out(&ctx), out);
written += 1;
}
return written;
}
ssize_t
arc4_decrypt_stream(FILE *out, FILE *in,
const uint8_t *key, size_t keylen)
{
struct arc4_ctx ctx;
uint32_t seed;
uint8_t nonce[ARC4_KEYLEN];
ssize_t written = 0;
char sig[4];
int i;
fread(&sig, sizeof(sig), 1, in);
if (memcmp(sig, "arc4", 4)) {
return -1;
}
fread(&seed, sizeof(seed), 1, in);
arc4_nonce(nonce, sizeof(nonce), &seed, sizeof(seed));
for (i = 0; i < keylen; i += 1) {
nonce[i] ^= key[i];
}
arc4_init(&ctx, nonce, sizeof(nonce));
while (1) {
int c = fgetc(in);
if (EOF == c) break;
fputc((uint8_t)c ^ arc4_out(&ctx), out);
written += 1;
}
return written;
}
#ifdef ARC4_MAIN
#include <sysexits.h>
#include <unistd.h>
int
main(int argc, char *argv[])
{
uint8_t key[ARC4_KEYLEN] = {0};
size_t keylen;
/* Read key and initialize context */
{
char *ekey = getenv("KEY");
if (ekey) {
keylen = strlen(ekey);
memcpy(key, ekey, keylen);
} else {
keylen = read(3, key, sizeof(key));
if (-1 == keylen) {
fprintf(stderr, "error: must specify key.\n");
return 1;
}
}
}
if (! argv[1]) {
if (-1 == arc4_decrypt_stream(stdout, stdin, key, keylen)) {
fprintf(stderr, "error: not an arc4 stream.\n");
return 1;
}
} else if (0 == strcmp(argv[1], "-e")) {
arc4_encrypt_stream(stdout, stdin, key, keylen);
} else {
fprintf(stderr, "Usage: %s [-e] <PLAINTEXT\n", argv[0]);
fprintf(stderr, "\n");
fprintf(stderr, "You must pass in a key on fd 3 or in the environment variable KEY.\n");
return EX_USAGE;
}
return 0;
}
#endif /* ARC4_MAIN */