Skip to main content

RC4 Cipher (rc4)

RC4 symmetric stream cipher, encrypts/decrypts data in-place. Encryption and decryption use the same operation: applying the same key a second time restores the original plaintext.

API​

void rc4_crypt(uint8_t * key, int kl, uint8_t * dat, int dl);
  • key — Key buffer
  • kl — Key length in bytes
  • dat — Data buffer (modified in-place)
  • dl — Data length in bytes

Data is modified in-place. RC4 is symmetric, so calling rc4_crypt with the same key a second time decrypts the data.

Example​

Encrypt and Decrypt​

uint8_t key[] = { 'x', 'b', 'o', 'o', 't' };
uint8_t data[] = { 'h', 'e', 'l', 'l', 'o' };

rc4_crypt(key, sizeof(key), data, sizeof(data));
/* data is now encrypted */

rc4_crypt(key, sizeof(key), data, sizeof(data));
/* data is restored to plaintext */

Encrypt→Decrypt Round-Trip Verification​

uint8_t key[] = { 'x', 'b', 'o', 'o', 't' };
uint8_t dat[256];
uint8_t tmp[256];

xos_memcpy(tmp, dat, sizeof(dat));
rc4_crypt(key, 5, tmp, sizeof(tmp));
rc4_crypt(key, 5, tmp, sizeof(tmp));
/* memcmp(dat, tmp, sizeof(dat)) == 0 */