Also known as: RC4, ARC4

RC4 (also ARC4) is a stream cipher that generates a pseudo-random keystream from a secret key and XORs it with the data.¹ It provides the “Enhanced Privacy” encryption option on some DMR systems.

RC4 is a stream cipher: a key seeds a keystream that is XORed with the data — used by DMR's basic privacy.

How it works

Only holders of the correct key can reproduce the keystream and recover the plaintext. Unlike scrambling (a public sequence), RC4’s keystream is secret — so without the key the voice cannot be recovered.

Relevance to SDR

RC4 illustrates the line between reversible whitening and true encryption: GopherTrunk can descramble whitening but cannot decode encrypted voice without the key. See DMR encryption.

Sources

1. RC4 — Wikipedia, for the stream cipher and its key-derived keystream XORed with the data. ↩

See also

• Scrambling (whitening)
• Digital Mobile Radio (DMR)
• Forward error correction (FEC)

Learn it step by step

• Encryption & what you can decode