Documentation
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Overview ¶
Package rc4 implements the RC4 stream cipher (also known as ARC4, "alleged RC4") as a keystream generator.
GopherTrunk uses it to decode DMR voice traffic protected by ARC4-based "Enhanced Privacy" when the operator already holds the key. The Go standard library's crypto/rc4 is deprecated — it raises staticcheck SA1019 at every call site, which `make lint` rejects — so this small, dependency-free implementation is vendored in its place. It is pinned against the canonical RC4 test vectors in rc4_test.go so codebook drift stays detectable.
RC4 is cryptographically broken and must never be used to PROTECT data. It exists here only to DECODE third-party transmissions whose key the operator is authorized to hold — the same known-key model SDRTrunk, DSD-FME and OP25 use. No key recovery is performed.
Index ¶
Constants ¶
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Variables ¶
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Functions ¶
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Types ¶
type Cipher ¶
type Cipher struct {
// contains filtered or unexported fields
}
Cipher is an RC4 keystream generator. A Cipher is stateful: every call to XORKeyStream or KeyStream advances the internal PRGA state, so one Cipher yields a single continuous keystream. A Cipher is not safe for concurrent use; construct one per call chain.
func NewCipher ¶
NewCipher returns a Cipher keyed with key, which must be 1..256 bytes. The key-scheduling algorithm (KSA) runs here; the returned Cipher is positioned at the first keystream byte.
func (*Cipher) KeyStream ¶
KeyStream returns the next n bytes of raw keystream and advances the Cipher by n bytes. It is equivalent to XORKeyStream against n zero bytes — convenient when the caller wants the keystream itself, for example to XOR onto a bit-unpacked voice frame.
func (*Cipher) XORKeyStream ¶
XORKeyStream XORs each byte of src with the next keystream byte and writes the result to dst, advancing the keystream by len(src). dst must be at least len(src) long; dst and src may be the same slice.
Source Files