Documentation
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Overview ¶
Package keystream implements keystream-reuse / many-time-pad analysis — the real-world break against additive stream ciphers (P25 DES-OFB and ADP/RC4, TETRA AIE) when a transmitter reuses an initialisation vector. Under OFB and raw stream ciphers the keystream is a deterministic function of (key, IV); two frames sent under the same key and the same IV therefore share an identical keystream, and XORing their ciphertexts cancels it:
c1 ^ c2 = (p1 ^ ks) ^ (p2 ^ ks) = p1 ^ p2
leaving a classic running-key system that crib-dragging and a language model can peel apart — no key recovery required. For P25 the IV is the 72-bit Message Indicator the decoder already extracts, so this is the bridge from "encrypted, opaque" to "recoverable" whenever a radio's MI repeats.
This package only exploits operator misuse (IV reuse) and known plaintext; it does not attack the cipher's key, in keeping with the toolkit's scope.
Index ¶
Constants ¶
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Variables ¶
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Functions ¶
Types ¶
type Decoded ¶
Decoded is one frame recovered by RecoverWithKnown.
func RecoverWithKnown ¶
func RecoverWithKnown(group ReuseGroup, knownLabel string, knownPT []byte) (ks []byte, out []Decoded, ok bool)
RecoverWithKnown turns one known plaintext within a reuse group into the group's keystream (ks = knownPT ^ knownCT) and uses it to decrypt every other frame in the group. This is the decisive step once any single frame's content is known (a standard tone, a known data payload, a confirmed transcript). It returns the recovered keystream and the decrypted frames.
type DragHit ¶
type DragHit struct {
CribLabel string
PartnerLabel string
Offset int
Revealed []byte
Score float64
}
DragHit is one crib-drag placement: positioning crib at Offset in one ciphertext reveals Revealed in the partner, scored by a language model.
func CribDragGroup ¶
func CribDragGroup(group ReuseGroup, crib []byte, topN int) []DragHit
CribDragGroup slides crib across every ordered ciphertext pair in the group (c_i ^ c_j ^ crib) and returns the placements whose revealed partner bytes are fully printable, ranked by English trigram score — the highest are the likely true positions. With the right crib this peels plaintext out of a reuse group with no key and no known plaintext.
type Frame ¶
Frame is one captured encrypted unit: an IV (e.g. a P25 Message Indicator) and the ciphertext under that IV. Label identifies the source (call id, timestamp) for reporting. AlgID/KeyID are the optional algorithm and key identifiers from the capture (0 when unknown), used by the assessment harness to select the right cipher for a decryption attempt.
type ReuseGroup ¶
ReuseGroup is a set of frames that share an identical IV and therefore an identical keystream.
func FindReuse ¶
func FindReuse(frames []Frame) []ReuseGroup
FindReuse groups frames sharing an identical IV, returning only groups with at least two frames (the exploitable ones), largest group first. Frames with an empty IV are ignored — without an IV there is nothing to collide.
Source Files