dvb-csa

Pure-Rust implementation of the DVB Common Scrambling Algorithm (CSA2) — the cipher underneath conditional access on DVB-S, DVB-T, and DVB-C.

Status: oracle-validated, not spec-cited

DVB-CSA has no public normative specification — the algorithm was confidential and licensed through ETSI. Every open implementation is reverse-engineered. Correctness is established by byte-exact agreement with libdvbcsa 1.1.0 (VideoLAN's reference free implementation): 11 golden vectors (184-byte TS payloads) plus inline multi-size vectors (8 B, 16 B, 32 B, 64 B).

Algorithm overview

DVB-CSA2 combines a block cipher and a stream cipher, both keyed by the same 8-byte control word:

Block cipher — 56-round substitution/permutation network on 8-byte blocks, applied in a CBC-like chained mode across all complete blocks.
Stream cipher — LFSR-based byte-stream generator seeded from the nibble-swapped control word and the encrypted first block as IV, XOR'd with bytes 8..end.

Encrypt = block CBC then stream XOR; decrypt = stream XOR then block CBC undo. Payloads shorter than 8 bytes pass through unchanged.

Usage

use dvb_csa::{ControlWord, scramble, descramble};

let cw = ControlWord::from_bytes([0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08]);

let mut payload = vec![0xAA; 184];
scramble(&cw, &mut payload);
descramble(&cw, &mut payload);
// payload is back to all 0xAA

For TS-packet-level operation (extracts the payload, respects the adaptation field):

use dvb_csa::{ControlWord, ts};

let cw = ControlWord::from_bytes([0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08]);
let mut packet = [0u8; 188];
// ... fill packet ...
let _ = ts::scramble_ts_packet(&cw, &mut packet);

Features

Feature	Default	What it does
`std`	yes	Enables `std::error::Error` on `Error`

Builds no_std without default features.

License