rcsa

Pure Rust DVB Common Scrambling Algorithm (DVB-CSA) for MPEG transport streams.

• Descrambler: descrambles 188-byte TS packets in place with an even/odd control word pair. Payloads after an adaptation field and trailing partial blocks are handled; descrambled packets get their scrambling bits cleared.
• CsaBatch: bitsliced batch of full-payload packets, 64 lanes (u64), 128 lanes (SSE2, NEON) or 256 lanes (AVX2, detected at runtime). Decrypt and encrypt.
• Csa: one packet at a time, any payload length.

No dependencies; unsafe only in the SIMD backends and their dispatch.

Usage

use rcsa::Descrambler;

let mut descrambler = Descrambler::new();
descrambler.set_even(&cw[.. 8].try_into()?);
descrambler.set_odd(&cw[8 ..].try_into()?);

// a whole number of 188-byte packets; larger buffers are faster
descrambler.descramble(&mut packets);

When a new control word takes effect is up to the caller: set_even/set_odd replace the key immediately.

Performance

Descrambling real SD and HD channels, one core of a Xeon E5-2660 v3 (Haswell), buffers of 1024-4096 packets, payload Mbit/s. FFdecsa and libdvbcsa built with -O3 -msse2, rcsa with the default target (AVX2 picked at runtime):

	Mbit/s
rcsa	1230-1280
FFdecsa	1070-1090
libdvbcsa	750-765

Without AVX2 (SSE2) rcsa does about 980 Mbit/s on the same CPU.