Editing Common Scrambling Algorithm (section)

== Description of the cipher ==
The CSA algorithm is composed of two distinct ciphers: a block cipher and a stream cipher.

When used in encryption mode the data are first encrypted using the 64-bit block cipher in [[Block cipher modes of operation|CBC mode]], starting from packet end.
The stream cipher is then applied from packet start.

=== Block cipher ===

The block cipher process 64-bit blocks in 56 rounds. It uses 8 bits from an expanded key on each round.

[[Image:Dvbcsa block encrypt.svg|border|480px|Block cipher encryption]]

=== Stream cipher ===

The first 32 round of the stream cipher are used for initialization and do not generate any output.
The first 64 bits of data are used as [[initialization vector]] during this phase and are left unchanged.
The stream cipher then generates 2 bits of pseudo-random stream on each round which are xored starting at bit 64 of the packet.

[[File:Dvbcsa stream.svg|800px|border|Stream cipher details]]