Stream Ciphers

Responsible

Lecture

Time & Place

17-20, 25-26 March 2008
Monday-Friday, Tuesday-Wednesday 9⁰⁰-18⁰⁰.

Start: Monday 17 March at 9.00 in the b-it Rheinsaal.

Stream ciphers constitute an important class of secret-key encryption algorithms. In fact, LFSR-based stream ciphers are widely used in many applications
because of the advantages they present compared to other encryption schemes, for instance, block ciphers: they are faster, require less hardware circuitry
and have fewer propagation errors. An example is Bluetooth encryption.

Stream ciphers consist of a seed, corresponding to the shared secret key, and a pseudorandom generator, which consists of constituent LFSRs and a nonlinear combination function. The result is a pseudo-random binary sequence, called the keystream, which is, in the case of a binary additive stream cipher, bitwise added to the plaintext in order to obtain the ciphertext. Hence, attacks on stream ciphers have as ultimate goal the recovery of theinitializations of the LFSRs.

Topics include

Study and implementation of LFSRs, important components in many stream ciphers.
Design principles of stream ciphers.
Attacks on stream ciphers.
Application: the Bluetooth stream cipher.

Course Material

Literature

Handbook of applied cryptography (Chapter 2, Chapter 6).
Stream Ciphers (a survey by Matt Robshaw).

Allocation

Equivalent 2+2 SWS.

Participants

There are exactly 20 places.

Language

The course will be held in English.