Chapter 9 - Example for an Algebraic Attack on a Symmetric Stream Cipher

Question 1

What is an algebraic attack?

Answer 1

Reduce encryption problem to a polynomial equations, in best case linear

Question 2

How can A5/2 be attacked using an algebraic attack?

Answer 2

• 8 frames cypher-text required
• Due to GSM error correction being calculated before encryption, its possible the retrieve the key stream
• With 8 frames of keystream its possible to get Kc as it is the initial state of the registers