[48998] in Cypherpunks
RC2 technical questions
daemon@ATHENA.MIT.EDU (baldwin)
Fri Feb 2 13:04:56 1996
Date: Fri, 02 Feb 96 10:02:37 PST
From: "baldwin" <baldwin@RSA.COM (Robert W. Baldwin)>
To: baldwin@RSA.COM (Robert W. Baldwin), cypherpunks@toad.com
In a shameless attempt to move the discussion of RC2 into
a more technical arena, here are some interesting questions to
explore about RC2.
--Bob
Key expansion
- How can you tell whether the permutation is based on
some sequence of digits from PI?
- What are the diffusion and avalanche properties of
this permutation?
- What are the linear characteristics of this permutation?
- What are the properties of the compression function
that maps 16 bits (bytes X and Y) to 8 bits (byte Z)
via Z = P[X + Y]?
- How does the length of the key influence the mixing
of bits during each pass of the expansion algorithm?
- Is this a non-linear feedback shift register over
the field GF(256)?
- If the first pass of expansion is viewed as a hash
function that produces 40 or 128 bits out, what are
its properties?
Round Functions
- What are the diffusion and avalanche properties of
the two round functions?
- What are the linear approximations and how good are they?
- What characteristics can be preserved by the round
function that performs rotations?
- With what probability?
- Does the amount of rotation influence the security?
- What characteristics can be preserved by the round
function that performs the data dependent selection
of the expanded key?
- With what probability?
- Are there any "weak" keys?
- Will the expansion algorithm produce them?
