5 votes

What does $(a+b) \bmod{256}$ and $a$ XOR $b$ reveal about $a, b$?

fgrieu analyzes the average case; we can also consider the worst case - how much the entropy are we guaranteed to have left. One 'worse case' happens if the $a+b = 0 \pmod {256}$ and $a \oplus b = 0$; ...
user avatar
  • 131k
4 votes

What does $(a+b) \bmod{256}$ and $a$ XOR $b$ reveal about $a, b$?

As I didn't see it mentioned yet: $a + b = (a\oplus b) + ((a\&b)<<1) \bmod 256$ (where $<<$ denotes left-shift), so the information you are given is equivalent to knowing $a\oplus b$ ...
4 votes
Accepted

What does $(a+b) \bmod{256}$ and $a$ XOR $b$ reveal about $a, b$?

I'll assume bitstrings are assimilated to integers by big-endian notation, $a$ and $b$ are $k$-bits with $k=8$ in the question, and it's given two $k$-bit quantities $s:=a+b\bmod{2^k}$ and $x:=a\oplus ...
user avatar
  • 122k
3 votes

predict random keys using python

We hope that's impossible; urandom is supposed to use a cryptographically strong random number generator, and so (without the internal rng state) we hope that you can't do it.
user avatar
  • 131k
2 votes
Accepted

For any numbers $a, b$, what are the operators $X, Y$ such that revealing $a\ X\ b$ and $a\ Y\ b$ doesn't reveal info about $a,b$?

It is possible to leak zero information. Assume uniformly distributed $a$ and $b$ and let $a$ vary along the rows and $b$ along the columns of the operation tables below: $$ \begin{array}{ccc} \begin{...
user avatar
  • 16.1k
2 votes

predict random keys using python

It might be possible to write a program that has some success with this if the program executes a side-channel attack on the underlying pseudorandom generator of /dev/urandom. If the system that we ...
user avatar
1 vote

What is the effect of low rank dual sublattices on the dual lattice attack on LWE?

This is not an answer. In the hope of assisting anybody thinking about this and in light of @TMM's comment, here's a little bit more flesh around the statement "Intuitively, one feels that if $\...
user avatar
  • 9,596

Only top scored, non community-wiki answers of a minimum length are eligible