Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Problems and solutions of the Fourth International Students' Olympiad in
  Cryptography NSUCRYPTO   Mathematical problems and their solutions of the Fourth International
Students' Olympiad in cryptography NSUCRYPTO'2017 are presented. We consider
problems related to attacks on ciphers and hash functions, cryptographic
Boolean functions, the linear branch number, addition chains, error correction
codes, etc. We discuss several open problems on algebraic structure of
cryptographic functions, useful proof-of-work algorithms, the Boolean hidden
shift problem and quantum computings.

3
The categories of this paper are: physics
34
The categories of this paper are: chem-ph
29
The categories of this paper are: funct-an
13
The categories of this paper are: quant-ph
12
The categories of this paper are: nucl-th
28
The categories of this paper are: alg-geom
2
The categories of this paper are: math
36
The categories of this paper are: cmp-lg
6
The categories of this paper are: astro-ph
35
The categories of this paper are: mtrl-th
30
The categories of this paper are: q-alg
33
The categories of this paper are: plasm-ph
21
The categories of this paper are: adap-org
0
The categories of this paper are: hep-ph
15
The categories of this paper are: nucl-ex
7
The categories of this paper are: hep-th