Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Phoenix: A Formally Verified Regenerating Vault   An attacker that gains access to a cryptocurrency user's private keys can
perform any operation in her stead. Due to the decentralized nature of most
cryptocurrencies, no entity can revert those operations. This is a central
challenge for decentralized systems, illustrated by numerous high-profile
heists. Vault contracts reduce this risk by introducing artificial delay on
operations, allowing abortion by the contract owner during the delay. However,
the theft of a key still renders the vault unusable and puts funds at risk.
  We introduce Phoenix, a novel contract architecture that allows the user to
restore its security properties after key loss. Phoenix takes advantage of
users' ability to store keys in easily-available but less secure storage
(tier-two) as well as more secure storage that is harder to access (tier-one).
Unlike previous solutions, the user can restore Phoenix security after the
theft of tier-two keys and does not lose funds despite losing keys in either
tier. Phoenix also introduces a mechanism to reduce the damage an attacker can
cause in case of a tier-one compromise.
  We formally specify Phoenix's required behavior and provide a prototype
implementation of Phoenix as an Ethereum contract. Since such an implementation
is highly sensitive and vulnerable to subtle bugs, we apply a formal
verification tool to prove specific code properties and identify faults. We
highlight a bug identified by the tool that could be exploited by an attacker
to compromise Phoenix. After fixing the bug, the tool proved the low-level
executable code's correctness.

14
The categories of this paper are: math-ph
34
The categories of this paper are: chem-ph
16
The categories of this paper are: stat
37
The categories of this paper are: supr-con
32
The categories of this paper are: atom-ph
3
The categories of this paper are: physics
26
The categories of this paper are: bayes-an
13
The categories of this paper are: quant-ph
33
The categories of this paper are: plasm-ph
20
The categories of this paper are: acc-phys
29
The categories of this paper are: funct-an
6
The categories of this paper are: astro-ph
35
The categories of this paper are: mtrl-th
0
The categories of this paper are: hep-ph
22
The categories of this paper are: chao-dyn
28
The categories of this paper are: alg-geom