Hash-based cryptography


The security of quantum-resistant cryptographic algorithms of this category is based on the properties of cryptographic hash functions. Among such properties we can distinguish ― resistance to the search for a prototype, collisions, the second prototype. Based on cryptographic hash functions, the electronic signature algorithm SPHINCS+ is an alternative participant in the third round of the NIST competition.

Among the features of this class of algorithms short public and secret keys can be distinguished as well as conservatism from the security point of view. Hash functions is a well-known and well-researched tool for building cryptographic schemes.
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New classes of algorithms are required to protect information systems from attacks using a quantum computer. Among such classes of algorithms, electronic signature schemes based on cryptographic hash functions are considered. A hash function is a function that maps an arbitrary amount of data into a fixed-length string in such a way that it is almost impossible to find an input that is displayed in a specific output. In such schemes, the following approach is used: a one-time signature scheme is taken as a basis (only one message can be signed), then it is combined with the Merkle tree to obtain a reusable signature. Several variations of the described approach are possible to achieve greater efficiency.

A feature of algorithms based on hash functions is the high confidence in their security. When constructing electronic signature schemes, evidence of the fact that the security of the scheme goes all about certain properties of cryptographic hash functions is used. This means that if the scheme is hacked, then some of the properties will be violated. It is important to note that the properties of cryptographic hash functions have been studied for many years, but if the hash function used in a particular protocol turns out to be unsafe, then it will be enough to replace it with another one, the design itself will remain unchanged.

From the implementation point of view, an important advantage of cryptosystems of this class is the ability to use current equipment. Most calculations involve hash function calculations. And for a large number of hash functions approved by NIST, there are or are being developed hardware optimizations at the level of processor instructions of various architectures.

The issues of creating encryption schemes and generating a key on hash functions remain open.

What actions are being taken today to use post-quantum cryptography based on hash functions?

The QApp team pays great attention to the development of cryptographic algorithms based on hash functions. Thus, our team members contributed to the proof of the security of the SPHINCS+ algorithm (an alternative candidate for NIST standardization).