493 research outputs found
New Lattice Attacks on DSA Schemes
We prove that a system of linear congruences of a particular form has
at most a unique solution below a certain bound which can be computed efficiently. Using this result we develop
attacks against the DSA schemes which, under some assumptions, can provide the secret key
in the case where one or several signed messages are available
Attacking (EC)DSA scheme with ephemeral keys sharing specific bits
In this paper, we present a deterministic attack on (EC)DSA signature scheme,
providing that several signatures are known such that the corresponding
ephemeral keys share a certain amount of bits without knowing their value. By
eliminating the shared blocks of bits between the ephemeral keys, we get a
lattice of dimension equal to the number of signatures having a vector
containing the private key. We compute an upper bound for the distance of this
vector from a target vector, and next, using Kannan's enumeration algorithm, we
determine it and hence the secret key. The attack can be made highly efficient
by appropriately selecting the number of shared bits and the number of
signatures
Integration of post-quantum cryptography in the TLS protocol (LWE Option)
Dissertação de mestrado em Computer ScienceWith the possibility of quantum computers making an appearance, possibly capable of
breaking several well established and widespread crytposystems (especially those that
implement public key cryptography), necessity has arisen to create new cryptographic
algorithms which remain safe even against adversaries using quantum computers.
Several algorithms based on different mathematical problems have been proposed which
are considered to be hard to solve with quantum computers. In recent years, a new
lattice-based mathematical problem called Learning With Errors (and its variant Ring -
Learning With Errors) was introduced, and several cryptosystems based on this problem
were introduced, some of which are becoming practical enough to compete with traditional
schemes that have been used for decades.
The primary focus in this work is the implementation of two Ring - Learning With Errors
based schemes (one key exchange mechanism and one digital signature scheme) on the TLS
protocol via the OpenSSL library as a way of checking their overall viability in real-world
scenarios, by comparing them to classical schemes implementing the same functionalities.Com a possibilidade do surgimento dos primeiros computadores quânticos, possivelmente
capazes de quebrar muitos dos cripto-sistemas bem difundidos e considerados seguros,
tornou-se necessário tomar precauções com a criação de novas técnicas criptográficas que
visam manter as suas propriedades de segurança mesmo contra adversários que usem
computadores quânticos.
Existem já muitas propostas de algoritmos baseados em problemas matemáticos
distintos que são considerados difíceis de resolver recorrendo a computadores quânticos.
Recentemente, foi introduzido um novo problema baseado em reticulados denominado de
Learning With Errors (e a sua variante Ring - Learning With Errors), e consequentemente
foram propostos vários cripto-sistemas baseados nesse problema, alguns dos quais começam
já a ser utilizáveis ao ponto de poderem ser comparados com os esquemas clássicos usados
há décadas.
O foco principal neste trabalho é a implementação de dois esquemas baseados no problema
Ring - Learning With Errors (mais precisamente, um esquema de troca de chaves e uma
assinatura digital) no protocolo TLS através da sua integração no OpenSSL como forma de
verificar a sua viabilidade em contextos reais, comparando-os com esquemas clássicos que
implementem as mesmas funcionalidades
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