Chosen-plaintext attack

Summary

A chosen-plaintext attack (CPA) is an attack model for cryptanalysis which presumes that the attacker can obtain the ciphertexts for arbitrary plaintexts. The goal of the attack is to gain information that reduces the security of the encryption scheme. Modern ciphers aim to provide semantic security, also known as ciphertext indistinguishability under chosen-plaintext attack, and they are therefore, by design, generally immune to chosen-plaintext attacks if correctly implemented. Introduction In a chosen-plaintext attack the adversary can (possibly adaptively) ask for the ciphertexts of arbitrary plaintext messages. This is formalized by allowing the adversary to interact with an encryption oracle, viewed as a black box. The attacker’s goal is to reveal all or a part of the secret encryption key. It may seem infeasible in practice that an attacker could obtain ciphertexts for given plaintexts. However, modern cryptography is implemented in software or hardware and is used

Official source

https://en.wikipedia.org/wiki/Chosen-plaintext_attack

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HELEN: A Public-Key Cryptosystem Based on the LPN and the Decisional Minimal Distance Problems

Alexandre Raphaël Duc, Serge Vaudenay

We propose HELEN, a code-based public-key cryptosystem whose security is based on the hardness of the Learning from Parity with Noise problem (LPN) and the decisional minimum distance problem. We show that the resulting cryptosystem achieves indistinguishability under chosen plaintext attacks (IND-CPA security). Using the Fujisaki-Okamoto generic construction, HELEN achieves IND-CCA security in the random oracle model. Our cryptosystem looks like the Alekhnovich cryptosystem. However, we carefully study its complexity and we further propose concrete optimized parameters.

Springer2013

HELEN: a Public-key Cryptosystem Based on the LPN Problem (Extended Abstract)

Alexandre Raphaël Duc, Serge Vaudenay

We propose HELEN, a new code-based public-key cryptosystem whose security is based on the hardness of the Learning from Parity with Noise problem~(LPN) and the decisional minimum distance problem. We show that the resulting cryptosystem achieves indistinguishability under chosen plaintext attacks (IND-CPA security). Using the Fujisaki-Okamoto generic construction, HELEN achieves IND-CCA security in the random oracle model. We further propose concrete parameters.

2012

Cryptanalysis of a Homomorphic Encryption Scheme

Sonia Mihaela Bogos, John Gaspoz, Serge Vaudenay

Homomorphic encryption allows to make specific operations on private data which stays encrypted. While applications such as cloud computing require to have a practical solution, the encryption scheme must be secure. In this article, we detail and analyze in-depth the homomorphic encryption scheme proposed by Zhou and Wornell in~\cite{zhou}. From the analysis of the encryption scheme, we are able to mount three attacks. The first attack enables to recover a secret plaintext message broadcasted to multiple users. The second attack performs a chosen ciphertext key recovery attack and it was implemented and verified. The last attack is a related chosen plaintext decryption attack.

2016