Crypt: Cryptanalysis

2019 / 01 / 17

Scientific leaders: Dr. Ronald CRAMER (CWI); Dr. Xiaoyun WANG (Tsinghua)

LIAMA founding members involved: Inria (France), Tsinghua (China), CWI (Netherlands)

LIAMA associated members involved: AMSS (China)

Host: Tsinghua

Creation: October 2011

Project Description

The focus of this project is cryptanalysis, which is traditionally defined as the art of code-breaking: cryptanalysis studies the best attacks on cryptographic schemes, from a theoretical point of view (algorithm design) but also from a practical of view (implementation, side-channel attacks). Cryptanalysis has a significant impact in the real world, because cryptographic algorithms and protocols, as well as keysizes, are selected based on the state-of-the-art in cryptanalysis, and are widely deployed in many applications: banking cards, subway cards, mobile phones, video games, pay TV, internet security, e-passports, bitcoin, car keys, DVDs and blu-ray, e-stamps, etc.

While the field of provable security has made great advances in the past thirty years, it is alone insufficient to select cryptographic parameters: in general, choosing parameters based purely on security proofs leads to rather inefficient schemes. Cryptanalysis is therefore complementary of provable security, and both are essential to our understanding of security.

The CRYPT project considers cryptanalysis in the two worlds of cryptography: public-key cryptography (also called asymmetric cryptography) and secret-key cryptography (also called symmetric cryptography). Secret-key cryptography is much more efficient (and therefore more widespread) than public-key cryptography, but also less powerful because it requires to share secret keys: it encompasses symmetric encryption (stream ciphers, block ciphers), message authentication codes, and hash functions. Public-key cryptography provides more functionalities such as digital signatures, identity-based encryption and more generally functional encryption. Current public-key cryptographic techniques are based on advanced mathematics such as number theory (e.g. elliptic curves and lattices).

Inside public-key cryptanalysis, we study lattice techniques in particular, because lattice-based cryptography has been attracting considerable interest in the past few years, due to unique features such as potential resistance to quantum computers and new functionalities such as fully-homomorphic encryption (which allows to compute on encrypted data without requiring secret keys, and can theoretically be used to secure cloud computing), noisy multi-linear maps and even very recently (indistinguishability) obfuscation.

Inside secret-key cryptanalysis, we study standard hash functions and the five SHA-3 finalists, due to the importance of the SHA-3 competition for a new hash function standard. We also study symmetric ciphers, including the AES block cipher standard and the widely deployed RC4 stream cipher.

As a side objective, this project also aims at developing European-Chinese collaboration in cryptologic research, such as by promoting scientific visits.


• Principal investigators: Dr. Ronald CRAMER (CWI),  Dr. Phong NGUYEN (Inria); Dr. Xiaoyun WANG (Tsinghua University).

• Other permanent members: Dr. Serge Fehr and Dr. Marc Stevens (CWI); Dr.Yingpu Deng and Dr.Yanbin Pan (AMSS); Dr.Hongbo Yu and Dr.KetingJia (Tsinghua).


The CRYPT project was created in October 2011 and has already obtained substantial results. As an example, CRYPT members gave in 2012 a complete break of the well-known NTRU signature scheme with countermeasures: this (patented) signature scheme is one of the most efficient signature algorithms known, and it was submitted to IEEE standardization. In practice, the attack developed by CRYPT can efficiently extract the secret key given only a few thousand signatures. CRYPT also developed more efficient attacks on several fully-homomorphic encryption schemes.


The publications of the CRYPT project can be found here on HAL.

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