GGHLite: More Efficient Multilinear Maps from Ideal Lattices, by Adeline Langlois and Damien Stehle and Ron Steinfeld
The GGH Graded Encoding Scheme, based on ideal lattices, is the first plausible approximation to a cryptographic multilinear map. Unfortunately, using the security analysis in the original paper, the scheme requires very large parameters to provide security for its underlying encoding re-randomization process. Our main contributions are to formalize, simplify and improve the efficiency and the security analysis of the re-randomization process in the GGH construction. This results in a new construction that we call GGHLite. In particular, we first lower the size of a standard deviation parameter of the re-randomization process of the original scheme from exponential to polynomial in the security parameter. This first improvement is obtained via a finer security analysis of the
drowning step of re-randomization, in which we apply the
Rényi divergence instead of the conventional statistical distance as a measure of distance between distributions. Our second improvement is to reduce the number of randomizers needed from $\\Omega(n \\log n)$ to $2$, where $n$ is the dimension of the underlying ideal lattices. These two contributions allow us to decrease the bit size of the public parameters from $O(\\lambda^5 \\log \\lambda)$ for the
GGH scheme to $O(\\lambda \\log^2 \\lambda)$ in GGHLite, with respect to the security parameter $\\lambda$ (for a constant multilinearity parameter $\\kappa$).
Software Security Engineer, CloudFlare Inc.
CloudFlare is looking for a talented software engineer to join our security team. We are working on a number of ambitious projects to secure the web and protect our customers from threats of all sorts. The role of security engineer at CloudFlare is more that of a builder than a breaker. You will have to approach problems with creativity and flexibility and be able to identify and use the best tools for the job or build better ones from scratch. At CloudFlare, we are serious about protecting our customers and advancing the state of the art in computer security.
We are looking for experienced engineers (5+ years of experience preferred) with practical expertise in the areas of:Web Security (web application firewall, authentication, anti-crawler technology, penetration testing)Security Intelligence (IP reputation, machine learning techniques using security data)Systems Security and Trusted Computing (application sandboxing, secure boot, remote attestation, TPMs)Secure Computation and Storage (encrypted databases, data anonymization, secure multi-party computation)Network Security Protocols (DNSSEC, SSL/TLS, SPDY, QUIC, etc.)Applied Cryptography (white-box cryptography, side-channel attacks)
Requirements:Proficiency in C, Go and/or Lua or willingness to learnExperience working on large scale distributed systems and performance-critical applicationsDesire to create well-crafted software
Bonus Points:Contributions to the open source communityUnderstanding of Linux internalsFamiliarity with compilers or code generation toolsHealthy sense of paranoia
Lei Wei: Analysis of Iterated Block Ciphers
Name: Lei Wei
Topic: Analysis of Iterated Block Ciphers
A block cipher is the foundation stone of symmetric-key cryptography. Due to its simplicity and high performance, it is often the workhorse for providing confidentiality - one of the primary goals of cryptography. Hence the security of a block cipher is of fundamental importance in the entire infrastructure of cryptography, and therefore block ciphers shall be analyzed and evaluated. This practice is called block cipher cryptanalysis. In this thesis, we analyze a few block ciphers in the classic meet-in-the-middle model and in the recently proposed
multidimensional linear cryptanalysis model.
Besides for encryption, block ciphers are also one of the most versatile building blocks used for constructing many other cryptographic primitives. One such example is the compression function of cryptographic hash functions, and there is a close relation between the security analysis of block ciphers and hash functions. In addition, many dedicated cryptographic hash functions are designed with ideas used in block ciphers. Therefore, it is natural that many block cipher
cryptanalysis techniques can be transferred to hash function analysis. In this thesis, we analyze hash functions with differential cryptanalysis and techniques inspired by differential cryptanalysis. On the other hand, recent advances in hash function cryptanalysis contribute to the analysis of block ciphers. We give one such example too.
In total we have four main topics on (or closely related to) the security analysis of block ciphers.
- We study the multidimensional extension to Matsui’s Algorithm 1 and find improvements that lower the attack’s costs. The new attacks are applied to 9-round and 4-round Serpent, with interesting observations on these improvements and the framework.
- We study meet-in-the-middle attacks and their application to the hardware-oriented block cipher Ktantan family and reduced DES. Several recent hash function analysis techniques are used f[...]