Brussels / 4 & 5 February 2017


Interview with Gilles Van Assche
Portfolio of optimized cryptographic functions based on Keccak

Photo of Gilles Van Assche

Gilles Van Assche will give a talk about Portfolio of optimized cryptographic functions based on Keccak at FOSDEM 2017.

Q: Could you briefly introduce yourself?

I am a cryptographer working at STMicroelectronics. Together with my colleagues of the Keccak team, I enjoy working on new cryptographic functions with an eye towards simplicity and efficiency.

Q: What will your talk be about, exactly? Why this topic?

I would like to present a set of Keccak-based functions that covers the full range of symmetric cryptography functionality, from hashing to authenticated encryption. There will be different aspects.

For instance, one aspect will be to start from the concept of a pseudo-random function (PRF) and to show how flexible it is for achieving authentication and confidentiality. I will then show how to instantiate these, not only with sponge and duplex constructions (as in our CAESAR proposals Ketje and Keyak), but also with a brand new construction called Farfalle.

Another aspect is to discuss the delicate trade-off between performance and safety margin. In this respect, we as Keccak team have tried to address the increasing need for parallelism in order to achieve good performance on modern processors.

I think that these topics are relevant when building or improving security systems. In general, cryptography is a living subject, and it is therefore important to discuss these innovations and new trends in general.

Q: What do you hope to accomplish by giving this talk? What do you expect?

Symmetric cryptography relies on public scrutiny and third-party cryptanalysis. NIST specifically addressed this by organizing an open competition and by involving a wide community. Because of its selection as SHA-3, one of Keccak’s strengths is that it attracted a lot of attention. With this talk, I hope to show that Keccak builds up on this strength when its role is extended beyond hashing. Also, I hope that people will think twice when selecting a cryptographic algorithm, especially if it was designed behind closed doors (like DES, SHA-1 and SHA-2).

Q: Since its selection as the SHA-3 standard (NIST’s FIPS 202), Keccak has grown out of its mere hashing functionality. What cryptographic functions are possible with the Keccak permutation now? Did you know all those applications when you were designing the Keccak algorithm? Or did you only discover some of them later?

Keccak, and permutation-based cryptography in general, is still evolving. When we designed Keccak in 2007-2008, we had not yet seen that the sponge construction could also be used for authenticated encryption. Recently, Bart Mennink, Reza Reyhanitabar and Damian Vizár proved that one can securely increase the throughput with full-state absorbing. So we decided to exploit it in our authenticated encryption scheme Keyak.

Now, we just published a new permutation-based construction called Farfalle, which can be seen as a parallel counterpart of the sponge. In addition to its efficiency advantages on high-end CPUs, Farfalle allows us to easily build new kinds of (authenticated) encryption schemes, including a wide block cipher.

Q: What’s the status of your Keccak Code Package? Which functionality is already available?

We reworked the Keccak Code Package (KCP) quite extensively in 2016 to make it as easy to use as possible and to allow different kinds of functions to co-exist. Thanks to a clean separation between the low-level functions (like the permutation) and high-level user-oriented functions, it supports optimized implementations for several platforms.

At this time of writing, the KCP supports hashing (FIPS 202, Keccak and KangarooTwelve), a pseudo-random bit generator (KeccakPRG) and authenticated encryption (Ketje and Keyak). It also supports functions from the draft SP 800-185 standard (cSHAKE, ParallelHash), but we haven’t found the time yet to update them to comply to the official standard that was just released last December.

We also started implementing Kravatte, the instantiation of Farfalle with the Keccak permutation, and we hope to be ready by FOSDEM (or soon after).

Q: How can interested developers contribute to the Keccak Code Package? For which tasks could you use some manpower?

If someone wishes to implement the new functions from the SP 800-185 standard that was officially released recently, that would be welcome (and also a smooth way of diving into it).

We would also be happy to add implementations on platforms that we don’t currently support.

Q: Where is Keccak used at the moment?

The earliest adopter of significant size is the 3rd Generation Partnership Project (3GPP), aimed at specifying the next generation cellular system. They defined the TUAK algorithms for mobile phone authentication in SIM cards, based on Keccak, before the release of the FIPS 202 standard.

Of course, Keccak is at the heart of NIST’s FIPS 202 (SHA-3) standard, and more recently, of the SP 800-185 standard. It is difficult to answer exhaustively who is using those standards, but according to the list of NIST-validated implementations, there are some major industrial players.

Regarding open-source projects, one can find many implementations of Keccak/SHA-3 in different languages. Also, the standard library of Python 3.6 natively supports the FIPS 202 instances.

Q: Suppose I want to use Keccak, Ketje, Keyak or KangarooTwelve in my software. Where do I start? Is it difficult to use the Keccak Code Package?

That is easy. From the KCP, you just type make generic64/libkeccak.a and you get a library containing those functions, compiled from code generically optimized for 64-bit processors. Of course, you can replace generic64 by generic32 for 32-bit code, or by Haswell, ARMv7A, etc., for code more aggressively optimized for those platforms.

Q: Have you enjoyed previous FOSDEM editions?

I have attended and enjoyed all FOSDEM editions since 2012. Thanks for organizing this great open-source event!

Creative Commons License
Creative Commons License

This interview is licensed under a Creative Commons Attribution 2.0 Belgium License.