*03:15* [Job][New]
Ph.D. student in Theoretical Computer Science, *CWI / University of Amsterdam*
The Institute for Logic, Language & Computation (ILLC) at the University of Amsterdam, and the Centrum Wiskunde & Informatica (CWI) are looking for a PhD candidate in the area of quantum cryptography.

The aim of the PhD project is to develop new quantum-cryptographic protocols (beyond the task of key distribution) and explore their limitations. An example of an active research is position-based quantum cryptography. Another aspect is to investigate the security of classical cryptographic schemes against quantum adversaries (post-quantum cryptography).

Full-time appointment is on a temporary basis for a period of four years. For the first two years the PhD candidate will be appointed at the ILLC, University of Amsterdam, initially for a period of 18 months and then, on positive evaluation, for a further six months. During the final two years, the PhD candidate will be employed by the Centrum Wiskunde and Informatica (CWI). On the basis of a full-time appointment (38 hours per week), the gross monthly salary amounts to €2,083 during the first year, rising to €2,664 during the fourth year.

Requirements:

- a Master\'s degree with excellent grades in computer science, mathematics or physics with outstanding results or a comparable degree;
- candidates with a strong background in cryptography or quantum information are preferred;
- demonstrated research abilities by completion of an (undergraduate) research project;
- good academic writing and presentation skills;
- good social and organisational skills.

*21:17* [Pub][ePrint]
HIMMO security, by Oscar Garcia-Morchon and Ronald Rietman and Ludo Tolhuizen and Domingo Gomez-Perez and Jaime Gutierrez
This paper describes HIMMO, an identity-based pairwise symmetric key establishment method. The acronym \"HIMMO\" is derived from two interpolation problems that are essential for thesecurity of the scheme: the HI problem, which is related to the

well-known noisy interpolation problem, and the apparently novel MMO problem, presented at ISSAC\'14.

HIMMO is non-interactive: nodes in a network can directly generate a common key without exchanging messages. Each node in the network has an identifier, and a trusted third pay (TTP) provides it with secret keying material---linked to the node identifier---in a secure way.

A node that wishes to communicate with another node uses its own secret keying material and the identity of the other node to generate a common pairwise key.

HIMMO allows for efficient operation with respect to both the amount of stored keying material and the key computation time, which is especially relevant for resource-constrained devices.

It has similar operational characteristics as previous ID-based symmetric key establishment methods, but has superior resistance against attacks in which multiple colluding or compromised nodes co-operate to obtain information on keys between other non-colluding or non-compromised nodes.

*21:17* [Pub][ePrint]
Bounded Pre-Image Awareness and the Security of Hash-Tree Keyless Signatures, by Ahto Buldas and Risto Laanoja and Peeter Laud and Ahto Truu
We present a new tighter security proof for unbounded hash tree keyless signature (time-stamping) schemes that use Merkle-Damg\\aa rd (MD) hash functions with Preimage Aware (PrA) compression functions. It is known that the PrA assumption alone is insufficient for proving the security of unbounded hash tree schemes against back-dating attacks. We show that many known PrA constructions satisfy a stronger \\emph{Bounded Pre-Image Awareness (BPrA)} condition that assumes the existence of an extractor $\\EXT$ that is bounded in the sense that for any efficiently computable query string $\\alpha$, the number of outputs $y$ for which $\\EXT(y,\\alpha)$ succeeds does not exceed the number of queries in $\\alpha$. We show that blockcipher based MD-hash functions with rate-1 compression functions (such as Davies-Meyer and Miyaguchi-Preneel) of both type I and type II are BPrA. We also show that the compression function of Shrimpton-Stam that uses non-compressing components is BPrA. The security proof for unbounded hash-tree schemes is very tight under the BPrA assumption. In order to have $2^s$-security against back-dating, the hash function must have $n=2s + 4$ output bits, assuming that the security of the hash function is close to the birthday barrier, i.e. that there are no structural weaknesses in the hash function itself. Note that the previous proofs that assume PrA gave the estimation $n=2s + 2 \\log_2 C + 2$, where $C$ is the maximum allowed size of the hash tree. For example, if $s=100$ ($2^{100}$-security) and $C=2^{50}$, the previous proofs require $n=302$ output bits, while the new proof requires $n=204$ output bits.