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As opposed to most previous high-performance software implementations of operation modes -- that have considered the encryption of single messages -- we propose to process multiple messages in parallel. We demonstrate that this message scheduling is of significant advantage for most modes. As a baseline for longer messages, the performance of AES-CBC encryption on a single core increases by factor 6.8 when adopting this approach.
For the first time, we report optimized AES-NI implementations of the novel AE modes OTR, McOE-G, COBRA, and POET -- both with single and multiple messages. For almost all AE modes considered, we obtain a consistent speed-up when processing multiple messages in parallel. Notably, among the nonce-based modes, AES-CCM gets by factor 3.5 faster and its performance is about 1.2 cpb which is close to that of AES-GCM (the latter, however, possessing classes of weak keys), with AES-OCB3 still performing at only 0.69 cpb. Among the nonce-misuse resistant modes, AES-McOE-G receives a speed-up by factor 4 and its performance is about 1.44 cpb, which is faster than AES-COBRA with its 1.55 cpb but slower than AES-COPA with 1.29 cpb.
The aim of the PhD project is to develop new quantum-cryptographic protocols (beyond the task of key distribution) and explore their possibilities and limitations. An example of an active research topic 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.
Preferred starting date is 1 September 2014 (or earlier if possible).
We systematically study the provable security of the TLS handshake, as
it is implemented and deployed. To capture the details of the standard and its main extensions, we rely on miTLS, a verified reference implementation of the protocol. miTLS inter-operates with mainstream browsers and servers for many protocol versions, configurations, and ciphersuites; and it provides application-level, provable security for some.
We propose new agile security definitions and assumptions for the signatures, key encapsulation mechanisms, and key derivation algorithms used by the TLS handshake. By necessity, our definitions are stronger than those expected with simple modern protocols.
To validate our model of key encapsulation, we prove that RSA
ciphersuites satisfy the security assumption needed for our proof of
the handshake. Specifically, we formalize the use of PKCS#1v1.5 encryption in TLS, including recommended countermeasures against Bleichenbacher attacks, and build a 3,000-line EasyCrypt proof of its security against replayable chosen-ciphertext attacks under the assumption that ciphertexts are hard to re-randomize.
Based on our new agile definitions, we construct a modular proof of security for the miTLS reference implementation of the handshake, including ciphersuite negotiation, key exchange, renegotiation, and resumption, treated as a detailed 3,600-line executable model.
We present our main definitions, constructions, and proofs for an abstract model of the protocol, featuring series of related runs of the handshake with different ciphersuites. We also describe its refinement to account for the whole reference implementation, based on automated verification tools.
Outcome of the research: Higher throughput of RC4 algorithm can be achieved in multicores when using the proposed mechanism in this research. Effective use of multithreading in encryption can be achieved in multicores using this technique.
The first three schemes are key-policy attribute-based encryption (KP-ABE) and the fourth scheme is ciphertext-policy attribute-based encryption (CP-ABE) scheme.
\\item Our first scheme has very compact ciphertexts. The ciphertext overhead only consists of two group elements and this is the shortest in the literature.
Compared to the scheme by Attrapadung et al. (PKC2011), which is the best scheme in terms of the ciphertext overhead, our scheme shortens ciphertext overhead by $33\\%$.
The scheme also reduces the size of the master public key to about half.
\\item Our second scheme is proven secure under the decisional bilinear Diffie-Hellman (DBDH) assumption, which is one of the most standard assumptions in bilinear groups. Compared to the non-monotonic KP-ABE scheme from the same assumption by Ostrovsky et al. (ACM-CCS\'07), our scheme achieves more compact parameters. The master public key and the ciphertext size is about the half that of their scheme.
\\item Our third scheme is the first non-monotonic KP-ABE scheme that can deal with unbounded size of set and access policies. That is, there is no restriction on the size of attribute sets and
the number of allowed repetition of the same attributes which appear in an access policy.
The master public key of our scheme is very compact: it consists of only constant number of group elements.
\\item Our fourth scheme is the first non-monotonic CP-ABE scheme that can deal with unbounded size of set and access policies. The master public key of the scheme consists of only constant number of group elements.
We construct our KP-ABE schemes in a modular manner.
We first introduce special type of predicate encryption that we call two-mode identity based broadcast encryption (TIBBE).
Then, we show that any TIBBE scheme that satisfies certain condition can be generically converted into non-monotonic KP-ABE scheme.
Finally, we construct efficient TIBBE schemes and apply this conversion to obtain the above new non-monotonic KP-ABE schemes.