## CryptoDB

### Reza Reyhanitabar

#### Publications

Year
Venue
Title
2021
TOSC
The currently ongoing NIST LWC project aims at identifying new standardization targets for lightweight authenticated encryption with associated data (AEAD) and (optionally) lightweight cryptographic hashing. NIST has deemed it important for performance and cost to be optimized on relevant platforms, especially for short messages. Reyhanitabar, Vaudenay and Vizár (Asiacrypt 2016) gave a formal treatment for security of nonce-based AEAD with variable stretch, i.e., when the length of the authentication tag is changed between encryptions without changing the key. They argued that AEAD supporting variable stretch is of practical interest for constrained applications, especially low-power devices operated by battery, due to the ability to flexibly trade communication overhead and level of integrity.In this work, we investigate this hypothesis with affirmative results. We present vCCM, a variable-stretch variant of the standard CCM and prove it is secure when used with variable stretch. We then experimentally measure the energy consumption of a real-world wireless sensor node when encrypting and sending messages with vCCM and CCM, respectively. Our projections show that the flexible trade of integrity level and ciphertext expansion can lead up to 21% overall energy consumption reduction in certain scenarios. As vCCM is obtained from the widely-used CCM by a black-box transformation, allowing any existing CCM implementations to be reused as-is, our results can be immediately put to use in practice. vCCM is all the more relevant because neither the NIST LWC project, nor any of the candidates give a consideration for the support of variable stretch and the related integrity-overhead trade-off.
2019
ASIACRYPT
Highly efficient encryption and authentication of short messages is an essential requirement for enabling security in constrained scenarios such as the CAN FD in automotive systems (max. message size 64 bytes), massive IoT, critical communication domains of 5G, and Narrowband IoT, to mention a few. In addition, one of the NIST lightweight cryptography project requirements is that AEAD schemes shall be “optimized to be efficient for short messages (e.g., as short as 8 bytes)”.In this work we introduce and formalize a novel primitive in symmetric cryptography called forkcipher. A forkcipher is a keyed primitive expanding a fixed-lenght input to a fixed-length output. We define its security as indistinguishability under a chosen ciphertext attack (for n-bit inputs to 2n-bit outputs). We give a generic construction validation via the new iterate-fork-iterate design paradigm.We then propose ${\mathsf {ForkSkinny}}$ as a concrete forkcipher instance with a public tweak and based on SKINNY: a tweakable lightweight cipher following the TWEAKEY framework. We conduct extensive cryptanalysis of ${\mathsf {ForkSkinny}}$ against classical and structure-specific attacks.We demonstrate the applicability of forkciphers by designing three new provably-secure nonce-based AEAD modes which offer performance and security tradeoffs and are optimized for efficiency of very short messages. Considering a reference block size of 16 bytes, and ignoring possible hardware optimizations, our new AEAD schemes beat the best SKINNY-based AEAD modes. More generally, we show forkciphers are suited for lightweight applications dealing with predominantly short messages, while at the same time allowing handling arbitrary messages sizes.Furthermore, our hardware implementation results show that when we exploit the inherent parallelism of ${\mathsf {ForkSkinny}}$ we achieve the best performance when directly compared with the most efficient mode instantiated with SKINNY.
2016
ASIACRYPT
2015
EPRINT
2015
EPRINT
2015
EPRINT
2015
FSE
2015
CRYPTO
2015
ASIACRYPT
2010
EPRINT
In this paper, we revisit security notions for dedicated-key hash functions, considering two essential theoretical aspects; namely, formal definitions for security notions, and the relationships among them. Our contribution is twofold. First, we provide a new set of enhanced security notions for dedicated-key hash functions. The provision of this set of enhanced properties has been motivated by the introduction of enhanced target collision resistance (eTCR) property by Halevi and Krawczyk at Crypto 2006. We notice that the eTCR property does not belong to the set of the seven security notions previously investigated by Rogaway and Shrimpton at FSE 2004, namely: Coll, Sec, aSec, eSec, Pre, aPre and ePre. The fact that eTCR, as a new useful property, is the enhanced variant of the well-known TCR (a.k.a. eSec or UOWHF) property motivates one to investigate the possibility of providing enhanced variants for the other properties. We provide such an enhanced set of properties. Interestingly, there are six enhanced variants of security notions available, excluding ePre'' which can be demonstrated to be non-enhanceable. As the second and main part of our contribution, we provide a full picture of relationships (i.e. implications and separations) among the (thirteen) security properties including the (six) enhanced properties and the previously considered seven properties. The implications and separations are supported by formal proofs (reductions) and/or counterexamples in the concrete-security framework.
2010
FSE
2009
EPRINT
Enhanced Target Collision Resistance (eTCR) property for a hash function was put forth by Halevi and Krawczyk in Crypto 2006, in conjunction with the randomized hashing mode that is used to realize such a hash function family. eTCR is a strengthened variant of the well-known TCR (or UOWHF) property for a hash function family (i.e. a dedicated-key hash function). The contributions of this paper are twofold. First, we compare the new eTCR property with the well-known collision resistance (CR) property, where both properties are considered for a dedicated-key hash function. We show there is a separation between the two notions, that is, in general, eTCR property cannot be claimed to be weaker (or stronger) than CR property for any arbitrary dedicated-key hash function. Second, we consider the problem of eTCR property preserving domain extension. We study several domain extension methods for this purpose, including (Plain, Strengthened, and Prefix-free) Merkle-Damg{\aa}rd, Randomized Hashing (considered in dedicated-key hash setting), Shoup, Enveloped Shoup, XOR Linear Hash (XLH), and Linear Hash (LH) methods. Interestingly, we show that the only eTCR preserving method is a nested variant of LH which has a drawback of having high key expansion factor. Therefore, it is interesting to design a new and efficient eTCR preserving domain extension in the standard model.
2009
FSE
2007
EPRINT
We present a new non-interactive message authentication protocol in manual channel model (NIMAP, for short) using the weakest assumption on the manual channel (i.e. assuming the strongest adversary). Our protocol uses enhanced target collision resistant (eTCR) hash family and is provably secure in the standard model. We compare our protocol with protocols with similar properties and show that the new NIMAP has the same security level as the best previously known NIMAP whilst it is more practical. In particular, to authenticate a message such as a 1024-bit public key, we require an eTCR hash family that can be constructed from any off-the-shelf Merkle-Damg{\aa}rd hash function using randomized hashing mode. The underlying compression function must be {\em evaluated second preimage resistant} (eSPR), which is a strictly weaker security property than collision resistance. We also revisit some closely related security notions for hash functions and study their relationships to help understanding our protocol.