Collision Attack on the Waterfall Hash Function

We give a method that appears to be able to find colliding messages for the Waterfall hash function with approximately $O(2^{70})$ work for all hash sizes. If correct, this would show that the Waterfall hash function does not meet the required collision resistance

Quantum Cryptanalysis of NTRU

This paper explores some attacks that someone with a Quantum Computer may be able to perform against NTRUEncrypt, and in particular NTRUEncrypt as implemented by the publicly available library from Security Innovation. We show four attacks that an attacker with a Quantum Computer might be able to perform against encryption performed by this library. Two of these attacks recover the private key from the public key with less effort than expected; in one case taking advantage of how the published library is implemented, and the other, an academic attack that works against four of the parameter sets defined for NTRUEncrypt. In addition, we also show two attacks that are able to recover plaintext from the ciphertext and public key with less than expected effort. This has potential implications on the use of NTRU within TOR, as suggested by Whyte and Schanc

Further Analysis of a Proposed Hash-Based Signature Standard

We analyze the concrete security of a hash-based signature scheme described in the most recent Internet Draft by McGrew, Fluhrer and Curcio. We perform this analysis in the random-oracle model, where the Merkle-Damgård hash compression function is models as the random oracle. We show that, even with a large number of different keys the attacker can choose from, and a huge computational budget, the attacker succeeds in creating a forgery with negligible probability ($< 2^{-129}$)

Cryptanalysis of ring-LWE based key exchange with key share reuse

This paper shows how several ring-LWE based key exchange protocols can be broken, under the assumption that the same key share is used for multiple exchanges. This indicates that, if these key exchange protocols are used, then it will be necessary for a fresh key share be generated for each exchange, and that these key exchange protocols cannot be used as a drop in replacement for designs which use Diffie-Hellman static key shares

Multiple forgery attacks against Message Authentication Codes

Some message authentication codes (MACs) are vulnerable to multiple forgery attacks, in which an attacker can gain information that allows her to succeed in forging multiple message/tag pairs. This property was first noted in MACs based on universal hashing, such as the Galois/Counter Mode (GCM) of operation for block ciphers. However, we show that CBC-MAC and HMAC also have this property, and for some parameters are more vulnerable than GCM. We present multiple-forgery attacks against these algorithms, then analyze the security against these attacks by using the expected number of forgeries. We compare the different MACs using this measure. This document is a pre-publication draft manuscript

The Extended Codebook (XCB) Mode of Operation

We describe a block cipher mode of operation that implements a `tweakable\u27 (super) pseudorandom permutation with an arbitrary block length. This mode can be used to provide the best possible security in systems that cannot allow data expansion, such as disk-block encryption and some network protocols. The mode accepts an additional input, which can be used to protect against attacks that manipulate the ciphertext by rearranging the ciphertext blocks. Our mode is similar to a five-round Luby-Rackoff cipher in which the first and last rounds do not use the conventional Feistel structure, but instead use a single block cipher invocation. The third round is a Feistel structure using counter mode as a PRF. The second and fourth rounds are Feistel structures using a universal hash function; we re-use the polynomial hash over a binary field defined in the Galois/Counter Mode (GCM) of operation for block ciphers. This choice provides efficiency in both hardware and software and allows for re-use of implementation effort. XCB also has several useful properties: it accepts arbitrarily-sized plaintexts and associated data, including any plaintexts with lengths that are no smaller than the width of the block cipher. This document is a pre-publication draft manuscript

Leakage of Signal function with reused keys in RLWE key exchange

In this paper, we show that the signal function used in Ring-Learning with Errors (RLWE) key exchange could leak information to find the secret $s$ of a reused public key $p=as+2e$. This work is motivated by an attack proposed in \cite{cryptoeprint:2016:085} and gives an insight into how public keys reused for long term in RLWE key exchange protocols can be exploited. This work specifically focuses on the attack on the KE protocol in \cite{Ding} by initiating multiple sessions with the honest party and analyze the output of the signal function. Experiments have confirmed the success of our attack in recovering the secret

Pipelineable On-Line Encryption

Correct authenticated decryption requires the receiver to buffer the decrypted message until the authenticity check has been performed. In high-speed networks, which must handle large message frames at low latency, this behavior becomes practically infeasible. This paper proposes CCA-secure on-line ciphers as a practical alternative to AE schemes since the former provide some defense against malicious message modifications. Unfortunately, all published on-line ciphers so far are either inherently sequential, or lack a CCA-security proof. This paper introduces POE, a family of on-line ciphers that combines provable security against chosen-ciphertext attacks with pipelineability to support efficient implementations. POE combines a block cipher and an e-AXU family of hash functions. Different instantiations of POE are given, based on different universal hash functions and suitable for different platforms. Moreover, this paper introduces POET, a provably secure on-line AE scheme, which inherits pipelineability and chosen-ciphertext-security from POE and provides additional resistance against nonce-misuse attacks

Improved key recovery of level 1 of the Bluetooth Encryption System

The encryption system $E_{0}$, which is the encryption system used in the Bluetooth specification, is a two level system where a key and a packet nonce is given to a level 1 key stream generator, which produces the key for a level 2 key stream generator, whose output is used to encrypt. We give a method for recovering the key for the level 1 key stream generator given the internal keys for two or three level 2 key stream generators. This method, combined with published methods for recovering keys for the level 2 key stream generator, can be used to recover the $E_{0}$ second key with $O(2^{65})$ work, and $O(2^{80})$ precomputation time. Although this attack is of no advantage if $E_{0}$ is used with the recommended security parameters (64 bit encryption key), it shows that no addition security would be made available by enlarging the encryption key, as discussed in the Bluetooth specification