Cipher

About: Cipher is a research topic. Over the lifetime, 9409 publications have been published within this topic receiving 110309 citations. The topic is also known as: cypher & cryptographic algorithm.

Post-Quantum Key Exchange for the TLS Protocol from the Ring Learning with Errors Problem

Abstract: Lattice-based cryptographic primitives are believed to offer resilience against attacks by quantum computers. We demonstrate the practicality of post-quantum key exchange by constructing cipher suites for the Transport Layer Security (TLS) protocol that provide key exchange based on the ring learning with errors (R-LWE) problem, we accompany these cipher suites with a rigorous proof of security. Our approach ties lattice-based key exchange together with traditional authentication using RSA or elliptic curve digital signatures: the post-quantum key exchange provides forward secrecy against future quantum attackers, while authentication can be provided using RSA keys that are issued by today's commercial certificate authorities, smoothing the path to adoption. Our cryptographically secure implementation, aimed at the 128-bit security level, reveals that the performance price when switching from non-quantum-safe key exchange is not too high. With our R-LWE cipher suites integrated into the Open SSL library and using the Apache web server on a 2-core desktop computer, we could serve 506 RLWE-ECDSA-AES128-GCM-SHA256 HTTPS connections per second for a 10 KiB payload. Compared to elliptic curve Diffie-Hellman, this means an 8 KiB increased handshake size and a reduction in throughput of only 21%. This demonstrates that provably secure post-quantum key-exchange can already be considered practical.

Midori: A Block Cipher for Low Energy

Abstract: In the past few years, lightweight cryptography has become a popular research discipline with a number of ciphers and hash functions proposed. The designers' focus has been predominantly to minimize the hardware area, while other goals such as low latency have been addressed rather recently only. However, the optimization goal of low energy for block cipher design has not been explicitly addressed so far. At the same time, it is a crucial measure of goodness for an algorithm. Indeed, a cipher optimized with respect to energy has wide applications, especially in constrained environments running on a tight power/energy budget such as medical implants. This paper presents the block cipher Midorii¾?The name of the cipher is the Japanese translation for the word Green. that is optimized with respect to the energy consumed by the circuit per bt in encryption or decryption operation. We deliberate on the design choices that lead to low energy consumption in an electrical circuit, and try to optimize each component of the circuit as well as its entire architecture for energy. An added motivation is to make both encryption and decryption functionalities available by small tweak in the circuit that would not incur significant area or energy overheads. We propose two energy-efficient block ciphers Midori128i¾?and Midori64i¾?with block sizes equal to 128 and 64 bits respectively. These ciphers have the added property that a circuit that provides both the functionalities of encryption and decryption can be designed with very little overhead in terms of area and energy. We compare our results with other ciphers with similar characteristics: it was found that the energy consumptions ofi¾?Midori64i¾? and Midori128i¾? are by far better when compared ciphers like PRINCE and NOEKEON.

Conditionally-perfect secrecy and a provably-secure randomized cipher

Abstract: Shannon's pessimistic theorem, which states that a cipher can be perfect only when the entropy of the secret key is at least as great as that of the plaintext, is relativized by the demonstration of a randomized cipher in which the secret key is short but the plaintext can be very long. This cipher is shown to be “perfect with high probability.” More precisely, the eavesdropper is unable to obtain any information about the plaintext when a certain security event occurs, and the probability of this event is shown to be arbitrarily close to one unless the eavesdropper performs an infeasible computation. This cipher exploits the assumed existence of a publicly-accessible string of random bits whose length is much greater than that of all the plaintext to be encrypted; this is a feature that our cipher has in common with the previously considered “book ciphers”. Two modifications of this cipher are discussed that may lead to practical provably-secure ciphers based on either of two assumptions that appear to be novel in cryptography, viz., the (sole) assumption that the enemy's memory capacity (but not his computing power) is restricted and the assumption that an explicit function is, in a specified sense, controllably-difficult to compute, but not necessarily one-way.

Security Weaknesses in Bluetooth

Abstract: We point to three types of potential vulnerabilities in the Bluetooth standard, version 1.0B. The first vulnerability opens up the system to an attack in which an adversary under certain circumstances is able to determine the key exchanged by two victim devices, making eavesdropping and impersonation possible. This can be done either by exhaustively searching all possible PINs (but without interacting with the victim devices), or by mounting a so-called middle-person attack. We show that one part of the key exchange protocol - an exponential back-off method employed in case of incorrect PIN usage - adds no security, but in fact benefits an attacker. The second vulnerability makes possible an attack - which we call a location attack - in which an attacker is able to identify and determine the geographic location of victim devices. This, in turn, can be used for industrial espionage, blackmail, and other undesirable activities. The third vulnerability concerns the cipher. We show two attacks on the cipher, and one attack on the use of the cipher. The former two do not pose any practical threat, but the latter is serious. We conclude by exhibiting a range of methods that can be employed to strengthen the protocol and prevent the newly discovered attacks. Our suggested alterations are simple, and are expected to be possible to be implemented without major modifications.