Noninteractive two-channel message authentication based on hybrid-collision resistant hash functions.

We consider the problem of non-interactive message authentication using two channels: an insecure broadband channel and an authenticated narrow-band channel. This problem has been considered in the context of ad hoc networks, where it is assumed that there is neither a secret key shared among the two parties, nor a public-key infrastructure in place. We present a formal model for protocols of this type, along with a new protocol which is as efficient as the best previous protocols. The security of our protocol is based on a new property of hash functions that we introduce, which we name ``hybrid-collision resistance\u27\u27

Practical Unconditionally Secure Two-channel Message Authentication

We investigate unconditional security for message authentication protocols that are designed using two-channel cryptography. We look at both noninteractive message authentication protocols (NIMAPs) and interactive message authentication protocols (IMAPs). We provide a new proof of nonexistence of nontrivial unconditionally secure NIMAPs. This proof consists of a combinatorial counting argument and is much shorter than the previous proof by Wang et al., which was based on probability distribution arguments. Further, we propose a generalization of an unconditionally secure 3-round IMAP due to Naor, Segev and Smith. With a careful choice of parameters, our scheme improves that of Naor et al. Our scheme is very close to optimal for most parameter situations of practical interest.

Noninteractive Manual Channel Message Authentication Based On eTCR Hash Functions

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-Damgård 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

Dual channel-based network traffic authentication

In a local network or the Internet in general, data that is transmitted between two computers (also known as network traffic or simply, traffic) in that network is usually classified as being of a malicious or of a benign nature by a traffic authentication system employing databases of previously observed malicious or benign traffic signatures, i.e., blacklists or whitelists, respectively. These lists typically consist of either the destinations (i.e., IP addresses or domain names) to which traffic is being sent or the statistical properties of the traffic, e.g., packet size, rate of connection establishment, etc. The drawback with the list-based approach is its inability to offer a fully comprehensive solution since the population of the list is likely to go on indefinitely. This implies that at any given time, there is a likelihood of some traffic signatures not being present in the list, leading to false classification of traffic. From a security standpoint, whitelists are a safer bet than blacklists since their underlying philosophy is to block anything that is unknown hence in the worst case, are likely to result in high false rejects with no false accepts. On the other hand, blacklists block only what is known and therefore are likely to result in high false accepts since unknown malicious traffic will be accepted, e.g., in the case of zero-day attacks (i.e., new attacks whose signatures have not yet been analyzed by the security community). Despite this knowledge, the most commonly used traffic authentication solutions, e.g., antivirus or antimalware solutions, have predominantly employed blacklists rather than whitelists in their solutions. This can perhaps be attributed to the fact that the population of a blacklist typically requires less user involvement than that of a whitelist. For instance, malicious traffic signatures (i.e., behavior or destinations) are usually the same across a population of users; hence, by observing malicious activity from a few users, a global blacklist that is applicable to all users can be created. Whitelist generation, on the other hand, tends to be more user-specific as what may be considered acceptable or benign traffic to one user may not be considered the same to a different user. As a result, users are likely to find whitelist-based solutions that require their participation to be both cumbersome and inconveniencing. This dissertation offers a whitelist-based traffic authentication solution that reduces the active participation of users in whitelist population. By relying on activity that users regularly engage in while interacting with their computers (i.e., typing), we are able to identify legitimate destinations to which users direct their traffic and use these to populate the whitelist, without requiring the users to deviate from their normal behavior. Our solution requires users to type the destinations of their outgoing traffic requests only once, after which any subsequent requests to that destination are authenticated without the need for them to be typed again. Empirical results from testing our solution in a real time traffic analysis scenario showed that relatively low false reject rates for legitimate traffic with no false accepts for illegitimate traffic are achievable. Additionally, an investigation into the level of inconvenience that the typing requirement imposes on the users revealed that, since users are likely to engage in this (typing) activity during the course of utilizing their computer\u27s resources, this requirement did not pose a significant deterrent to them from using the system

Recognition in Ad Hoc Pervasive Networks

We examine the problem of message and entity recognition in the context of ad hoc networks. We review the definitions and the security model described in the literature and examine previous recognition protocols described in ABCLMN98, HWGW05, LZWW05, M03, and WW03. We prove that there is a one to one correspondence between non-interactive message recognition protocols and digital signature schemes. Hence, we concentrate on designing interactive recognition protocols. We look at LZWW05 in more detail and suggest a variant to overcome a certain shortcoming. In particular, in case of communication failure or adversarial disruption, this protocol is not equipped with a practical resynchronization process and can fail to resume. We propose a variant of this protocol which is equipped with a resynchronization technique that allows users to resynchronize whenever they wish or when they suspect an intrusion

Proofs of Quantumness from Trapdoor Permutations

Assume that Alice can do only classical probabilistic polynomial-time computing while Bob can do quantum polynomial-time computing. Alice and Bob communicate over only classical channels, and finally Bob gets a state $|x_0\rangle+|x_1\rangle$ with some bit strings $x_0$ and $x_1$. Is it possible that Alice can know $\{x_0,x_1\}$ but Bob cannot? Such a task, called {\it remote state preparations}, is indeed possible under some complexity assumptions, and is bases of many quantum cryptographic primitives such as proofs of quantumness, (classical-client) blind quantum computing, (classical) verifications of quantum computing, and quantum money. A typical technique to realize remote state preparations is to use 2-to-1 trapdoor collision resistant hash functions: Alice sends a 2-to-1 trapdoor collision resistant hash function $f$ to Bob, and Bob evaluates it coherently, i.e., Bob generates $\sum_x|x\rangle|f(x)\rangle$. Bob measures the second register to get the measurement result $y$, and sends $y$ to Alice. Bob\u27s post-measurement state is $|x_0\rangle+|x_1\rangle$, where $f(x_0)=f(x_1)=y$. With the trapdoor, Alice can learn $\{x_0,x_1\}$ from $y$, but due to the collision resistance, Bob cannot. This Alice\u27s advantage can be leveraged to realize the quantum cryptographic primitives listed above. It seems that the collision resistance is essential here. In this paper, surprisingly, we show that the collision resistance is not necessary for a restricted case: we show that (non-verifiable) remote state preparations of $|x_0\rangle+|x_1\rangle$ secure against {\it classical} probabilistic polynomial-time Bob can be constructed from classically-secure (full-domain) trapdoor permutations. Trapdoor permutations are not likely to imply the collision resistance, because black-box reductions from collision-resistant hash functions to trapdoor permutations are known to be impossible. As an application of our result, we construct proofs of quantumness from classically-secure (full-domain) trapdoor permutations

Message Authentication and Recognition Protocols Using Two-Channel Cryptography

We propose a formal model for non-interactive message authentication protocols (NIMAPs) using two channels and analyze all the attacks that can occur in this model. Further, we introduce the notion of hybrid-collision resistant (HCR) hash functions. This leads to a new proposal for a NIMAP based on HCR hash functions. This protocol is as efficient as the best previous NIMAP while having a very simple structure and not requiring any long strings to be authenticated ahead of time. We investigate interactive message authentication protocols (IMAPs) and propose a new IMAP, based on the existence of interactive-collision resistant (ICR) hash functions, a new notion of hash function security. The efficient and easy-to-use structure of our IMAP makes it very practical in real world ad hoc network scenarios. We also look at message recognition protocols (MRPs) and prove that there is a one-to-one correspondence between non-interactive MRPs and digital signature schemes with message recovery. Further, we look at an existing recognition protocol and point out its inability to recover in case of a specific adversarial disruption. We improve this protocol by suggesting a variant which is equipped with a resynchronization process. Moreover, another variant of the protocol is proposed which self-recovers in case of an intrusion. Finally, we propose a new design for message recognition in ad hoc networks which does not make use of hash chains. This new design uses random passwords that are being refreshed in each session, as opposed to precomputed elements of a hash chain

Algebraic Frameworks for Cryptographic Primitives

A fundamental goal in theoretical cryptography is to identify the conceptually simplest abstractions that generically imply a collection of other cryptographic primitives. For symmetric-key primitives, this goal has been accomplished by showing that one-way functions are necessary and sufficient to realize primitives ranging from symmetric-key encryption to digital signatures. By contrast, for asymmetric primitives, we have no (known) unifying simple abstraction even for a few of its most basic objects. Moreover, even for public-key encryption (PKE) alone, we have no unifying abstraction that all known constructions follow. The fact that almost all known PKE constructions exploit some algebraic structure suggests considering abstractions that have some basic algebraic properties, irrespective of their concrete instantiation. We make progress on the aforementioned fundamental goal by identifying simple and useful cryptographic abstractions and showing that they imply a variety of asymmetric primitives. Our general approach is to augment symmetric abstractions with algebraic structure that turns out to be sufficient for PKE and much more, thus yielding a “bridge” between symmetric and asymmetric primitives. We introduce two algebraic frameworks that capture almost all concrete instantiations of (asymmetric) cryptographic primitives, and we also demonstrate their applicability by showing their cryptographic implications. Therefore, rather than manually building different cryptosystems from a new assumption, one only needs to build one (or more) of our simple structured primitives, and a whole host of cryptosystems immediately follows.PHDComputer Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/166137/1/alamati_1.pd