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Reihaneh Safavi-Naini

Reihaneh Safavi-Naini appears in the imported research catalog. Authorship, coauthor and topic links are available while profile ownership is still unclaimed.

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Cryptography and SecurityInformation Theorymath.ITMachine LearningMultiagent Systemsquant-ph

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Published work

17 published item(s)

preprint2026arXiv

Hybrid Encryption with Certified Deletion in Preprocessing Model

Certified deletion allows Alice to outsource data to Bob and, at a later time, obtain a verifiable guarantee that the file has been irreversibly deleted at her request. The functionality, while impossible using classical information alone, can be achieved using quantum information. Existing approaches rely either on one-time pad (OTP) encryption, or on computational hardness assumptions that may be vulnerable to future advances in classical or quantum computing. In this work, we introduce and formalize hybrid encryption with certified deletion in the preprocessing model (pHE-CD) and propose two constructions. Each construction composes an information-theoretic key encapsulation mechanism (iKEM) with a data encapsulation mechanism that provides certified deletion (DEM-CD) security, offering different types of security depending on the security properties of DEM-CD. When DEM-CD is one-time information theoretically secure, the composition provides {\em information-theoretic security} for both encryption and certified deletion. When DEM-CD is computationally secure, the composed construction offers computationally secure (post-quantum) encryption and {\em everlasting certified deletion} where confidentiality is computational up to the point that the deletion certificate is verified, and after successful verification of the certificate, becomes unconditional. That is, successful verification of deletion certificate guarantees that the data has been removed information-theoretically from the adversary's view. Both pHE-CD schemes are for encryption of arbitrarily long messages. Construction 2 is key efficient and uses a DEM-CD that is constructed using quantum coding and AES, providing quantum-safe security for encryption. We discuss our results and directions for future work.

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preprint2026arXiv

MAGIQ: A Post-Quantum Multi-Agentic AI Governance System with Provable Security

Our computing ecosystem is being transformed by two emerging paradigms: the increased deployment of agentic AI systems and advancements in quantum computing. With respect to agentic AI systems, one of the most critical problems is creating secure governing architectures that ensure agents follow their owners' communication and interaction policies and can be held accountable for the messages they exchange with other agents. With respect to quantum computing, existing systems must be retrofitted and new cryptographic mechanisms must be designed to ensure long-term security and quantum resistance. In fact, NIST recommends that standard public-key cryptographic algorithms, including RSA, Diffie-Hellman (DH), and elliptic-curve constructions (ECC), be deprecated starting in 2030 and disallowed after 2035. In this paper, we present MAGIQ, a framework for policy definition and enforcement in multi-agent AI systems using novel, highly efficient, quantum-resistant cryptographic protocols with proven security guarantees. MAGIQ (i) allows users to define rich communication and access-control policy budgets for agent-to-agent sessions and tasks, including global budgets for one-to-many agent sessions; (ii) enforces such policies using post-quantum cryptographic primitives; (iii) supports session-based enforcement of policies for agent-to-agent and one-to-many agent sessions; and (iv) provides accountability of agents to their users through message attribution. We formally model and prove the correctness and security of the system using the Universal Composability (UC) framework. We evaluate the computation and communication overhead of our framework and compare it with the state-of-the-art agentic AI framework SAGA. MAGIQ is a first step toward post-quantum-secure solutions for agentic AI systems.

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preprint2025arXiv

Secure Composition of Quantum Key Distribution and Symmetric Key Encryption

Quantum key distribution (QKD) allows Alice and Bob to share a secret key over an insecure channel with proven information-theoretic security against an adversary whose strategy is bounded only by the laws of physics. Composability-based security proofs of QKD ensure that using the established key with a one-time-pad encryption scheme provides information theoretic secrecy for the message. In this paper, we consider the problem of using the QKD established key with a secure symmetric key-based encryption algorithm and use an approach based on hybrid encryption to provide a proof of security for the composition. Hybrid encryption was first proposed as a public key cryptographic algorithm with proven security for messages of unrestricted length. We use an extension of this framework to correlated randomness setting (Sharifian et al. in ISIT 2021) to propose a quantum-enabled Key Encapsulation Mechanism (qKEM) and quantum-enabled hybrid encryption (qHE), and prove a composition theorem for the security of the qHE. We construct a qKEM with proven security using an existing QKD (Portmann et al. in Rev. of Mod. Physics 2022). Using this qKEM with a secure Data Encapsulation Mechanism (DEM), that can be constructed using a one-time symmetric key encryption scheme, results in an efficient encryption system for unrestricted length messages with proved security against an adversary with access to efficient computations on a quantum computer (i.e. post-quantum secure encryption without using any computational assumptions.)

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preprint2022arXiv

Wiretap Secret Key Capacity of Tree-PIN

We consider the problem of multiterminal secret key agreement (SKA) in wiretapped source model where terminals have access to samples of correlated random variables from a publicly known joint probability distribution. The adversary has access to a side information variable, that is correlated with terminals' variables. We focus on a special type of terminal variables in this model, known as Tree-PIN, where the relation between variables of the terminals can be represented by a tree. The study of Tree-PIN source model is of practical importance as it can be realized in wireless network environments. We derive the wiretap secret key capacity of Tree-PIN with independent leakage, and give lower and upper bounds on the maximum achievable secret key length in finite-length regime. We then prove an upper bound and a lower bound for the wiretap secret key capacity of a wiretapped PIN and give two conditions for which these bounds are tight. We also extend our main result to two other related models and prove their corresponding capacities. At the end, we argue how our analysis suggests that public interaction is required for achieving the multiterminal WSK capacity.

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preprint2020arXiv

A Capacity-achieving One-message Key Agreement With Finite Blocklength Analysis

Information-theoretic secret key agreement (SKA) protocols are a fundamental cryptographic primitive that are used to establish a shared secret key between two or more parties. In a two-party SKA in source model, Alice and Bob have samples of two correlated variables, that are partially leaked to Eve, and their goal is to establish a shared secret key by communicating over a reliable public channel. Eve must have no information about the established key. In this paper, we study the problem of one-message secret key agreement where the key is established by Alice sending a single message to Bob. We propose a one-message SKA (OM-SKA) protocol, prove that it achieves the one-way secret key capacity, and derive finite blocklength approximations of the achievable secret key length. We compare our results with existing OM-SKAs and show the protocol has a unique combination of desirable properties.

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preprint2020arXiv

A Channel Model of Transceivers for Multiterminal Secret Key Agreement

Information theoretic secret key agreement is impossible without making initial assumptions. One type of initial assumption is correlated random variables that are generated by using a noisy channel that connects the terminals. Terminals use the correlated random variables and communication over a reliable public channel to arrive at a shared secret key. Previous channel models assume that each terminal either controls one input to the channel, or receives one output variable of the channel. In this paper, we propose a new channel model of transceivers where each terminal simultaneously controls an input variable and observes an output variable of the (noisy) channel. We give upper and lower bounds for the secret key capacity (i.e., highest achievable key rate) of this transceiver model, and prove the secret key capacity under the conditions that the public communication is noninteractive and input variables of the noisy channel are independent.

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preprint2020arXiv

Traceable Policy-Based Signatures and Instantiation from Lattices

Policy-based signatures (PBS) were proposed by Bellare and Fuchsbauer (PKC 2014) to allow an {\em authorized} member of an organization to sign a message on behalf of the organization. The user's authorization is determined by a policy managed by the organization's trusted authority, while the signature preserves the privacy of the organization's policy. Signing keys in PBS do not include user identity information and thus can be passed to others, violating the intention of employing PBS to restrict users' signing capability. In this paper, we introduce the notion of {\em traceability} for PBS by including user identity in the signing key such that the trusted authority will be able to open a suspicious signature and recover the signer's identity should the needs arise. We provide rigorous definitions and stringent security notions of traceable PBS (TPBS), capturing the properties of PBS suggested by Bellare-Fuchsbauer and resembling the "full traceability" requirement for group signatures put forward by Bellare-Micciancio-Warinschi (Eurocrypt 2003). As a proof of concept, we provide a modular construction of TPBS, based on a signature scheme, an encryption scheme and a zero-knowledge proof system. Furthermore, to demonstrate the feasibility of achieving TPBS from concrete, quantum-resistant assumptions, we give an instantiation based on lattices.

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preprint2016arXiv

Detecting Algebraic Manipulation in Leaky Storage Systems

Algebraic Manipulation Detection (AMD) Codes detect adversarial noise that is added to a coded message and stored in a storage that is opaque to the adversary. We study AMD codes when the storage can leak up to ρ\log|G| bits of information about the stored codeword, where G is the group in which the stored codeword lives and ρis a constant. We propose ρ-AMD codes that provide protection in this new setting, and define weak and strong ρ-AMD codes that provide security for a random and an arbitrary message, respectively. We derive concrete and asymptotic bounds for the efficiency of these codes featuring a rate upper bound of 1-ρfor the strong codes. We also define the class of ρ^{LV}-AMD codes that provide protection when leakage is in the form of a number of codeword components, and give constructions featuring a strong ρ^{LV}-AMD codes that asymptotically achieve the rate 1-ρ. We describe applications of ρ-AMD codes to, (i) robust ramp secret sharing scheme and, (ii) wiretap II channel when the adversary can eavesdrop a ρfraction of codeword components and tamper with all components of the codeword.

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preprint2016arXiv

Information-theoretically Secure Key Agreement over Partially Corrupted Channels

Key agreement is a fundamental cryptographic primitive. It has been proved that key agreement protocols with security against computationally unbounded adversaries cannot exist in a setting where Alice and Bob do not have dependent variables and communication between them is fully public, or fully controlled by the adversary. In this paper we consider this problem when the adversary can "partially" control the channel. We motivate these adversaries by considering adversarial corruptions at the physical layer of communication, give a definition of adversaries that can "partially" eavesdrop and "partially" corrupt the communication. We formalize security and reliability of key agreement protocols, derive bounds on the rate of key agreement, and give constructions that achieve the bound. Our results show that it is possible to have secret key agreement as long as some of the communicated symbols remain private and unchanged by the adversary. We relate our results to the previous known results, and discuss future work.

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preprint2015arXiv

Adversarial Wiretap Channel with Public Discussion

Wyner's elegant model of wiretap channel exploits noise in the communication channel to provide perfect secrecy against a computationally unlimited eavesdropper without requiring a shared key. We consider an adversarial model of wiretap channel proposed in [18,19] where the adversary is active: it selects a fraction $ρ_r$ of the transmitted codeword to eavesdrop and a fraction $ρ_w$ of the codeword to corrupt by "adding" adversarial error. It was shown that this model also captures network adversaries in the setting of 1-round Secure Message Transmission [8]. It was proved that secure communication (1-round) is possible if and only if $ρ_r + ρ_w <1$. In this paper we show that by allowing communicants to have access to a public discussion channel (authentic communication without secrecy) secure communication becomes possible even if $ρ_r + ρ_w >1$. We formalize the model of \awtppd protocol and for two efficiency measures, {\em information rate } and {\em message round complexity} derive tight bounds. We also construct a rate optimal protocol family with minimum number of message rounds. We show application of these results to Secure Message Transmission with Public Discussion (SMT-PD), and in particular show a new lower bound on transmission rate of these protocols together with a new construction of an optimal SMT-PD protocol.

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preprint2014arXiv

A Model for Adversarial Wiretap Channel

In wiretap model of secure communication the goal is to provide (asymptotic) perfect secrecy and reliable communication over a noisy channel that is eavesdropped by an adversary with unlimited computational power. This goal is achieved by taking advantage of the channel noise and without requiring a shared key. The model has attracted attention in recent years because it captures eavesdropping attack in wireless communication. The wiretap adversary is a passive eavesdropping adversary at the physical layer of communication. In this paper we propose a model for adversarial wiretap (AWTP) channel that models active adversaries at this layer. We consider a $(ρ_r, ρ_w)$ wiretap adversary who can see a fraction $ρ_r$, and modify a fraction $ρ_w$, of the sent codeword. The code components that are read and/or modified can be chosen adaptively, and the subsets of read and modified components in general, can be different. AWTP codes provide secrecy and reliability for communication over these channels. We give security and reliability definitions and measures for these codes, and define secrecy capacity of an AWTP channel that represents the secrecy potential of the channel. The paper has two main contributions. First, we prove a tight upper bound on the rate of AWTP codes with perfect secrecy for $(ρ_r, ρ_w)$-AWTP channels, and use the bound to derive the secrecy capacity of the channel. We prove a similar bound for $ε$-secure codes also, but in this case the bound is not tight. Second, we give an explicit construction for a capacity achieving AWTP code family, and prove its security and efficiency properties. We show that AWTP model is a natural generalization of Wyner's wiretap models and somewhat surprisingly, also provides a direct generalization for a seemingly unrelated cryptographic primitive, Secure Message Transmission (SMT).

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preprint2014arXiv

Efficient Codes for Adversarial Wiretap Channels

In [13] we proposed a (ρ_r , ρ_w )-adversarial wiretap channel model (AWTP) in which the adversary can adaptively choose to see a fraction ρ_r of the codeword sent over the channel, and modify a fraction ρ_w of the codeword by adding arbitrary noise values to them. In this paper we give the first efficient construction of a capacity achieving code family that provides perfect secrecy for this channel.

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preprint2014arXiv

Multipath Private Communication: An Information Theoretic Approach

Sending private messages over communication environments under surveillance is an important challenge in communication security and has attracted attentions of cryptographers through time. We believe that resources other than cryptographic keys can be used for communication privacy. We consider private message transmission (PMT) in an abstract multipath communication model between two communicants, Alice and Bob, in the presence of an eavesdropper, Eve. Alice and Bob have pre-shared keys and Eve is computationally unbounded. There are a total of $n$ paths and the three parties can have simultaneous access to at most $t_a$, $t_b$, and $t_e$ paths. The parties can switch their paths after every $λ$ bits of communication. We study perfect (P)-PMT versus asymptotically-perfect (AP)-PMT protocols. The former has zero tolerance of transmission error and leakage, whereas the latter allows for positive error and leakage that tend to zero as the message length increases. We derive the necessary and sufficient conditions under which P-PMT and AP-PMT are possible. We also introduce explicit P-PMT and AP-PMT constructions. Our results show AP-PMT protocols attain much higher information rates than P-PMT ones. Interestingly, AP-PMT is possible even in poorest condition where $t_a=t_b=1$ and $t_e=n-1$. It remains however an open question whether the derived rates can be improved by more sophisticated AP-PMT protocols. We study applications of our results to private communication over the real-life scenarios of multiple-frequency links and multiple-route networks. We show practical examples of such scenarios that can be abstracted by the multipath setting: Our results prove the possibility of keyless information-theoretic private message transmission at rates $17\%$ and $20\%$ for the two example scenarios, respectively. We discuss open problems and future work at the end.

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preprint2013arXiv

Efficient Codes for Limited View Adversarial Channels

We introduce randomized Limited View (LV) adversary codes that provide protection against an adversary that uses their partial view of the communication to construct an adversarial error vector to be added to the channel. For a codeword of length N, the adversary selects a subset of ρ_rN of the codeword components to "see", and then "adds" an adversarial error vector of weight ρ_wN to the codeword. Performance of the code is measured by the probability of the decoder failure in recovering the sent message. An (N, q^{RN},δ)-limited view adversary code ensures that the success chance of the adversary in making decoder fail, is bounded by δwhen the information rate of the code is at least R. Our main motivation to study these codes is providing protection for wireless communication at the physical layer of networks. We formalize the definition of adversarial error and decoder failure, construct a code with efficient encoding and decoding that allows the adversary to, depending on the code rate, read up to half of the sent codeword and add error on the same coordinates. The code is non-linear, has an efficient decoding algorithm, and is constructed using a message authentication code (MAC) and a Folded Reed-Solomon (FRS) code. The decoding algorithm uses an innovative approach that combines the list decoding algorithm of the FRS codes and the MAC verification algorithm to eliminate the exponential size of the list output from the decoding algorithm. We discuss application of our results to Reliable Message Transmission problem, and open problems for future work.

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preprint2013arXiv

Secure Distance Bounding Verification using Physical-Channel Properties

We consider the problem of distance bounding verification (DBV), where a proving party claims a distance and a verifying party ensures that the prover is within the claimed distance. Current approaches to "secure" distance estimation use signal's time of flight, which requires the verifier to have an accurate clock. We study secure DBV using physical channel properties as an alternative to time measurement. We consider a signal propagation environment that attenuates signal as a function of distance, and then corrupts it by an additive noise. We consider three attacking scenarios against DBV, namely distance fraud (DFA), mafia fraud (MFA) and terrorist fraud (TFA) attacks. We show it is possible to construct efficient DBV protocols with DFA and MFA security, even against an unbounded adversary; on the other hand, it is impossible to design TFA-secure protocols without time measurement, even with a computationally-bounded adversary. We however provide a TFA-secure construction under the condition that the adversary's communication capability is limited to the bounded retrieval model (BRM). We use numerical analysis to examine the communication complexity of the introduced DBV protocols. We discuss our results and give directions for future research.

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preprint2010arXiv

New Results on Secret Key Establishment over a Pair of Broadcast Channels

The problem of Secret Key Establishment (SKE) over a pair of independent Discrete Memoryless Broadcast Channels (DMBCs) has already been studied in \cite{Ah10}, where we provided lower and upper bounds on the secret-key capacity. In this paper, we study the above setup under each of the following two cases: (1) the DMBCs have secrecy potential, and (2) the DMBCs are stochastically degraded with independent channels. In the former case, we propose a simple SKE protocol based on a novel technique, called Interactive Channel Coding (ICC), and prove that it achieves the lower bound. In the latter case, we give a simplified expression for the lower bound and prove a single-letter capacity formula under the condition that one of the legitimate parties sends only i.i.d. variables.

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preprint2010arXiv

Secret Key Establishment over a Pair of Independent Broadcast Channels

This paper considers the problem of information-theoretic Secret Key Establishment (SKE) in the presence of a passive adversary, Eve, when Alice and Bob are connected by a pair of independent discrete memoryless broadcast channels in opposite directions. We refer to this setup as 2DMBC. We define the secret-key capacity in the 2DMBC setup and prove lower and upper bounds on this capacity. The lower bound is achieved by a two-round SKE protocol that uses a two-level coding construction. We show that the lower and the upper bounds coincide in the case of degraded DMBCs.

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