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IEEE International Symposium on Information Theory (ISIT)

Information-theoretic Key Encapsulation and its Application to Secure Communication

Setareh Sharifian, Reihaneh Safavi–Naini

Published Jul 12, 2021• 6 citations
Publisher

Abstract

A hybrid encryption scheme consists of a public-key part called the key encapsulation mechanism (KEM), that is used to generate and establish a shared secret key between two parties, and a (symmetric) secret-key part called the data encapsulation mechanism (DEM) that encrypts the data using the shared key. Hybrid encryption schemes are widely used for securing Internet communication. In this paper, we initiate the study of hybrid encryption in preprocessing model which assumes access to initial correlated variables by all parties (including the eavesdropper), and define information-theoretic KEM (iKEM) that together with a (computationally) secure DEM, results in a hybrid encryption scheme in preprocessing model. We define security of each building block, and prove a composition theorem that guarantees (computational) q-chosen-plaintext attack (CPA) security of the hybrid encryption system if the iKEM and the DEM satisfy q-chosen-encapsulation attack security and one-time security, respectively. We show that an iKEM can be realized by an information-theoretic one-way secret key agreement (OW-SKA) protocol where a single message is transmitted from Alice to Bob, with a new security definition that allows$q$queries to Alice. Using a OW-SKA that satisfies this new definition of security, effectively allows the established secret key to be used with a onetime symmetric key encryption system that can be implemented, for example, by XORing the output of a (computationally) secure pseudorandom generator with the message, to provide secure encryption of$q$arbitrary messages (polynomially bounded length). We discuss our results and directions for future work.

DOI
10.1109/isit45174.2021.9517958

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A hybrid encryption scheme consists of a public-key part called the key encapsulation mechanism (KEM), that is used to generate and establish a shared secret key between two parties, and a (symmetric) secret-key part called the data encapsulation mechanism (DEM) that encrypts the data using the shared key. Hybrid encryption schemes are widely used for securing Internet communication. In this paper, we initiate the study of hybrid encryption in preprocessing model which assumes access to initial correlated variables by all parties (including the eavesdropper), and define information-theoretic KEM (iKEM) that together with a (computationally) secure DEM, results in a hybrid encryption scheme in preprocessing model. We define security of each building block, and prove a composition theorem that guarantees (computational) q-chosen-plaintext attack (CPA) security of the hybrid encryption system if the iKEM and the DEM satisfy q-chosen-encapsulation attack security and one-time security, respectively. We show that an iKEM can be realized by an information-theoretic one-way secret key agreement (OW-SKA) protocol where a single message is transmitted from Alice to Bob, with a new security definition that allowsqqqqueries to Alice. Using a OW-SKA that satisfies this new definition of security, effectively allows the established secret key to be used with a onetime symmetric key encryption system that can be implemented, for example, by XORing the output of a (computationally) secure pseudorandom generator with the message, to provide secure encryption ofqqqarbitrary messages (polynomially bounded length). We discuss our results and directions for future work.
A hybrid encryption scheme is a public-key encryption system that consists of a public-key part called the key encapsulation mechanism (KEM), and a (symmetric) secret-key part called data encapsulation mechanism (DEM): the public-key part is used to generate a shared secret key between two parties, and the symmetric key part is used to encrypt the message using the generated key. Hybrid encryption schemes are widely used for secure communication over the Internet. In this paper, we initiate the study of hybrid encryption in preprocessing model which assumes access to initial correlated variables by all parties (including the eavesdropper). We define information-theoretic KEM (iKEM) that, together with a (computationally) secure DEM, results in a hybrid encryption scheme in preprocessing model. We define the security of each building block, and prove a composition theorem that guarantees (computational) qe-chosen plaintext (CPA) security of the hybrid encryption system if the iKEM and the DEM satisfy qe-chosen encapculation attack and one-time security, respectively. We show that iKEM can be realized by a one-way SKA (OW-SKA) protocol with a revised security definition. Using an OW-SKA that satisfies this revised definition of security effectively allows the secret key that is generated by the OW-SKA to be used with a one-time symmetric key encryption system such as XORing a pseudorandom string with the message, and provide qe-CPA security for the hybrid encryption system.We discuss our results and directions for future work.
A hybrid encryption scheme uses a key encapsulation mechanism (KEM) to generate and establish a shared secret key with the decrypter, and a secret key data encapsulation mechanism (DEM) to encrypt the data using the key that is established by the DEM. The decrypter recovers the key using the ciphertext that is generated by the KEM, and uses it to decrypt the ciphertext that is generated by the DEM.We motivate and propose hybrid encryption in correlated randomness model where all participants including the eavesdropper, have access to samples of their respective correlated random variables. We define information-theoretic KEM (iKEM), and prove a composition theorem for iKEM and DEM that allows us to construct an efficient hybrid encryption system in correlated randomness model, providing post-quantum security. The construction uses an information-theoretic one-way secret key agreement (OW-SKA) protocol that satisfies a new security definition, and a one-time symmetric key encryption system that can be implemented by XORing the output of a (computationally) secure pseudorandom generator with the message. We discuss our results and directions for future work.
A hybrid encryption (HE) system is an efficient public key encryption system for arbitrarily long messages. An HE system consists of a public key component called key encapsulation mechanism (KEM), and a symmetric key component called data encapsulation mechanism (DEM). The HE encryption algorithm uses a KEM generated key k to encapsulate the message using DEM, and send the ciphertext together with the encapsulaton of k, to the decryptor who decapsulates k and uses it to decapsulate the message using the corresponding KEM and DEM components. The KEM/DEM composition theorem proves that if KEM and DEM satisfy well-defined security notions, then HE will be secure with well defined security. We introduce HE in correlated randomness model where the encryption and decryption algorithms have samples of correlated random variables that are partially leaked to the adversary. Security of the new KEM/DEM paradigm is defined against computationally unbounded or polynomially bounded adversaries. We define iKEM and cKEM with respective information theoretic computational security, and prove a composition theorem for them and a computationally secure DEM, resulting in secure HEs with proved computational security (CPA and CCA) and without any computational assumption. We construct two iKEMs that provably satisfy the required security notions of the composition theorem. The iKEMs are used to construct two efficient quantum-resistant HEs when used with an AES based DEM. We also define and construct combiners with proved security that combine the new KEM/DEM paradigm of HE with the traditional public key based paradigm of HE.
Quantum key distribution (QKD) allows Alice and Bob to share a secret key with proven information-theoretic security. Composability-based security proofs for QKD ensure that using the established key to encrypt a message using a one-time-pad encryption system, will result in information-theoretic secrecy for the communication. In this paper, we consider the problem of using a QKD established key with a secure symmetrickey based encryption system with computational security, and use an extension of the framework of hybrid encryption to prove security of the composition. We use an extension of the original framework of hybrid encryption to correlated randomness setting (Sharifian et al. in ISIT 2021) and propose a quantum-enabled Key Encapsulation Mechanism (qKEM) that is used to construct a quantum-enabled hybrid encryption (qHEq H EqHE) system, 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 scheme for unrestricted length messages with proved security against an adversary with access to (efficient) quantum computations. Thus a key-efficient post-quantum secure encryption with proved security and without using any computational assumptions.
Abstract. Following the work of Al-Riyami et al. we define the notion of key encapsulation mechanism supporting cryptographic workflow (WF-KEM) and prove a KEM-DEM composition theorem which extends the notion of hybrid encryption to cryptographic workflow. We then generically construct a WF-KEM from an identity-based encryption (IBE) scheme and a secret sharing scheme. Chosen ciphertext security is achieved using one-time signatures. Adding a public-key encryption scheme we are able to modify the construction to obtain escrow-freeness. We prove all our constructions secure in the standard model. Keywords. Cryptographic Workflow. Key Encapsulation. Secret Sharing. Identity-Based Encryption.
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. This 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 security guarantees depending on the properties of DEM-CD. When DEM-CD is one-time information-theoretically secure, the composition provides information-theoretic security for both encryption and certified deletion. When DEM-CD is computationally secure, the composed construction provides computationally secure (post-quantum) encryption and everlasting certified deletion, where confidentiality is computational until the deletion certificate is successfully verified. After successful verification, confidentiality becomes unconditional. That is, successful verification of the deletion certificate guarantees that the data has been removed information-theoretically from the adversary's view. Both pHE-CD constructions support the encryption of arbitrarily long messages. Construction 2 is key-efficient and uses a DEM-CD built from quantum coding and AES, providing quantum-safe security for encryption. We conclude by discussing the implications of our results and directions for future research.