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Properties of AEAD algorithms
CryptoPro
andbogc@gmail.com
General
Network Working Group
authenticated encryption, mode of operation, AEAD, properties
Authenticated Encryption with Associated Data (AEAD) algorithms provide confidentiality and integrity of data. The extensive use of AEAD algorithms
in various high-level applications has caused the need for AEAD algorithms with additional properties and motivated research in the area. This document gives definitions
for the most common of those properties intending to improve consistency in the field.
Introduction
An Authenticated Encryption with Associated Data (AEAD) algorithm is an extension of authenticated encryption, which provides confidentiality for the plaintext to be encrypted
and integrity for the plaintext and some Associated Data (sometimes called Header). AEAD algorithms are used in numerous applications and have become an important field in cryptographic research.
Background
AEAD algorithms are formally defined in . The main benefit of AEAD algorithms is that they provide both data confidentiality and data integrity
and have a simple unified interface.
The importance of the AEAD algorithms is mainly explained by their exploitation simplicity: they have a unified interface, easy-to-understand security guarantees, and are much easier to implement
properly than MAC and encryption schemes separately. Therefore, their embedding into high-level schemes and protocols is highly transparent since, for example, there is no need for additional key
derivation procedures. Apart from that, when using the AEAD algorithm, it is possible to reduce the key and state sizes and improve the data processing speed. For instance, such algorithms are mandatory
for TLS 1.3 , IPsec ESP , and QUIC .
Hence, the research and standardization efforts in the field are extremely active. Most AEAD algorithms usually come with security guarantees, formal proofs, usage guidelines, and reference implementations.
Even though providing core properties of AEAD algorithms is enough for use in many applications, some environments require other unusual cryptographic properties, which commonly require additional analysis
and research. With the growing number of such properties and research papers, misunderstanding and confusion inevitably appear. Some properties might be understood in different ways, for some only non-trivial
formal security notions are provided, others require modification or extension of the standard AEAD interface to support additional functionality. Therefore, the risk of misuse of AEAD algorithms increases which
can lead to security issues.
Scope
In the following document, we provide a short overview of the most common properties of AEAD algorithms, by giving high-level definitions of these properties
in . The document aims to improve clarity and establish a common language in the field.
Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted
as described in BCP 14 when, and only when,
they appear in all capitals, as shown here.
AEAD properties
Security properties
Confidentiality
Definition. An AEAD algorithm guarantees that data is available only to those authorized to obtain it. That property is required for the AEAD
algorithm to be called secure.
Synonyms. Privacy.
Further reading. ,
Data integrity
Definition. An AEAD algorithm guarantees that data has not been changed or forged by those who are not authorized to.
That property is required for the AEAD algorithm to be called secure.
Synonyms. Message authentication.
Further reading. ,
Blockwise security
Definition. An AEAD algorithm provides security even if an adversary can adaptively choose the next block of the plaintext (ciphertext)
depending on already computed blocks of the ciphertext (plaintext) during an encryption (decryption) operation.
Further reading. ,
Key Dependent Messages (KDM) security
Definition. An AEAD algorithm provides security even when key-dependent plaintexts are encrypted.
Notes. KDM-security is achievable only if nonces are chosen randomly and associated data is key-independent.
Further reading.
Key commitment
Definition. An AEAD algorithm guarantees that it is difficult to find a tuple of the nonce, associated data, and ciphertext such that
it can be decrypted correctly with more than one key.
Synonyms. Key-robustness, key collision resistance.
Further reading. , ,
Leakage resistance
Definition. An AEAD algorithm provides security even if some additional information about computations of an encryption (and possibly decryption)
operation is obtained via side-channel leakages.
Further reading. ,
Multi-user security
Definition. An AEAD algorithm security level degrades sublinearly in the number of users. Here the level of security is understood in the sense of Authenticated Encryption Advantage (AEA)
as given in .
Further reading.
Nonce misuse
Definition. An AEAD algorithm provides security (resilience or resistance) even if an adversary can repeat nonces in its encryption queries.
Nonce misuse resilience
Definition. Security is provided only for messages encrypted with unique nonces.
Further reading. ,
Nonce misuse resistance
Definition. Security is provided for all messages.
Further reading.
Reforgeability resilience
Definition. An AEAD algorithm guarantees that once a successful forgery for the algorithm has been found, it is still hard to find any subsequent forgery.
Further reading. ,
Release of unverified plaintext (RUP) security
Definition. An AEAD algorithm provides security even if the plaintext is released for every ciphertext, including those with failed integrity verification.
Further reading.
Implementation properties
Inverse-free
Definition. A block cipher-based AEAD algorithm can be securely implemented without evaluating the block cipher inverse.
Lightweight
Definition. An AEAD algorithm can be efficiently and securely implemented on resource-constrained devices. In particular, it meets the criteria required in the NIST
Lightweight Cryptography competition .
Further reading.
Online
Definition. An AEAD algorithm encryption (decryption) operation can be implemented with a constant memory and a single one-direction pass over the plaintext (ciphertext),
writing out the result during that pass.
Further reading.
Parallelizable
Definition. An AEAD algorithm can fully exploit the parallel computation infrastructure.
Further reading.
Single pass
Definition. An AEAD algorithm encryption (decryption) operation can be implemented with a single pass over the plaintext (ciphertext).
Static Associated Data
Definition. An AEAD algorithm allows pre-computation for static (or repeating) associated data so that static AD doesn't significantly contribute to the computational
cost of encryption.
ZK-friendly
Definition. An AEAD algorithm operates on binary and prime fields with a low number of non-linear operations (often called multiplicative complexity). Thus, it allows efficient
implementation using a domain-specific language (DSL) for writing zk-SNARKs circuits.
Synonyms. ZK-focused, Arithmetization-oriented, Low Multiplicative Complexity
Further reading.
Additional functionality properties
Incremental
Definition. An AEAD algorithm allows encrypting a message, which only partly differs from some other previously encrypted message, faster than processing it from scratch.
Further reading. ,
Nonce-hiding
Definition. An AEAD algorithm decryption operation doesn't need the nonce value to perform the decryption. Thus, the algorithm provides privacy for the nonce value.
Further reading.
Remotely-keyed
Definition. An AEAD algorithm can be securely implemented with most of the operations in encryption/decryption performed by an insecure (i.e., it leaks all intermediate values) device,
which has no access to the key, while another secure device performs operations involving the key.
Further reading. ,
Robust
Definition. An AEAD algorithm allows the user to choose an arbitrary value l >= 0 for every plaintext and then encrypts it into a ciphertext, which is l bits longer.
Further reading.
Security Considerations
This document defines the properties of AEAD algorithms. However, the document does not describe any concrete mechanisms providing these properties, neither it describes how
to achieve them. In fact, one can claim that an AEAD algorithm provides any of the defined properties only if its analysis in the relevant models was carried out.
IANA Considerations
This document has no IANA actions.
References
Normative References
Informative References
Authenticated-encryption with associated-data.
Proceedings of the 9th ACM conference on Computer and communications security (CCS '02)
Association for Computing Machinery, New York, NY, USA, 98–107
Authenticated Encryption: Relations among Notions and Analysis of the Generic Composition Paradigm
Proceedings of ASIACRYPT 2000, Springer-Verlag, LNCS 1976, pp. 531-545
Blockwise-Adaptive Attackers Revisiting the (In)Security of Some Provably Secure Encryption Modes: CBC, GEM, IACBC
Advances in Cryptology — CRYPTO 2002. CRYPTO 2002. Lecture Notes in Computer Science, vol 2442. Springer, Berlin, Heidelberg
Authenticated On-Line Encryption
Selected Areas in Cryptography. SAC 2003. Lecture Notes in Computer Science, vol 3006. Springer, Berlin, Heidelberg.
Authenticated and Misuse-Resistant Encryption of Key-Dependent Data
Advances in Cryptology – CRYPTO 2011. CRYPTO 2011. Lecture Notes in Computer Science, vol 6841. Springer, Berlin, Heidelberg.
Authenticated and Misuse-Resistant Encryption of Key-Dependent DataSecurity of Symmetric Primitives under Incorrect Usage of Keys
IACR Transactions on Symmetric Cryptology, 2017(1), 449–473.
Partitioning Oracle Attacks
30th USENIX Security Symposium (USENIX Security 21), 195--212
Message Franking via Committing Authenticated Encryption.
Advances in Cryptology – CRYPTO 2017. CRYPTO 2017. Lecture Notes in Computer Science, vol 10403. Springer, Cham
Mode-Level vs. Implementation-Level Physical Security in Symmetric Cryptography: A Practical Guide Through the Leakage-Resistance Jungle
Advances in Cryptology – CRYPTO 2020. CRYPTO 2020. Lecture Notes in Computer Science, vol 12170. Springer, Cham
Authenticated Encryption with Nonce Misuse and Physical Leakages: Definitions, Separation Results and Leveled Constructions
Progress in Cryptology – LATINCRYPT 2019. LATINCRYPT 2019. Lecture Notes in Computer Science, vol 11774. Springer, Cham
The Multi-User Security of Authenticated Encryption: AES-GCM in TLS 1.3
Advances in Cryptology – CRYPTO 2016. CRYPTO 2016. Lecture Notes in Computer Science, vol 9814. Springer, Berlin, Heidelberg
A Provable-Security Treatment of the Key-Wrap Problem
Advances in Cryptology - EUROCRYPT 2006. EUROCRYPT 2006. Lecture Notes in Computer Science, vol 4004. Springer, Berlin, Heidelberg
Boosting Authenticated Encryption Robustness with Minimal Modifications
Advances in Cryptology – CRYPTO 2017. CRYPTO 2017. Lecture Notes in Computer Science, vol 10403. Springer, Cham
Reforgeability of Authenticated Encryption Schemes
Information Security and Privacy. ACISP 2017. Lecture Notes in Computer Science, vol 10343. Springer, Cham
MAC Reforgeability
Fast Software Encryption. FSE 2009. Lecture Notes in Computer Science, vol 5665. Springer, Berlin, Heidelberg
How to Securely Release Unverified Plaintext in Authenticated Encryption
Advances in Cryptology – ASIACRYPT 2014. ASIACRYPT 2014. Lecture Notes in Computer Science, vol 8873. Springer, Berlin, Heidelberg
Report on Lightweight Cryptography
Online Authenticated-Encryption and its Nonce-Reuse Misuse-Resistance
Advances in Cryptology -- CRYPTO 2015. CRYPTO 2015. Lecture Notes in Computer Science, vol 9215. Springer, Berlin, Heidelberg
INT-RUP Secure Lightweight Parallel AE Modes
IACR Transactions on Symmetric Cryptology, 2019(4), 81–118
CIMINION: Symmetric Encryption Based on Toffoli-Gates over Large Finite Fields
Advances in Cryptology – EUROCRYPT 2021. EUROCRYPT 2021. Lecture Notes in Computer Science(), vol 12697. Springer, Cham
Incremental Unforgeable Encryption
Fast Software Encryption. FSE 2001. Lecture Notes in Computer Science, vol 2355. Springer, Berlin, Heidelberg
A New Mode of Operation for Incremental Authenticated Encryption with Associated Data
Selected Areas in Cryptography – SAC 2015. SAC 2015. Lecture Notes in Computer Science(), vol 9566. Springer, Cham
Nonces Are Noticed: AEAD Revisited
Advances in Cryptology – CRYPTO 2019. CRYPTO 2019. Lecture Notes in Computer Science, vol 11692. Springer, Cham
A formal treatment of remotely keyed encryption
Advances in Cryptology — EUROCRYPT'98. EUROCRYPT 1998. Lecture Notes in Computer Science, vol 1403. Springer, Berlin, Heidelberg
Concealment and Its Applications to Authenticated Encryption
Advances in Cryptology — EUROCRYPT 2003. EUROCRYPT 2003. Lecture Notes in Computer Science, vol 2656. Springer, Berlin, Heidelberg
Robust Authenticated-Encryption AEZ and the Problem That It Solves
Advances in Cryptology -- EUROCRYPT 2015. EUROCRYPT 2015. Lecture Notes in Computer Science(), vol 9056. Springer, Berlin, Heidelberg.