rfc9771v1.txt   rfc9771.txt 
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* A deterministic operation of authenticated decryption has four * A deterministic operation of authenticated decryption has four
inputs, each a binary string: a secret key K of a fixed bit inputs, each a binary string: a secret key K of a fixed bit
length, a nonce N, associated data A, and a ciphertext C. The length, a nonce N, associated data A, and a ciphertext C. The
operation verifies the integrity of the ciphertext and operation verifies the integrity of the ciphertext and
associated data and decrypts the ciphertext. It returns a associated data and decrypts the ciphertext. It returns a
special symbol FAIL if the inputs are not authentic; otherwise, special symbol FAIL if the inputs are not authentic; otherwise,
the operation returns a plaintext P. the operation returns a plaintext P.
We note that specifications of AEAD algorithms that use We note that specifications of AEAD algorithms that use
authentication tags to ensure integrity MAY define it as an authentication tags to ensure integrity may define the authentication
independent output of the encryption operation and as an independent tag as an independent output of the encryption operation and an
input of the decryption operation. Throughout this document, by independent input of the decryption operation. Throughout this
default, we consider the authentication tag as part of the document, by default, we consider the authentication tag as part of
ciphertext. the ciphertext.
For more details on the AEAD definition, please refer to [RFC5116]. For more details on the AEAD definition, please refer to [RFC5116].
Throughout this document, by default, we consider nonce-based AEAD Throughout this document, by default, we consider nonce-based AEAD
algorithms, which have an interface as defined above, and we give no algorithms, which have an interface as defined above, and we give no
other restrictions on their structure. However, some properties other restrictions on their structure. However, some properties
considered in the document apply only to particular classes of such considered in the document apply only to particular classes of such
algorithms, like AEAD algorithms based on block ciphers (such algorithms, like AEAD algorithms based on block ciphers (such
algorithms use a block cipher as a building block). If that is the algorithms use a block cipher as a building block). If that is the
case, we explicitly point that out in the corresponding section. case, we explicitly point that out in the corresponding section.
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We say that an AEAD algorithm provides security if it provides the We say that an AEAD algorithm provides security if it provides the
conventional properties listed in this section. conventional properties listed in this section.
4.2.1. Confidentiality 4.2.1. Confidentiality
Definition: Definition:
An AEAD algorithm guarantees that the plaintext is not available An AEAD algorithm guarantees that the plaintext is not available
to an active, nonce-respecting adversary. to an active, nonce-respecting adversary.
Security notion: Security notions:
IND-CCA [BN2000] (or IND-CCA2 [S04]) IND-CCA [BN08] (or IND-CCA2 [S04])
Synonyms: Synonyms:
Message privacy Message privacy
Notes: Notes:
Confidentiality against passive adversaries can also be Confidentiality against passive adversaries can also be
considered. The corresponding security notion is IND-CPA [BN2000] considered. The corresponding security notion is IND-CPA [BN08]
[R02]. [R02].
Further reading: Further reading:
[R02], [BN2000], [S04] [R02], [BN08], [S04]
4.2.2. Data Integrity 4.2.2. Data Integrity
Definition: Definition:
An AEAD algorithm allows one to ensure that the ciphertext and the An AEAD algorithm allows one to ensure that the ciphertext and the
associated data have not been changed or forged by an active, associated data have not been changed or forged by an active,
nonce-respecting adversary. nonce-respecting adversary.
Security notion: Security notions:
IND-CTXT [BN2000] (or AUTH [R02]) INT-CTXT [BN08] (or AUTH [R02])
Synonyms: Synonyms:
Message authentication, authenticity Message authentication, authenticity
Further reading: Further reading:
[R02], [BN2000], [S04] [R02], [BN08], [S04]
4.2.3. Authenticated Encryption Security 4.2.3. Authenticated Encryption Security
Definition: Definition:
An AEAD algorithm provides confidentiality and data integrity An AEAD algorithm provides confidentiality and data integrity
against active, nonce-respecting adversaries. against active, nonce-respecting adversaries.
Security notion: Security notions:
IND-CPA and IND-CTXT [BN2000] [R02] (or equivalently, IND-CCA3 IND-CPA and INT-CTXT [BN08] [R02] (or equivalently, IND-CCA3
[S04]) [S04])
Notes: Notes:
Please refer to [AEAD-LIMITS] for usage limits on modern AEAD Please refer to [AEAD-LIMITS] for usage limits on modern AEAD
algorithms used in IETF protocols. algorithms used in IETF protocols.
Further reading: Further reading:
[R02], [BN2000], [S04] [R02], [BN08], [S04]
4.3. Security Properties 4.3. Security Properties
4.3.1. Blockwise Security 4.3.1. Blockwise Security
Definition: Definition:
An AEAD algorithm provides security even if an adversary can An AEAD algorithm provides security even if an adversary can
adaptively choose the next part of the plaintext depending on adaptively choose the next part of the plaintext depending on
already-computed ciphertext parts during an encryption operation. already-computed ciphertext parts during an encryption operation.
Security notion: Security notions:
D-LORS-BCPA for confidentiality against passive adversaries, B- D-LORS-BCPA for confidentiality against passive adversaries, B-
INT-CTXT for integrity [EV17]; OAE1 [HRRV15] (a stronger notion; INT-CTXT for integrity [EV17]; OAE1 [HRRV15] (a stronger notion;
originally OAE (Online Authenticated Encryption) in [FFL12]) originally OAE (Online Authenticated Encryption) in [FFL12])
Examples: Examples:
Deoxys [JNPS21], SAEF [ABV21] Deoxys [JNPS21], SAEF [ABV21]
Notes: Notes:
Blockwise security is highly relevant for streamable AEAD Blockwise security is highly relevant for streamable AEAD
algorithms (see Section 4.4.8). The OAE1 security notion [HRRV15] algorithms (see Section 4.4.8). The OAE1 security notion [HRRV15]
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4.3.2. Full Commitment 4.3.2. Full Commitment
Definition: Definition:
An AEAD algorithm guarantees that it is hard to find two or more An AEAD algorithm guarantees that it is hard to find two or more
different tuples of the key, nonce, associated data, and plaintext different tuples of the key, nonce, associated data, and plaintext
such that they encrypt to the same ciphertext. In other words, an such that they encrypt to the same ciphertext. In other words, an
AEAD scheme guarantees that a ciphertext is a commitment to all AEAD scheme guarantees that a ciphertext is a commitment to all
inputs of an authenticated encryption operation. inputs of an authenticated encryption operation.
Security notion: Security notions:
CMT-4 [BH22], generalized CMT for a restricted setting (see the CMT-4 [BH22], generalized CMT for a restricted setting (see the
notes below) [MLGR23] notes below) [MLGR23]
Examples: Examples:
Ascon [DEMS21a] [DEMS21b] [YSS23], full committing versions of Ascon [DEMS21a] [DEMS21b] [YSS23], full committing versions of
Galois/Counter Mode (GCM) and GCM-SIV [BH22], generic Galois/Counter Mode (GCM) and GCM-SIV [BH22], generic
constructions [BH22] and [CR22] constructions [BH22] and [CR22]
Notes: Notes:
Full commitment can be considered in a weaker setting, where Full commitment can be considered in a weaker setting, where
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4.3.3. Key Commitment 4.3.3. Key Commitment
Definition: Definition:
An AEAD algorithm guarantees that it is hard to find two or more An AEAD algorithm guarantees that it is hard to find two or more
different keys and the same number of potentially equal triples of different keys and the same number of potentially equal triples of
nonce, associated data, and plaintext such that they encrypt to nonce, associated data, and plaintext such that they encrypt to
the same ciphertext under corresponding keys. In other words, an the same ciphertext under corresponding keys. In other words, an
AEAD scheme guarantees that a ciphertext is a commitment to the AEAD scheme guarantees that a ciphertext is a commitment to the
key used for an authenticated encryption operation. key used for an authenticated encryption operation.
Security notion: Security notions:
CMT-1 [BH22] CMT-1 [BH22]
Synonyms: Synonyms:
Key robustness, key collision resistance Key robustness, key collision resistance
Examples: Examples:
Ascon [DEMS21a] [DEMS21b] [YSS23], generic constructions from Ascon [DEMS21a] [DEMS21b] [YSS23], generic constructions from
[BH22] and [CR22] [BH22] and [CR22]
Notes: Notes:
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Further reading: Further reading:
[BH22], [CR22], [FOR17], [LGR21], [GLR17] [BH22], [CR22], [FOR17], [LGR21], [GLR17]
4.3.4. Leakage Resistance 4.3.4. Leakage Resistance
Definition: Definition:
An AEAD algorithm provides security even if some additional An AEAD algorithm provides security even if some additional
information about computations of an encryption (and possibly information about computations of an encryption (and possibly
decryption) operation is obtained via side-channel leakages. decryption) operation is obtained via side-channel leakages.
Security notion: Security notions:
CIL1 [GPPS19] (CIML2 [BPPS17] with leakages in decryption) for CIL1 [GPPS19] (CIML2 [BPPS17] with leakages in decryption) for
integrity, CCAL1 [GPPS19] (CCAmL2 [GPPS19] with leakages in integrity, CCAL1 [GPPS19] (CCAmL2 [GPPS19] with leakages in
decryption) for authenticated encryption security decryption) for authenticated encryption security
Examples: Examples:
Ascon [DEMS21a] [DEMS21b] (security under CIML2 and CCAL1 notions Ascon [DEMS21a] [DEMS21b] (security under CIML2 and CCAL1 notions
[B20]), TEDT [GPPS19] [B20]), TEDT [GPPS19]
Notes: Notes:
Leakages during AEAD operation executions are implementation- Leakages during AEAD operation executions are implementation-
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Further reading: Further reading:
[GPPS19], [B20], [BPPS17], [BMOS17] [GPPS19], [B20], [BPPS17], [BMOS17]
4.3.5. Multi-user Security 4.3.5. Multi-user Security
Definition: Definition:
The security of an AEAD algorithm degrades slower than linearly The security of an AEAD algorithm degrades slower than linearly
with an increase in the number of users. with an increase in the number of users.
Security notion: Security notions:
mu-ind [BT16] mu-ind [BT16]
Examples: Examples:
AES-GCM [D07], ChaCha20-Poly1305 [RFC8439], AES-GCM-SIV [RFC8452], AES-GCM [D07], ChaCha20-Poly1305 [RFC8439], AES-GCM-SIV [RFC8452],
AEGIS [AEGIS-AEAD] AEGIS [AEGIS-AEAD]
Notes: Notes:
It holds that for any AEAD algorithm, security degrades no worse For any AEAD algorithm, security degrades no worse than linearly
than linearly with an increase in the number of users [BT16]. with an increase in the number of users [BT16]. However, for some
However, for some applications with a significant number of users, applications with a significant number of users, better multi-user
better multi-user guarantees are required. For example, in the guarantees are required. For example, in the TLS 1.3 protocol,
TLS 1.3 protocol, AEAD algorithms are used with a randomized nonce AEAD algorithms are used with a randomized nonce
(deterministically derived from a traffic secret and a sequence (deterministically derived from a traffic secret and a sequence
number) to address this issue. Using nonce randomization in block number) to address this issue. Using nonce randomization in block
cipher counter-based AEAD modes can contribute to multi-user cipher counter-based AEAD modes can contribute to multi-user
security [BT16]. Multi-user usage limits for AES-GCM and security [BT16]. Multi-user usage limits for AES-GCM and
ChaCha20-Poly1305 are provided in [AEAD-LIMITS]. ChaCha20-Poly1305 are provided in [AEAD-LIMITS].
A weaker security notion, multi-user key recovery, is also A weaker security notion, multi-user key recovery, is also
introduced and thoroughly studied in [BT16]. While this document introduced and thoroughly studied in [BT16]. While this document
focuses on indistinguishability for security notions, key recovery focuses on indistinguishability for security notions, key recovery
might be relevant and valuable to study alongside might be relevant and valuable to study alongside
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[BT16], [HTT18], [LMP17], [DGGP21], [BHT18] [BT16], [HTT18], [LMP17], [DGGP21], [BHT18]
4.3.6. Nonce Hiding 4.3.6. Nonce Hiding
Definition: Definition:
An AEAD algorithm provides confidentiality for the nonce value An AEAD algorithm provides confidentiality for the nonce value
used to encrypt plaintext. The algorithm includes information used to encrypt plaintext. The algorithm includes information
about the nonce in the ciphertext and doesn't require the nonce as about the nonce in the ciphertext and doesn't require the nonce as
input for the decryption operation. input for the decryption operation.
Security notion: Security notions:
AE2 [BNT19] AE2 [BNT19]
Examples: Examples:
Hide-Nonce (HN) transforms [BNT19] Hide-Nonce (HN) transforms [BNT19]
Notes: Notes:
As discussed in [BNT19], adversary-visible nonces might compromise As discussed in [BNT19], adversary-visible nonces might compromise
message and user privacy, similar to the way any metadata might. message and user privacy, similar to the way any metadata might.
As pointed out in [B13], even using a counter as a nonce value As pointed out in [B13], even using a counter as a nonce value
might compromise privacy. Designing a privacy-preserving way to might compromise privacy. Designing a privacy-preserving way to
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Definition: Definition:
An AEAD algorithm provides security (resilience or resistance) An AEAD algorithm provides security (resilience or resistance)
even if an adversary can repeat nonces in its encryption queries. even if an adversary can repeat nonces in its encryption queries.
Nonce misuse resilience and resistance are defined as follows: Nonce misuse resilience and resistance are defined as follows:
Nonce misuse resilience: Security is provided for messages Nonce misuse resilience: Security is provided for messages
encrypted with non-repeated (fresh) nonces (correctly encrypted encrypted with non-repeated (fresh) nonces (correctly encrypted
messages). messages).
Security notion: Security notions:
CPA resilience (confidentiality), authenticity resilience Chosen-Plaintext Attack (CPA) resilience (confidentiality),
(integrity), CCA resilience (authenticated encryption) authenticity resilience (integrity), Chosen-Ciphertext
[ADL17] Attack (CCA) resilience (authenticated encryption) [ADL17]
Examples: Examples:
ChaCha20-Poly1305 [RFC8439], AES-GCM [D07] (only ChaCha20-Poly1305 [RFC8439], AES-GCM [D07] (only
confidentiality) confidentiality)
Nonce misuse resistance: Security is provided for all messages Nonce misuse resistance: Security is provided for all messages
that were not encrypted with the same nonce value more than that were not encrypted with the same nonce value more than
once. once.
Security notion: Security notions:
MRAE [RS06] MRAE [RS06]
Examples: Examples:
AES-GCM-SIV [RFC8452], Deoxys-II [JNPS21] AES-GCM-SIV [RFC8452], Deoxys-II [JNPS21]
Notes: Notes:
Synthetic Initialization Vector (SIV) construction [RS06] is Synthetic Initialization Vector (SIV) construction [RS06] is
a generic construction that provides nonce misuse a generic construction that provides nonce misuse
resistance. resistance.
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Nonce misuse resilience follows from nonce misuse resistance. Nonce misuse resilience follows from nonce misuse resistance.
Nonce misuse resistance does not follow from nonce misuse Nonce misuse resistance does not follow from nonce misuse
resilience. resilience.
Applications: Applications:
Any application where nonce uniqueness can't be guaranteed, Any application where nonce uniqueness can't be guaranteed,
security against fault-injection attacks and malfunctions, security against fault-injection attacks and malfunctions,
processes parallelization, full disk encryption processes parallelization, full disk encryption
Further reading: Further reading:
[RS06], [ADL17] [RS06], [ADL17], [IIM25]
4.3.8. Quantum Security 4.3.8. Quantum Security
Definition: Definition:
An AEAD algorithm provides security (in a Q1 or Q2 model) against An AEAD algorithm provides security (in a Q1 or Q2 model) against
a quantum adversary. Q1 and Q2 models are defined as follows: a quantum adversary. Q1 and Q2 models are defined as follows:
Q1 model: An adversary has access to local quantum computational Q1 model: An adversary has access to local quantum computational
power. It has classical access to encryption and decryption power. It has classical access to encryption and decryption
oracles. oracles.
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Further reading: Further reading:
[KLLNP16], [BBCLNSS21], [G17] [KLLNP16], [BBCLNSS21], [G17]
4.3.9. Reforgeability Resilience 4.3.9. Reforgeability Resilience
Definition: Definition:
An AEAD algorithm guarantees that once a successful forgery for An AEAD algorithm guarantees that once a successful forgery for
the algorithm has been found, it is still hard to find any the algorithm has been found, it is still hard to find any
subsequent forgery. subsequent forgery.
Security notion: Security notions:
j-Int-CTXT [FLLW17] j-Int-CTXT [FLLW17]
Examples: Examples:
Deoxys [JNPS21], AEGIS [AEGIS-AEAD], Ascon [DEMS21a] [DEMS21b] Deoxys [JNPS21], AEGIS [AEGIS-AEAD], Ascon [DEMS21a] [DEMS21b]
Applications: Applications:
Voice over IP (VoIP), real-time streaming in a lightweight Voice over IP (VoIP), real-time streaming in a lightweight
setting, applications that require small ciphertext expansion setting, applications that require small ciphertext expansion
(i.e., short tags) (i.e., short tags)
Further reading: Further reading:
[BC09], [FLLW17] [BC09], [FLLW17]
4.3.10. Release of Unverified Plaintext (RUP) Integrity 4.3.10. Release of Unverified Plaintext (RUP) Integrity
Definition: Definition:
An AEAD algorithm provides data integrity even if plaintext is An AEAD algorithm provides data integrity even if plaintext is
released for every ciphertext, including those with failed released for every ciphertext, including those with failed
integrity verification. integrity verification.
Security notion: Security notions:
INT-RUP [A14] INT-RUP [A14]
Examples: Examples:
GCM-RUP [ADL17] GCM [IIM25], GCM-RUP [ADL17]
Applications: Applications:
Decryption with limited memory [FJMV2004], real-time streaming Decryption with limited memory [FJMV2004], real-time streaming
protocols protocols
Notes: Notes:
In [ADL17], a generic approach to achieve INT-RUP security is In [ADL17], a generic approach to achieve INT-RUP security is
introduced. introduced.
In the provided definition, we only consider integrity in the RUP In the provided definition, we only consider integrity in the RUP
setting, since confidentiality, in the usual sense, is setting, since confidentiality, in the usual sense, is
unachievable under RUP. In [A14], the notion of "Plaintext unachievable under RUP. In [A14], the notion of "Plaintext
Awareness" is introduced, capturing the best possible Awareness" is introduced, capturing the best possible
confidentiality under RUP in the following sense: "the adversary confidentiality under RUP in the following sense: "the adversary
cannot gain any additional knowledge about the plaintext from cannot gain any additional knowledge about the plaintext from
decryption queries besides what it can derive from encryption decryption queries besides what it can derive from encryption
queries". queries".
Further reading: Further reading:
[A14], [ADL17] [A14], [ADL17], [IIM25]
4.4. Implementation Properties 4.4. Implementation Properties
4.4.1. Hardware Efficient 4.4.1. Hardware Efficient
Definition: Definition:
An AEAD algorithm ensures optimal performance when operating on An AEAD algorithm ensures optimal performance when operating on
hardware that complies with the specified requirements. hardware that complies with the specified requirements.
Notes: Notes:
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requirements for the AEAD to fulfill its intended purpose, as well requirements for the AEAD to fulfill its intended purpose, as well
as to match its performance and security claims. as to match its performance and security claims.
4.4.2. Inverse-Free 4.4.2. Inverse-Free
Definition: Definition:
An AEAD algorithm based on a given primitive can be implemented An AEAD algorithm based on a given primitive can be implemented
without invoking the inverse of that primitive. without invoking the inverse of that primitive.
Examples: Examples:
AES-GCM [D07], ChaCha20-Poly1305 [RFC8439], OCB [RFC7253], MGM AES-GCM [D07], ChaCha20-Poly1305 [RFC8439], MGM [RFC9058], AEGIS
[RFC9058], AEGIS [AEGIS-AEAD] [AEGIS-AEAD]
Notes: Notes:
In a sponge-based AEAD algorithm, an underlying permutation is In a sponge-based AEAD algorithm, an underlying permutation is
viewed as a primitive. viewed as a primitive.
4.4.3. Lightweight 4.4.3. Lightweight
Definition: Definition:
An AEAD algorithm can be efficiently and securely implemented on An AEAD algorithm can be efficiently and securely implemented on
resource-constrained devices. In particular, it meets the resource-constrained devices. In particular, it meets the
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When specifying security requirements for an AEAD algorithm in an When specifying security requirements for an AEAD algorithm in an
application, it SHOULD be indicated, for every required security application, it SHOULD be indicated, for every required security
property, whether only integrity or confidentiality is necessary. property, whether only integrity or confidentiality is necessary.
Additionally, for each security property, it SHOULD be specified Additionally, for each security property, it SHOULD be specified
whether an analysis in an alternative security notion is required. whether an analysis in an alternative security notion is required.
We also note that some additional properties come with trade-offs in We also note that some additional properties come with trade-offs in
terms of classical security and efficiency, and they may only be terms of classical security and efficiency, and they may only be
supported in non-standardized or modified AEAD algorithms. This supported in non-standardized or modified AEAD algorithms. This
immediately implies challenges in deployment and interoperability. immediately implies challenges in deployment and interoperability.
In an application, the requirements for additional AEAD properties In an application, the requirements for additional AEAD properties
SHOULD be highly motivated and justified, as should all trade-offs be SHOULD be highly motivated and justified, and all trade-offs should
carefully considered. be carefully considered.
6. IANA Considerations 6. IANA Considerations
This document has no IANA actions. This document has no IANA actions.
7. References 7. References
7.1. Normative References 7.1. Normative References
[D07] Dworkin, M., "Recommendation for Block Cipher Modes of [D07] Dworkin, M., "Recommendation for Block Cipher Modes of
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187-220, DOI 10.1007/978-3-319-96884-1_7, 2018, 187-220, DOI 10.1007/978-3-319-96884-1_7, 2018,
<https://doi.org/10.1007/978-3-319-96884-1_7>. <https://doi.org/10.1007/978-3-319-96884-1_7>.
[BMOS17] Barwell, G., Martin, D.P., Oswald, E., and M. Stam, [BMOS17] Barwell, G., Martin, D.P., Oswald, E., and M. Stam,
"Authenticated Encryption in the Face of Protocol and Side "Authenticated Encryption in the Face of Protocol and Side
Channel Leakage", Advances in Cryptology - ASIACRYPT 2017, Channel Leakage", Advances in Cryptology - ASIACRYPT 2017,
Lecture Notes in Computer Science, vol. 10624, pp. Lecture Notes in Computer Science, vol. 10624, pp.
693-723, DOI 10.1007/978-3-319-70694-8_24, 2017, 693-723, DOI 10.1007/978-3-319-70694-8_24, 2017,
<https://doi.org/10.1007/978-3-319-70694-8_24>. <https://doi.org/10.1007/978-3-319-70694-8_24>.
[BN2000] Bellare, M. and C. Namprempre, "Authenticated Encryption: [BN08] Bellare, M. and C. Namprempre, "Authenticated Encryption:
Relations among Notions and Analysis of the Generic Relations among Notions and Analysis of the Generic
Composition Paradigm", Advances in Cryptology - ASIACRYPT Composition Paradigm", Journal of Cryptology, vol. 21, pp.
2000, Lecture Notes in Computer Science, vol. 1976, pp. 469-491, DOI 10.1007/s00145-008-9026-x, 2008,
531-545, DOI 10.1007/3-540-44448-3_41, 2000, <https://doi.org/10.1007/s00145-008-9026-x>.
<https://doi.org/10.1007/3-540-44448-3_41>.
[BNT19] Bellare, M., Ng, R., and B. Tackmann, "Nonces Are Noticed: [BNT19] Bellare, M., Ng, R., and B. Tackmann, "Nonces Are Noticed:
AEAD Revisited", Advances in Cryptology - CRYPTO 2019, AEAD Revisited", Advances in Cryptology - CRYPTO 2019,
Lecture Notes in Computer Science, vol. 11692, pp. Lecture Notes in Computer Science, vol. 11692, pp.
235-265, DOI 10.1007/978-3-030-26948-7_9, 2019, 235-265, DOI 10.1007/978-3-030-26948-7_9, 2019,
<https://doi.org/10.1007/978-3-030-26948-7_9>. <https://doi.org/10.1007/978-3-030-26948-7_9>.
[BPPS17] Berti, F., Pereira, O., Peters, T., and F.-X. Standaert, [BPPS17] Berti, F., Pereira, O., Peters, T., and F.-X. Standaert,
"On Leakage-Resilient Authenticated Encryption with "On Leakage-Resilient Authenticated Encryption with
Decryption Leakages", IACR Transactions on Symmetric Decryption Leakages", IACR Transactions on Symmetric
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DOI 10.1007/978-3-662-47989-6_24, 2015, DOI 10.1007/978-3-662-47989-6_24, 2015,
<https://doi.org/10.1007/978-3-662-47989-6_24>. <https://doi.org/10.1007/978-3-662-47989-6_24>.
[HTT18] Hoang, V.T., Tessaro, S., and A. Thiruvengadam, "The [HTT18] Hoang, V.T., Tessaro, S., and A. Thiruvengadam, "The
Multi-user Security of GCM, Revisited: Tight Bounds for Multi-user Security of GCM, Revisited: Tight Bounds for
Nonce Randomization", Proceedings of the 2018 ACM SIGSAC Nonce Randomization", Proceedings of the 2018 ACM SIGSAC
Conference on Computer and Communications Security (CCS Conference on Computer and Communications Security (CCS
'18), pp. 1429-1440, DOI 10.1145/3243734.3243816, 2018, '18), pp. 1429-1440, DOI 10.1145/3243734.3243816, 2018,
<https://doi.org/10.1145/3243734.3243816>. <https://doi.org/10.1145/3243734.3243816>.
[IIM25] Inoue, A., Iwata, T., and K. Minematsu, "Comprehensive
Robustness Analysis of GCM, CCM, and OCB3", Topics in
Cryptology – CT-RSA 2025, Lecture Notes in Computer
Science, vol. 15598, DOI 10.1007/978-3-031-88661-4_4,
2025, <https://doi.org/10.1007/978-3-031-88661-4_4>.
[JMV2002] Joux, A., Martinet, G., and F. Valette, "Blockwise- [JMV2002] Joux, A., Martinet, G., and F. Valette, "Blockwise-
Adaptive Attackers Revisiting the (In)Security of Some Adaptive Attackers Revisiting the (In)Security of Some
Provably Secure Encryption Modes: CBC, GEM, IACBC", Provably Secure Encryption Modes: CBC, GEM, IACBC",
Advances in Cryptology - CRYPTO 2002, Lecture Notes in Advances in Cryptology - CRYPTO 2002, Lecture Notes in
Computer Science, vol. 2442, DOI 10.1007/3-540-45708-9_2, Computer Science, vol. 2442, DOI 10.1007/3-540-45708-9_2,
2002, <https://doi.org/10.1007/3-540-45708-9_2>. 2002, <https://doi.org/10.1007/3-540-45708-9_2>.
[JNPS21] Jean, M., Nikolić, I., Peyrin, T., and Y. Seurin, "The [JNPS21] Jean, M., Nikolić, I., Peyrin, T., and Y. Seurin, "The
Deoxys AEAD family", Journal of Cryptology, vol. 34, no. Deoxys AEAD family", Journal of Cryptology, vol. 34, no.
31, DOI 10.1007/s00145-021-09397-w, 2021, 31, DOI 10.1007/s00145-021-09397-w, 2021,
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suffice. suffice.
For the examples given in this section, we leave it out of scope how For the examples given in this section, we leave it out of scope how
to concretely redefine conventional security for these classes; we to concretely redefine conventional security for these classes; we
only briefly describe the additional functionality they offer and only briefly describe the additional functionality they offer and
provide further references. provide further references.
A.1. Incremental Authenticated Encryption A.1. Incremental Authenticated Encryption
Definition: Definition:
An AEAD algorithm allows re-encrypting and authenticating a For a message that only partly differs from some previous message,
message (associated data and a plaintext pair), which only partly an AEAD algorithm allows re-encrypting and authenticating that
differs from some previous message, faster than processing it from message (associated data and a plaintext pair) faster than
scratch. processing it from scratch.
Examples: Examples:
Incremental AEAD algorithm of [SY16] Incremental AEAD algorithm of [SY16]
Security notion: Security notions:
Privacy, authenticity [SY16] Privacy, authenticity [SY16]
Notes: Notes:
When compared with conventional AEAD, the interface of an When compared with conventional AEAD, the interface of an
incremental AEAD algorithm is usually expanded with several incremental AEAD algorithm is usually expanded with several
operations, which perform different types of updates. For operations, which perform different types of updates. For
example, one can consider operations such as "Append" or "Chop", example, one can consider operations such as "Append" or "Chop",
which provide a straightforward additional functionality. A which provide a straightforward additional functionality. A
comprehensive definition of an incremental AEAD interface is comprehensive definition of an incremental AEAD interface is
provided in [SY16]. provided in [SY16].
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expansion (the difference between the length of plaintext and expansion (the difference between the length of plaintext and
corresponding ciphertext) along with an input to the encryption corresponding ciphertext) along with an input to the encryption
operation. This feature enables the regulation of desired data operation. This feature enables the regulation of desired data
integrity guarantees, which depend on ciphertext expansion, for integrity guarantees, which depend on ciphertext expansion, for
each particular application while using the same algorithm each particular application while using the same algorithm
implementation. implementation.
Examples: Examples:
AEZ [HKR2015] AEZ [HKR2015]
Security notion: Security notions:
RAE [HKR2015] Robust Authenticated Encryption (RAE) [HKR2015]
Notes: Notes:
The security goal of robust AEAD algorithms is to ensure the best The security goal of robust AEAD algorithms is to ensure the best
possible security, even with small ciphertext expansion (referred possible security, even with small ciphertext expansion (referred
to as stretch). For instance, analyzing any AEAD algorithm with a to as stretch). For instance, analyzing any AEAD algorithm with a
one-byte stretch for conventional integrity reveals insecurity, as one-byte stretch for conventional integrity reveals insecurity, as
the probability of forging a ciphertext is no less than 1/256. the probability of forging a ciphertext is no less than 1/256.
Nonetheless, from the robust AEAD perspective, an algorithm with Nonetheless, from the robust AEAD perspective, an algorithm with
such forgery probability for a one-byte ciphertext expansion is such forgery probability for a one-byte ciphertext expansion is
secure, representing the best achievable security in that secure, representing the best achievable security in that
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