Network Working Group F. Denis Internet-Draft Fastly Inc. Intended status: Informational F. E. R. Scotoni Expires: 6 February 2023 S. Lucas Individual Contributor 5 August 2022 The AEGIS family of authenticated encryption algorithms draft-irtf-cfrg-aegis-aead-00 Abstract This document describes AEGIS-128L and AEGIS-256, two AES-based authenticated encryption algorithms designed for high-performance applications. Discussion Venues This note is to be removed before publishing as an RFC. Source for this draft and an issue tracker can be found at https://github.com/jedisct1/draft-aegis-aead. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 6 February 2023. Copyright Notice Copyright (c) 2022 IETF Trust and the persons identified as the document authors. All rights reserved. Denis, et al. Expires 6 February 2023 [Page 1] Internet-Draft The AEGIS family of authenticated encryp August 2022 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions and Definitions . . . . . . . . . . . . . . . . . 4 3. The AEGIS-128L Algorithm . . . . . . . . . . . . . . . . . . 6 3.1. Authenticated Encryption . . . . . . . . . . . . . . . . 7 3.2. Authenticated Decryption . . . . . . . . . . . . . . . . 8 3.3. The Init Function . . . . . . . . . . . . . . . . . . . . 9 3.4. The Update Function . . . . . . . . . . . . . . . . . . . 10 3.5. The Enc Function . . . . . . . . . . . . . . . . . . . . 11 3.6. The Dec Function . . . . . . . . . . . . . . . . . . . . 12 3.7. The DecPartial Function . . . . . . . . . . . . . . . . . 12 3.8. The Finalize Function . . . . . . . . . . . . . . . . . . 13 4. The AEGIS-256 Algorithm . . . . . . . . . . . . . . . . . . . 13 4.1. Authenticated Encryption . . . . . . . . . . . . . . . . 14 4.2. Authenticated Decryption . . . . . . . . . . . . . . . . 15 4.3. The Init Function . . . . . . . . . . . . . . . . . . . . 16 4.4. The Update Function . . . . . . . . . . . . . . . . . . . 17 4.5. The Enc Function . . . . . . . . . . . . . . . . . . . . 18 4.6. The Dec Function . . . . . . . . . . . . . . . . . . . . 18 4.7. The DecPartial Function . . . . . . . . . . . . . . . . . 19 4.8. The Finalize Function . . . . . . . . . . . . . . . . . . 20 5. Encoding (ct, tag) Tuples . . . . . . . . . . . . . . . . . . 20 6. Security Considerations . . . . . . . . . . . . . . . . . . . 20 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 8.1. Normative References . . . . . . . . . . . . . . . . . . 21 8.2. Informative References . . . . . . . . . . . . . . . . . 22 Appendix A. Test Vectors . . . . . . . . . . . . . . . . . . . . 23 A.1. AESRound Test Vector . . . . . . . . . . . . . . . . . . 23 A.2. AEGIS-128L Test Vectors . . . . . . . . . . . . . . . . . 23 A.2.1. Update Test Vector . . . . . . . . . . . . . . . . . 23 A.2.2. Test Vector 1 . . . . . . . . . . . . . . . . . . . . 24 A.2.3. Test Vector 2 . . . . . . . . . . . . . . . . . . . . 24 A.2.4. Test Vector 3 . . . . . . . . . . . . . . . . . . . . 25 A.2.5. Test Vector 4 . . . . . . . . . . . . . . . . . . . . 25 A.2.6. Test Vector 5 . . . . . . . . . . . . . . . . . . . . 25 A.2.7. Test Vector 6 . . . . . . . . . . . . . . . . . . . . 26 A.2.8. Test Vector 7 . . . . . . . . . . . . . . . . . . . . 26 Denis, et al. Expires 6 February 2023 [Page 2] Internet-Draft The AEGIS family of authenticated encryp August 2022 A.2.9. Test Vector 8 . . . . . . . . . . . . . . . . . . . . 27 A.2.10. Test Vector 9 . . . . . . . . . . . . . . . . . . . . 27 A.3. AEGIS-256 Test Vectors . . . . . . . . . . . . . . . . . 27 A.3.1. Update Test Vector . . . . . . . . . . . . . . . . . 27 A.3.2. Test Vector 1 . . . . . . . . . . . . . . . . . . . . 28 A.3.3. Test Vector 2 . . . . . . . . . . . . . . . . . . . . 28 A.3.4. Test Vector 3 . . . . . . . . . . . . . . . . . . . . 28 A.3.5. Test Vector 4 . . . . . . . . . . . . . . . . . . . . 29 A.3.6. Test Vector 5 . . . . . . . . . . . . . . . . . . . . 29 A.3.7. Test Vector 6 . . . . . . . . . . . . . . . . . . . . 30 A.3.8. Test Vector 7 . . . . . . . . . . . . . . . . . . . . 30 A.3.9. Test Vector 8 . . . . . . . . . . . . . . . . . . . . 31 A.3.10. Test Vector 9 . . . . . . . . . . . . . . . . . . . . 31 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 31 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32 1. Introduction This document describes the AEGIS-128L and AEGIS-256 authenticated encryption with associated data (AEAD) algorithms [AEGIS], which were chosen as additional finalists for high-performance applications in the Competition for Authenticated Encryption: Security, Applicability, and Robustness (CAESAR). Whilst AEGIS-128 was selected as a winner for this use case, AEGIS-128L has a better security margin alongside improved performance and AEGIS-256 uses a 256-bit key [LIMS21]. All variants of AEGIS are constructed from the AES encryption round function [FIPS-AES]. This document specifies: * AEGIS-128L, which has a 128-bit key, a 128-bit nonce, a 1024-bit state, a 128-bit authentication tag, and processes 256-bit input blocks. * AEGIS-256, which has a 256-bit key, a 256-bit nonce, a 768-bit state, a 128-bit authentication tag, and processes 128-bit input blocks. The AEGIS cipher family offers performance that significantly exceeds that of AES-GCM with hardware support for parallelizable AES block encryption [AEGIS]. Similarly, software implementations can also be faster, although to a lesser extent. Unlike with AES-GCM, nonces can be safely chosen at random with no practical limit when using AEGIS-256. AEGIS-128L also allows for more messages to be safely encrypted when using random nonces. With some existing AEAD schemes, such as AES-GCM, an attacker can generate a ciphertext that successfully decrypts under multiple different keys (a partitioning oracle attack) [LGR21]. This ability Denis, et al. Expires 6 February 2023 [Page 3] Internet-Draft The AEGIS family of authenticated encryp August 2022 to craft a (ciphertext, authentication tag) pair that verifies under multiple keys significantly reduces the number of required interactions with the oracle in order to perform an exhaustive search, making it practical if the key space is small. For example, with password-based encryption, an attacker can guess a large number of passwords at a time by recursively submitting such a ciphertext to an oracle, which speeds up a password search by reducing it to a binary search. A key-committing AEAD scheme is more resistant against partitioning oracle attacks than non-committing AEAD schemes, making it significantly harder to find multiple keys that are valid for a given authentication tag. As of the time of writing, no research has been published claiming that AEGIS is not a key-committing AEAD scheme. Finally, unlike most other AES-based AEAD constructions, such as Rocca and Tiaoxin, leaking the state does not leak the key. Note that an earlier version of Hongjun Wu and Bart Preneel's paper introducing AEGIS specified AEGIS-128L and AEGIS-256 sporting differences with regards to the computation of the authentication tag and the number of rounds in Finalize() respectively. We follow the specification of [AEGIS] that is current at the time of writing, which can be found in the References section of this document. 2. Conventions and Definitions 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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. Primitives: * |x|: the length of x in bits. * a ^ b: the bitwise exclusive OR operation between a and b. * a & b: the bitwise AND operation between a and b. * a || b: the concatenation of a and b. * a mod b: the remainder of the Euclidean division between a as the dividend and b as the divisor. * LE64(x): the little-endian encoding of 64-bit integer x. Denis, et al. Expires 6 February 2023 [Page 4] Internet-Draft The AEGIS family of authenticated encryp August 2022 * ZeroPad(x, n): padding operation. Trailing zeros are concatenated to x until the total length is a multiple of n bits. * Truncate(x, n): truncation operation. The first n bits of x are kept. * Split(x, n): splitting operation. x is split into n-bit blocks, ignoring partial blocks. * Tail(x, n): returns the last n bits of x. * AESRound(in, rk): a single round of the AES encryption round function, which is the composition of the SubBytes, ShiftRows, MixColums and AddRoundKey transformations, as defined in section 5 of [FIPS-AES]. Here, in is the 128-bit AES input state, and rk is the 128-bit round key. * Repeat(n, F): n sequential evaluations of the function F. * CtEq(a, b): compares a and b in constant-time, returning True for an exact match, False otherwise. AEGIS internal functions: * Update(M0, M1): the state update function. * Init(key, nonce): the initialization function. * Enc(xi): the input block encryption function. * Dec(ci): the input block decryption function. * DecPartial(cn): the input block decryption function for the last ciphertext bits when they do not fill an entire block. * Finalize(ad_len, msg_len): the authentication tag generation function. Input blocks are 256 bits for AEGIS-128L and 128 bits for AEGIS-256. AES blocks: * Si: the i-th AES block of the current state. * S'i: the i-th AES block of the next state. * {Si, ...Sj}: the vector of the i-th AES block of the current state to the j-th block of the current state. Denis, et al. Expires 6 February 2023 [Page 5] Internet-Draft The AEGIS family of authenticated encryp August 2022 * C0: the constant 0x000101020305080d1522375990e97962 as an AES block. * C1: the constant 0xdb3d18556dc22ff12011314273b528dd as an AES block. AES blocks are always 128 bits in length. Input and output values: * key: the encryption key (128 bits for AEGIS-128L, 256 bits for AEGIS-256). * nonce: the public nonce (128 bits for AEGIS-128L, 256 bits for AEGIS-256). * ad: the associated data. * msg: the plaintext. * ct: the ciphertext. * tag: the authentication tag (128 bits). 3. The AEGIS-128L Algorithm AEGIS-128L has a 1024-bit state, made of eight 128-bit blocks {S0, ...S7}. The parameters for this algorithm, whose meaning is defined in [RFC5116], Section 4 are: * K_LEN (key length) is 16 octets (128 bits). * P_MAX (maximum length of the plaintext) is 2^61 octets (2^64 bits). * A_MAX (maximum length of the associated data) is 2^61 octets (2^64 bits). * N_MIN (minimum nonce length) = N_MAX (maximum nonce length) = 16 octets (128 bits). * C_MAX (maximum ciphertext length) = P_MAX + tag length = 2^61 + 16 octets (2^64 + 128 bits). Denis, et al. Expires 6 February 2023 [Page 6] Internet-Draft The AEGIS family of authenticated encryp August 2022 Distinct associated data inputs, as described in [RFC5116], Section 3 shall be unambiguously encoded as a single input. It is up to the application to create a structure in the associated data input if needed. 3.1. Authenticated Encryption Encrypt(msg, ad, key, nonce) The Encrypt function encrypts a message and returns the ciphertext along with an authentication tag that verifies the authenticity of the message and associated data, if provided. Security: * For a given key, the nonce MUST NOT be reused under any circumstances; doing so allows an attacker to recover the internal state. * The key MUST be randomly chosen from a uniform distribution. Inputs: * msg: the message to be encrypted (length MUST be less than P_MAX). * ad: the associated data to authenticate (length MUST be less than A_MAX). * key: the encryption key. * nonce: the public nonce. Outputs: * ct: the ciphertext. * tag: the authentication tag. Steps: Denis, et al. Expires 6 February 2023 [Page 7] Internet-Draft The AEGIS family of authenticated encryp August 2022 Init(key, nonce) ct = {} ad_blocks = Split(ZeroPad(ad, 256), 256) for xi in ad_blocks: Enc(xi) msg_blocks = Split(ZeroPad(msg, 256), 256) for xi in msg_blocks: ct = ct || Enc(xi) tag = Finalize(|ad|, |msg|) ct = Truncate(ct, |msg|) return ct and tag 3.2. Authenticated Decryption Decrypt(ct, tag, ad, key, nonce) The Decrypt function decrypts a ciphertext, verifies that the authentication tag is correct, and returns the message on success or an error if tag verification failed. Security: * If tag verification fails, the decrypted message and wrong message authentication tag MUST NOT be given as output. The decrypted message MUST be overwritten with zeros. * The comparison of the input tag with the expected_tag MUST be done in constant time. Inputs: * ct: the ciphertext to be decrypted (length MUST be less than C_MAX). * tag: the authentication tag. * ad: the associated data to authenticate (length MUST be less than A_MAX). * key: the encryption key. * nonce: the public nonce. Denis, et al. Expires 6 February 2023 [Page 8] Internet-Draft The AEGIS family of authenticated encryp August 2022 Outputs: * Either the decrypted message msg, or an error indicating that the authentication tag is invalid for the given inputs. Steps: Init(key, nonce) msg = {} ad_blocks = Split(ZeroPad(ad, 256), 256) for xi in ad_blocks: Enc(xi) ct_blocks = Split(ct, 256) cn = Tail(ct, |ct| mod 256) for ci in ct_blocks: msg = msg || Dec(ci) if cn is not empty: msg = msg || DecPartial(cn) expected_tag = Finalize(|ad|, |msg|) if CtEq(tag, expected_tag) is False: erase msg return "verification failed" error else: return msg 3.3. The Init Function Init(key, nonce) The Init function constructs the initial state {S0, ...S7} using the given key and nonce. Inputs: * key: the encryption key. * nonce: the nonce. Defines: * {S0, ...S7}: the initial state. Denis, et al. Expires 6 February 2023 [Page 9] Internet-Draft The AEGIS family of authenticated encryp August 2022 Steps: S0 = key ^ nonce S1 = C1 S2 = C0 S3 = C1 S4 = key ^ nonce S5 = key ^ C0 S6 = key ^ C1 S7 = key ^ C0 Repeat(10, Update(nonce, key)) 3.4. The Update Function Update(M0, M1) The Update function is the core of the AEGIS-128L algorithm. It updates the state {S0, ...S7} using two 128-bit values. Inputs: * M0: the first 128-bit block to be absorbed. * M1: the second 128-bit block to be absorbed. Modifies: * {S0, ...S7}: the state. Steps: Denis, et al. Expires 6 February 2023 [Page 10] Internet-Draft The AEGIS family of authenticated encryp August 2022 S'0 = AESRound(S7, S0 ^ M0) S'1 = AESRound(S0, S1) S'2 = AESRound(S1, S2) S'3 = AESRound(S2, S3) S'4 = AESRound(S3, S4 ^ M1) S'5 = AESRound(S4, S5) S'6 = AESRound(S5, S6) S'7 = AESRound(S6, S7) S0 = S'0 S1 = S'1 S2 = S'2 S3 = S'3 S4 = S'4 S5 = S'5 S6 = S'6 S7 = S'7 3.5. The Enc Function Enc(xi) The Enc function encrypts a 256-bit input block xi using the state {S0, ...S7}. Inputs: * xi: the 256-bit input block. Outputs: * ci: the 256-bit encrypted block. Steps: z0 = S6 ^ S1 ^ (S2 & S3) z1 = S2 ^ S5 ^ (S6 & S7) t0, t1 = Split(xi, 128) out0 = t0 ^ z0 out1 = t1 ^ z1 Update(t0, t1) ci = out0 || out1 return ci Denis, et al. Expires 6 February 2023 [Page 11] Internet-Draft The AEGIS family of authenticated encryp August 2022 3.6. The Dec Function Dec(ci) The Dec function decrypts a 256-bit input block ci using the state {S0, ...S7}. Inputs: * ci: the 256-bit encrypted block. Outputs: * xi: the 256-bit decrypted block. Steps: z0 = S6 ^ S1 ^ (S2 & S3) z1 = S2 ^ S5 ^ (S6 & S7) t0, t1 = Split(ci, 128) out0 = t0 ^ z0 out1 = t1 ^ z1 Update(out0, out1) xi = out0 || out1 return xi 3.7. The DecPartial Function DecPartial(cn) The DecPartial function decrypts the last ciphertext bits cn using the state {S0, ...S7} when they do not fill an entire block. Inputs: * cn: the encrypted input. Outputs: * xn: the decryption of cn. Steps: Denis, et al. Expires 6 February 2023 [Page 12] Internet-Draft The AEGIS family of authenticated encryp August 2022 z0 = S6 ^ S1 ^ (S2 & S3) z1 = S2 ^ S5 ^ (S6 & S7) t0, t1 = Split(ZeroPad(cn, 256), 128) out0 = t0 ^ z0 out1 = t1 ^ z1 xn = Truncate(out0 || out1, |cn|) v0, v1 = Split(ZeroPad(xn, 256), 128) Update(v0, v1) return xn 3.8. The Finalize Function Finalize(ad_len, msg_len) The Finalize function computes a 128-bit tag that authenticates the message and associated data. Inputs: * ad_len: the length of the associated data in bits. * msg_len: the length of the message in bits. Outputs: * tag: the authentication tag. Steps: t = S2 ^ (LE64(ad_len) || LE64(msg_len)) Repeat(7, Update(t, t)) tag = S0 ^ S1 ^ S2 ^ S3 ^ S4 ^ S5 ^ S6 return tag 4. The AEGIS-256 Algorithm AEGIS-256 has a 768-bit state, made of six 128-bit blocks {S0, ...S5}. The parameters for this algorithm, whose meaning is defined in [RFC5116], Section 4 are: Denis, et al. Expires 6 February 2023 [Page 13] Internet-Draft The AEGIS family of authenticated encryp August 2022 * K_LEN (key length) is 32 octets (256 bits). * P_MAX (maximum length of the plaintext) is 2^61 octets (2^64 bits). * A_MAX (maximum length of the associated data) is 2^61 octets (2^64 bits). * N_MIN (minimum nonce length) = N_MAX (maximum nonce length) = 32 octets (256 bits). * C_MAX (maximum ciphertext length) = P_MAX + tag length = 2^61 + 16 octets (2^64 + 128 bits). Distinct associated data inputs, as described in [RFC5116], Section 3 shall be unambiguously encoded as a single input. It is up to the application to create a structure in the associated data input if needed. 4.1. Authenticated Encryption Encrypt(msg, ad, key, nonce) The Encrypt function encrypts a message and returns the ciphertext along with an authentication tag that verifies the authenticity of the message and associated data, if provided. Security: * For a given key, the nonce MUST NOT be reused under any circumstances; doing so allows an attacker to recover the internal state. * The key MUST be randomly chosen from a uniform distribution. Inputs: * msg: the message to be encrypted (length MUST be less than P_MAX). * ad: the associated data to authenticate (length MUST be less than A_MAX). * key: the encryption key. * nonce: the public nonce. Outputs: Denis, et al. Expires 6 February 2023 [Page 14] Internet-Draft The AEGIS family of authenticated encryp August 2022 * ct: the ciphertext. * tag: the authentication tag. Steps: Init(key, nonce) ct = {} ad_blocks = Split(ZeroPad(ad, 128), 128) for xi in ad_blocks: Enc(xi) msg_blocks = Split(ZeroPad(msg, 128), 128) for xi in msg_blocks: ct = ct || Enc(xi) tag = Finalize(|ad|, |msg|) ct = Truncate(ct, |msg|) return ct and tag 4.2. Authenticated Decryption Decrypt(ct, tag, ad, key, nonce) The Decrypt function decrypts a ciphertext, verifies that the authentication tag is correct, and returns the message on success or an error if tag verification failed. Security: * If tag verification fails, the decrypted message and wrong message authentication tag MUST NOT be given as output. The decrypted message MUST be overwritten with zeros. * The comparison of the input tag with the expected_tag MUST be done in constant time. Inputs: * ct: the ciphertext to be decrypted (length MUST be less than C_MAX). * tag: the authentication tag. Denis, et al. Expires 6 February 2023 [Page 15] Internet-Draft The AEGIS family of authenticated encryp August 2022 * ad: the associated data to authenticate (length MUST be less than A_MAX). * key: the encryption key. * nonce: the public nonce. Outputs: * Either the decrypted message msg, or an error indicating that the authentication tag is invalid for the given inputs. Steps: Init(key, nonce) msg = {} ad_blocks = Split(ZeroPad(ad, 128), 128) for xi in ad_blocks: Enc(xi) ct_blocks = Split(ZeroPad(ct, 128), 128) cn = Tail(ct, |ct| mod 128) for ci in ct_blocks: msg = msg || Dec(ci) if cn is not empty: msg = msg || DecPartial(cn) expected_tag = Finalize(|ad|, |msg|) if CtEq(tag, expected_tag) is False: erase msg return "verification failed" error else: return msg 4.3. The Init Function Init(key, nonce) The Init function constructs the initial state {S0, ...S5} using the given key and nonce. Inputs: Denis, et al. Expires 6 February 2023 [Page 16] Internet-Draft The AEGIS family of authenticated encryp August 2022 * key: the encryption key. * nonce: the nonce. Defines: * {S0, ...S5}: the initial state. Steps: k0, k1 = Split(key, 128) n0, n1 = Split(nonce, 128) S0 = k0 ^ n0 S1 = k1 ^ n1 S2 = C1 S3 = C0 S4 = k0 ^ C0 S5 = k1 ^ C1 Repeat(4, Update(k0) Update(k1) Update(k0 ^ n0) Update(k1 ^ n1) ) 4.4. The Update Function Update(M) The Update function is the core of the AEGIS-256 algorithm. It updates the state {S0, ...S5} using a 128-bit value. Inputs: * msg: the block to be absorbed. Modifies: * {S0, ...S5}: the state. Steps: Denis, et al. Expires 6 February 2023 [Page 17] Internet-Draft The AEGIS family of authenticated encryp August 2022 S'0 = AESRound(S5, S0 ^ M) S'1 = AESRound(S0, S1) S'2 = AESRound(S1, S2) S'3 = AESRound(S2, S3) S'4 = AESRound(S3, S4) S'5 = AESRound(S4, S5) S0 = S'0 S1 = S'1 S2 = S'2 S3 = S'3 S4 = S'4 S5 = S'5 4.5. The Enc Function Enc(xi) The Enc function encrypts a 128-bit input block xi using the state {S0, ...S5}. Inputs: * xi: the input block. Outputs: * ci: the encrypted input block. Steps: z = S1 ^ S4 ^ S5 ^ (S2 & S3) Update(xi) ci = xi ^ z return ci 4.6. The Dec Function Dec(ci) The Dec function decrypts a 128-bit input block ci using the state {S0, ...S5}. Inputs: Denis, et al. Expires 6 February 2023 [Page 18] Internet-Draft The AEGIS family of authenticated encryp August 2022 * ci: the encrypted input block. Outputs: * xi: the decrypted block. Steps: z = S1 ^ S4 ^ S5 ^ (S2 & S3) xi = ci ^ z Update(xi) return xi It returns the 128-bit block out. 4.7. The DecPartial Function DecPartial(cn) The DecPartial function decrypts the last ciphertext bits cn using the state {S0, ...S5} when they do not fill an entire block. Inputs: * cn: the encrypted input. Outputs: * xn: the decryption of cn. Steps: z = S1 ^ S4 ^ S5 ^ (S2 & S3) t = ZeroPad(cn, 128) out = t ^ z xn = Truncate(out, |cn|) v = ZeroPad(xn, 128) Update(v) return xn Denis, et al. Expires 6 February 2023 [Page 19] Internet-Draft The AEGIS family of authenticated encryp August 2022 4.8. The Finalize Function Finalize(ad_len, msg_len) The Finalize function computes a 128-bit tag that authenticates the message and associated data. Inputs: * ad_len: the length of the associated data in bits. * msg_len: the length of the message in bits. Outputs: * tag: the authentication tag. Steps: t = S3 ^ (LE64(ad_len) || LE64(msg_len)) Repeat(7, Update(t)) tag = S0 ^ S1 ^ S2 ^ S3 ^ S4 ^ S5 return tag 5. Encoding (ct, tag) Tuples Applications MAY keep the ciphertext and the 128-bit authentication tag in distinct structures or encode both as a single string. In the latter case, the tag MUST immediately follow the ciphertext: combined_ct = ct || tag 6. Security Considerations AEGIS-256 offers 256-bit message security against plaintext and state recovery, whereas AEGIS-128L offers 128-bit security. Both have a 128-bit authentication tag, which implies that a given tag may verify under multiple keys. However, assuming AEGIS is key-committing, finding equivalent keys is expected to be significantly more difficult than for authentication schemes based on polynomial evaluation, such as GCM and Poly1305. Denis, et al. Expires 6 February 2023 [Page 20] Internet-Draft The AEGIS family of authenticated encryp August 2022 Under the assumption that the secret key is unknown to the attacker and the tag is not truncated, both AEGIS-128L and AEGIS-256 target 128-bit security against forgery attacks. Both algorithms MUST be used in a nonce-respecting setting: for a given key, a nonce MUST only be used once. Failure to do so would immediately reveal the bitwise difference between two messages. If tag verification fails, the decrypted message and wrong message authentication tag MUST NOT be given as output. As shown in the analysis of the (robustness of CAESAR candidates beyond their guarantees)[CRA18], even a partial leak of the plaintext without verification would facilitate chosen ciphertext attacks. Every key MUST be randomly chosen from a uniform distribution. The nonce MAY be public or predictable. It can be a counter, the output of a permutation, or a generator with a long period. With AEGIS-128L, random nonces can safely encrypt up to 2^48 messages using the same key with negligible collision probability. With AEGIS-256, random nonces can be used with no practical limits. The security of AEGIS against timing and physical attacks is limited by the implementation of the underlying AESRound() function. Failure to implement AESRound() in a fashion safe against timing and physical attacks, such as differential power analysis, timing analysis or fault injection attacks, may lead to leakage of secret key material or state information. The exact mitigations required for timing and physical attacks also depend on the threat model in question. Security analyses of AEGIS can be found in Chapter 4 of [AEGIS], in [Min14], in [ENP19], in [LIMS21], and in [JLD21]. 7. IANA Considerations IANA is requested to assign entries for AEAD_AEGIS128L and AEAD_AEGIS256 in the AEAD Registry with this document as reference. 8. References 8.1. Normative References Denis, et al. Expires 6 February 2023 [Page 21] Internet-Draft The AEGIS family of authenticated encryp August 2022 [FIPS-AES] NIST, "Advanced encryption standard (AES)", NIST Federal Information Processing Standards Publications 197, DOI 10.6028/NIST.FIPS.197, November 2001, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 8.2. Informative References [AEGIS] Wu, H. and B. Preneel, "AEGIS: A fast encryption algorithm (v1.1)", 15 September 2016, . [CRA18] Vaudenay, S. and D. Vizár, "Can Caesar Beat Galois? Robustness of CAESAR Candidates against Nonce Reusing and High Data Complexity Attacks", Applied Cryptography and Network Security. ACNS 2018. Lecture Notes in Computer Science, vol 10892, pp. 476–494, DOI 10.1007/978-3-319-93387-0_25, 2018, . [ENP19] Eichlseder, M., Nageler, M., and R. Primas, "Analyzing the Linear Keystream Biases in AEGIS", IACR Transactions on Symmetric Cryptology, 2019(4), pp. 348–368, DOI 10.13154/tosc.v2019.i4.348-368, 31 January 2020, . [JLD21] Jiao, L., Li, Y., and S. Du, "Guess-and-Determine Attacks on AEGIS", The Computer Journal, DOI 10.1093/comjnl/bxab059, 22 May 2021, . Denis, et al. Expires 6 February 2023 [Page 22] Internet-Draft The AEGIS family of authenticated encryp August 2022 [LGR21] Len, J., Grubbs, P., and T. Ristenpart, "Partitioning Oracle Attacks", 30th USENIX Security Symposium (USENIX Security 21), pp. 195–212, 2021, . [LIMS21] Liu, F., Isobe, T., Meier, W., and K. Sakamoto, "Weak Keys in Reduced AEGIS and Tiaoxin", IACR Transactions on Symmetric Cryptology, 2021(2), pp. 104–139, DOI 10.46586/tosc.v2021.i2.104-139, 2021, . [Min14] Minaud, B., "Linear Biases in AEGIS Keystream", Selected Areas in Cryptography. SAC 2014. Lecture Notes in Computer Science, vol 8781, pp. 290–305, DOI 10.1007/978-3-319-13051-4_18, 2014, . Appendix A. Test Vectors A.1. AESRound Test Vector in : 000102030405060708090a0b0c0d0e0f rk : 101112131415161718191a1b1c1d1e1f out : 7a7b4e5638782546a8c0477a3b813f43 A.2. AEGIS-128L Test Vectors A.2.1. Update Test Vector Denis, et al. Expires 6 February 2023 [Page 23] Internet-Draft The AEGIS family of authenticated encryp August 2022 S0 : 9b7e60b24cc873ea894ecc07911049a3 S1 : 330be08f35300faa2ebf9a7b0d274658 S2 : 7bbd5bd2b049f7b9b515cf26fbe7756c S3 : c35a00f55ea86c3886ec5e928f87db18 S4 : 9ebccafce87cab446396c4334592c91f S5 : 58d83e31f256371e60fc6bb257114601 S6 : 1639b56ea322c88568a176585bc915de S7 : 640818ffb57dc0fbc2e72ae93457e39a M0 : 033e6975b94816879e42917650955aa0 M1 : 033e6975b94816879e42917650955aa0 After Update: S0 : 596ab773e4433ca0127c73f60536769d S1 : 790394041a3d26ab697bde865014652d S2 : 38cf49e4b65248acd533041b64dd0611 S3 : 16d8e58748f437bfff1797f780337cee S4 : 69761320f7dd738b281cc9f335ac2f5a S5 : a21746bb193a569e331e1aa985d0d729 S6 : 09d714e6fcf9177a8ed1cde7e3d259a6 S7 : 61279ba73167f0ab76f0a11bf203bdff A.2.2. Test Vector 1 key : 10010000000000000000000000000000 nonce: 10000200000000000000000000000000 ad : msg : 00000000000000000000000000000000 ct : c1c0e58bd913006feba00f4b3cc3594e tag : abe0ece80c24868a226a35d16bdae37a A.2.3. Test Vector 2 Denis, et al. Expires 6 February 2023 [Page 24] Internet-Draft The AEGIS family of authenticated encryp August 2022 key : 10010000000000000000000000000000 nonce: 10000200000000000000000000000000 ad : msg : ct : tag : c2b879a67def9d74e6c14f708bbcc9b4 A.2.4. Test Vector 3 key : 10010000000000000000000000000000 nonce: 10000200000000000000000000000000 ad : 0001020304050607 msg : 000102030405060708090a0b0c0d0e0f 101112131415161718191a1b1c1d1e1f ct : 79d94593d8c2119d7e8fd9b8fc77845c 5c077a05b2528b6ac54b563aed8efe84 tag : cc6f3372f6aa1bb82388d695c3962d9a A.2.5. Test Vector 4 key : 10010000000000000000000000000000 nonce: 10000200000000000000000000000000 ad : 0001020304050607 msg : 000102030405060708090a0b0c0d ct : 79d94593d8c2119d7e8fd9b8fc77 tag : 5c04b3dba849b2701effbe32c7f0fab7 A.2.6. Test Vector 5 Denis, et al. Expires 6 February 2023 [Page 25] Internet-Draft The AEGIS family of authenticated encryp August 2022 key : 10010000000000000000000000000000 nonce: 10000200000000000000000000000000 ad : 000102030405060708090a0b0c0d0e0f 101112131415161718191a1b1c1d1e1f 20212223242526272829 msg : 101112131415161718191a1b1c1d1e1f 202122232425262728292a2b2c2d2e2f 3031323334353637 ct : b31052ad1cca4e291abcf2df3502e6bd b1bfd6db36798be3607b1f94d34478aa 7ede7f7a990fec10 tag : 7542a745733014f9474417b337399507 A.2.7. Test Vector 6 This test MUST return a "verification failed" error. key : 10000200000000000000000000000000 nonce: 10010000000000000000000000000000 ad : 0001020304050607 ct : 79d94593d8c2119d7e8fd9b8fc77 tag : 5c04b3dba849b2701effbe32c7f0fab7 A.2.8. Test Vector 7 This test MUST return a "verification failed" error. key : 10010000000000000000000000000000 nonce: 10000200000000000000000000000000 ad : 0001020304050607 ct : 79d94593d8c2119d7e8fd9b8fc78 tag : 5c04b3dba849b2701effbe32c7f0fab7 Denis, et al. Expires 6 February 2023 [Page 26] Internet-Draft The AEGIS family of authenticated encryp August 2022 A.2.9. Test Vector 8 This test MUST return a "verification failed" error. key : 10010000000000000000000000000000 nonce: 10000200000000000000000000000000 ad : 0001020304050608 ct : 79d94593d8c2119d7e8fd9b8fc77 tag : 5c04b3dba849b2701effbe32c7f0fab7 A.2.10. Test Vector 9 This test MUST return a "verification failed" error. key : 10010000000000000000000000000000 nonce: 10000200000000000000000000000000 ad : 0001020304050607 ct : 79d94593d8c2119d7e8fd9b8fc77 tag : 6c04b3dba849b2701effbe32c7f0fab8 A.3. AEGIS-256 Test Vectors A.3.1. Update Test Vector S0 : 1fa1207ed76c86f2c4bb40e8b395b43e S1 : b44c375e6c1e1978db64bcd12e9e332f S2 : 0dab84bfa9f0226432ff630f233d4e5b S3 : d7ef65c9b93e8ee60c75161407b066e7 S4 : a760bb3da073fbd92bdc24734b1f56fb S5 : a828a18d6a964497ac6e7e53c5f55c73 M : b165617ed04ab738afb2612c6d18a1ec After Update: S0 : e6bc643bae82dfa3d991b1b323839dcd S1 : 648578232ba0f2f0a3677f617dc052c3 S2 : ea788e0e572044a46059212dd007a789 S3 : 2f1498ae19b80da13fba698f088a8590 S4 : a54c2ee95e8c2a2c3dae2ec743ae6b86 S5 : a3240fceb68e32d5d114df1b5363ab67 Denis, et al. Expires 6 February 2023 [Page 27] Internet-Draft The AEGIS family of authenticated encryp August 2022 A.3.2. Test Vector 1 key : 10010000000000000000000000000000 00000000000000000000000000000000 nonce: 10000200000000000000000000000000 00000000000000000000000000000000 ad : msg : 00000000000000000000000000000000 ct : 754fc3d8c973246dcc6d741412a4b236 tag : 3fe91994768b332ed7f570a19ec5896e A.3.3. Test Vector 2 key : 10010000000000000000000000000000 00000000000000000000000000000000 nonce: 10000200000000000000000000000000 00000000000000000000000000000000 ad : msg : ct : tag : e3def978a0f054afd1e761d7553afba3 A.3.4. Test Vector 3 Denis, et al. Expires 6 February 2023 [Page 28] Internet-Draft The AEGIS family of authenticated encryp August 2022 key : 10010000000000000000000000000000 00000000000000000000000000000000 nonce: 10000200000000000000000000000000 00000000000000000000000000000000 ad : 0001020304050607 msg : 000102030405060708090a0b0c0d0e0f 101112131415161718191a1b1c1d1e1f ct : f373079ed84b2709faee373584585d60 accd191db310ef5d8b11833df9dec711 tag : 8d86f91ee606e9ff26a01b64ccbdd91d A.3.5. Test Vector 4 key : 10010000000000000000000000000000 00000000000000000000000000000000 nonce: 10000200000000000000000000000000 00000000000000000000000000000000 ad : 0001020304050607 msg : 000102030405060708090a0b0c0d ct : f373079ed84b2709faee37358458 tag : c60b9c2d33ceb058f96e6dd03c215652 A.3.6. Test Vector 5 Denis, et al. Expires 6 February 2023 [Page 29] Internet-Draft The AEGIS family of authenticated encryp August 2022 key : 10010000000000000000000000000000 00000000000000000000000000000000 nonce: 10000200000000000000000000000000 00000000000000000000000000000000 ad : 000102030405060708090a0b0c0d0e0f 101112131415161718191a1b1c1d1e1f 20212223242526272829 msg : 101112131415161718191a1b1c1d1e1f 202122232425262728292a2b2c2d2e2f 3031323334353637 ct : 57754a7d09963e7c787583a2e7b859bb 24fa1e04d49fd550b2511a358e3bca25 2a9b1b8b30cc4a67 tag : ab8a7d53fd0e98d727accca94925e128 A.3.7. Test Vector 6 This test MUST return a "verification failed" error. key : 10000200000000000000000000000000 00000000000000000000000000000000 nonce: 10010000000000000000000000000000 00000000000000000000000000000000 ad : 0001020304050607 ct : f373079ed84b2709faee37358458 tag : c60b9c2d33ceb058f96e6dd03c215652 A.3.8. Test Vector 7 This test MUST return a "verification failed" error. Denis, et al. Expires 6 February 2023 [Page 30] Internet-Draft The AEGIS family of authenticated encryp August 2022 key : 10010000000000000000000000000000 00000000000000000000000000000000 nonce: 10000200000000000000000000000000 00000000000000000000000000000000 ad : 0001020304050607 ct : f373079ed84b2709faee37358459 tag : c60b9c2d33ceb058f96e6dd03c215652 A.3.9. Test Vector 8 This test MUST return a "verification failed" error. key : 10010000000000000000000000000000 00000000000000000000000000000000 nonce: 10000200000000000000000000000000 00000000000000000000000000000000 ad : 0001020304050608 ct : f373079ed84b2709faee37358458 tag : c60b9c2d33ceb058f96e6dd03c215652 A.3.10. Test Vector 9 This test MUST return a "verification failed" error. key : 10010000000000000000000000000000 00000000000000000000000000000000 nonce: 10000200000000000000000000000000 00000000000000000000000000000000 ad : 0001020304050607 ct : f373079ed84b2709faee37358458 tag : d60b9c2d33ceb058f96e6dd03c215653 Acknowledgments The AEGIS authenticated encryption algorithm was invented by Hongjun Wu and Bart Preneel. Denis, et al. Expires 6 February 2023 [Page 31] Internet-Draft The AEGIS family of authenticated encryp August 2022 The round function leverages the AES permutation invented by Joan Daemen and Vincent Rijmen. They also authored the Pelican MAC that partly motivated the design of the AEGIS MAC. We would like to thank Eric Lagergren and Daniel Bleichenbacher for catching a broken test vector and Daniel Bleichenbacher for many helpful suggestions. Authors' Addresses Frank Denis Fastly Inc. Email: fde@00f.net Fabio Enrico Renzo Scotoni Individual Contributor Email: fabio@esse.ch Samuel Lucas Individual Contributor Email: samuel-lucas6@pm.me Denis, et al. Expires 6 February 2023 [Page 32]