Network Working Group S. Smyshlyaev, Ed. Internet-Draft CryptoPro Intended status: Informational V. Nozdrunov Expires: April 22, 2019 V. Shishkin TC 26 October 19, 2018 Multilinear Galois Mode (MGM) draft-smyshlyaev-mgm-09 Abstract Multilinear Galois Mode (MGM) is an authenticated encryption with associated data block cipher mode based on EtM principle. MGM is defined for use with 64-bit and 128-bit block ciphers. 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 April 22, 2019. Copyright Notice Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved. 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 Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Smyshlyaev, et al. Expires April 22, 2019 [Page 1]

Internet-Draft Multilinear Galois Mode (MGM) October 2018 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Existing Constructions . . . . . . . . . . . . . . . . . 2 2. Conventions Used in This Document . . . . . . . . . . . . . . 2 3. Basic Terms and Definitions . . . . . . . . . . . . . . . . . 2 4. Specification . . . . . . . . . . . . . . . . . . . . . . . . 4 4.1. MGM Encryption and Authentication Procedure . . . . . . . 4 4.2. MGM Decryption and Authentication Check Procedure . . . . 6 5. Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 6.1. Normative References . . . . . . . . . . . . . . . . . . 8 6.2. Informative References . . . . . . . . . . . . . . . . . 8 Appendix A. Test Vectors . . . . . . . . . . . . . . . . . . . . 8 Appendix B. Contributors . . . . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 1. Introduction Multilinear Galois Mode (MGM) is an authenticated encryption with associated data block cipher mode based on EtM principle. MGM is defined for use with 64-bit and 128-bit block. The MGM design principles can easily be applied to other block sizes. 1.1. Existing Constructions The text will be added in the future versions of the draft. 2. Conventions Used in This Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 3. Basic Terms and Definitions This document uses the following terms and definitions for the sets and operations on the elements of these sets: V* the set of all bit strings of a finite length (hereinafter referred to as strings), including the empty string; substrings and string components are enumerated from right to left starting from zero; V_s the set of all bit strings of length s, where s is a non- negative integer; Smyshlyaev, et al. Expires April 22, 2019 [Page 2]

Internet-Draft Multilinear Galois Mode (MGM) October 2018 |X| the bit length of the bit string X (if X is an empty string, then |X| = 0); X || Y concatenation of strings X and Y both belonging to V*, i.e., a string from V_{|X|+|Y|}, where the left substring from V_{|X|} is equal to X, and the right substring from V_{|Y|} is equal to Y; a^s the string in V_s that consists of s 'a' bits: a^s = (a, a, ... , a), 'a' in V_1; (xor) exclusive-or of the two bit strings of the same length, Z_{2^s} ring of residues modulo 2^s; MSB_i: V_s -> V_i the transformation that maps the string X = (x_{s-1}, ... , x_0) in V_s into the string MSB_i(X) = (x_{s-1}, ... , x_{s-i}) in V_i, i <= s, (most significant bits); Int_s: V_s -> Z_{2^s} the transformation that maps a string X = (x_{s-1}, ... , x_0) in V_s into the integer Int_s(X) = 2^{s-1} * x_{s-1} + ... + 2 * x_1 + x_0 (the interpretation of the bit string as an integer); Vec_s: Z_{2^s} -> V_s the transformation inverse to the mapping Int_s (the interpretation of an integer as a bit string); E_K: V_n -> V_n the block cipher permutation under the key K in V_k; k the bit length of the block cipher key; n the block size of the block cipher (in bits); len: V_s -> V_{n/2} the transformation that maps a string X in V_s, 0 <= s <= 2^{n/2} - 1, into the string len(X) = Vec_{n/2}(|X|) in V_{n/2}, where n is the block size of the used block cipher; [+] the addition operation in Z_{2^{n/2}}, where n is the block size of the used block cipher; (x) multiplication in GF(2^n), where n is the block size of the used block cipher; if n = 64, then the field polynomial is equal to f = x^64 + x^4 + x^3 + x + 1; if n = 128, then the field polynomial is equal to f = x^128 + x^7 + x^2 + x + 1; Smyshlyaev, et al. Expires April 22, 2019 [Page 3]

Internet-Draft Multilinear Galois Mode (MGM) October 2018 incr_l: V_n -> V_n the transformation that maps a string L || R, where L, R in V_{n/2}, into the string incr_l(L || R ) = Vec_{n/2}(Int_{n/2}(L) [+] 1) || R; incr_r: V_n -> V_n the transformation that maps a string L || R, where L, R in V_{n/2}, into the string incr_r(L || R ) = L || Vec_{n/2}(Int_{n/2}(R) [+] 1). 4. Specification An additional parameter that defines the functioning of MGM mode is the size S of the authentication field (in bits). The value of S MUST be fixed for a particular protocol, 32 <= S <= 128. The choice of the value S involves a trade-off between message expansion and the probability that an attacker can modify a message undetectably. 4.1. MGM Encryption and Authentication Procedure The MGM encryption and authentication procedure takes the following parameters as inputs: 1. Encryption key K in V_k. 2. Initial counter nonce ICN in V_{n-1}. 3. Plaintext P, 0 <= |P| < 2^{n/2}. If |P| > 0, then P = P_1 || ... || P*_q, P_i in V_n, i = 1, ... , q - 1, P*_q in V_u, 1 <= u <= n. If |P| = 0, then by definition P*_q is empty, q = 0, and u = n. 4. Associated authenticated data A, 0 <= |A| < 2^{n/2}. If |A| > 0, then A = A_1 || ... || A*_h, A_j in V_n, j = 1, ... , h - 1, A*_h in V_t, 1 <= t <= n. If |A| = 0, then by definition A*_h is empty, h = 0, and t = n. The associated data is authenticated but is not encrypted. The MGM encryption and authentication procedure outputs the following parameters: 1. Initial counter nonce ICN. 2. Associated authenticated data A. 3. Ciphertext C in V_{|P|}. 4. Authentication tag T in V_S. Smyshlyaev, et al. Expires April 22, 2019 [Page 4]

Internet-Draft Multilinear Galois Mode (MGM) October 2018 The MGM encryption and authentication procedure consists of the following steps: +----------------------------------------------------------------+ | MGM-Encrypt(K, ICN, P, A) | |----------------------------------------------------------------| | 1. Encryption step: | | - Y_1 = E_K(0^1 || ICN), | | - For i = 2, 3, ... , q do | | Y_i = incr_r(Y_{i-1}), | | - For i = 1, 2, ... , q - 1 do | | C_i = P_i (xor) E_K(Y_i), | | - C*_q = P*_q (xor) MSB_u(E_K(Y_q)), | | - C = C_1 || ... || C*_q. | | | | 2. Padding step: | | - A_h = A*_h || 0^{n-t}, | | - C_q = C*_q || 0^{n-u}. | | | | 3. Authentication tag T generation step: | | - Z_1 = E_K(1^1 || ICN), | | - sum = 0, | | - For i = 1, 2, ..., h do | | H_i = E_K(Z_i), | | sum = sum (xor) H_i (x) A_i, | | Z_{i+1} = incr_l(Z_i), | | - For j = 1, 2, ..., q do | | H_{h+j} = E_K(Z_{h+j}), | | sum = sum (xor) H_{h+j} (x) C_j, | | Z_{h+j+1} = incr_l(Z_{h+j}), | | - H_{h+q+1} = E_K(Z_{h+q+1}), | | - T = MSB_S(E_K(sum (xor) H_{h+q+1} (x) | | (len(A) || len(C)))). | | | | 4. Return (ICN, A, C, T). | |----------------------------------------------------------------+ The ICN value for each message that is encrypted under the given key K must be chosen in a unique manner. Using the same ICN values for two different messages encrypted with the same key eliminates the security properties of this mode. Users who do not wish to encrypt plaintext can provide a string P of length zero. Users who do not wish to authenticate associated data can provide a string A of length zero. The length of the associated Smyshlyaev, et al. Expires April 22, 2019 [Page 5]

Internet-Draft Multilinear Galois Mode (MGM) October 2018 data A and of the plaintext P MUST be such that 0 < |A| + |P| < 2^{n/2}. 4.2. MGM Decryption and Authentication Check Procedure The MGM decryption and authentication procedure takes the following parameters as inputs: 1. The encryption key K in V_k. 2. The initial counter nonce ICN in V_{n-1}. 3. The associated authenticated data A, 0 <= |A| < 2^{n/2}. A = A_1 || ... || A*_h, A_j in V_n, j = 1, ... , h - 1, A*_h in V_t, 1 <= t <= n. 4. The ciphertext C, 0 <= |C| < 2^{n/2}. C = C_1 || ... || C*_q, C_i in V_n, i = 1, ... , q - 1, C*_q in V_u, 1 <= u <= n. 5. The authenticated tag T in V_S. The MGM decryption and authentication procedure outputs FAIL or the following parameters: 1. Plaintext P in V_{|C|}. 2. Associated authenticated data A. The MGM decryption and authentication procedure consists of the following steps: Smyshlyaev, et al. Expires April 22, 2019 [Page 6]

Internet-Draft Multilinear Galois Mode (MGM) October 2018 +----------------------------------------------------------------+ | MGM-Decrypt(K, ICN, A, C, T) | |----------------------------------------------------------------| | 1. Padding step: | | - A_h = A*_h || 0^{n-t}, | | - C_q = C*_q || 0^{n-u}. | | | | 2. Authentication tag T' generation step: | | - Z_1 = E_K(1^1 || ICN), | | - sum1 = 0, sum2 = 0, | | - For i = 1, 2, ..., h do | | H_i = E_K(Z_i), | | sum1 = sum1 (xor) H_i (x) A_i, | | Z_{i+1} = incr_l(Z_i), | | - For j = 1, 2, ..., q do | | H_{h+j} = E_K(Z_{h+j}), | | sum2 = sum2 (xor) H_{h+j} (x) C_j, | | Z_{h+j+1} = incr_l(Z_{h+j}), | | - H_{h+q+1} = E_K(Z_{h+q+1}), | | - T' = MSB_S(E_K(sum1 (xor) sum2 (xor) | | H_{h+q+1} (x) (len(A) || len(C)))), | | - If T' != T then return FAIL | | return FAIL. | | | | 3. Decryption step: | | - Y_1 = E_K(0^1 || ICN), | | - For i = 2, 3, ... , q do | | Y_i = incr_r(Y_{i-1}), | | - For i = 1, 2, ... , q - 1 do | | P_i = C_i (xor) E_K(Y_i), | | - P*_q = C*_q (xor) MSB_u(E_K(Y_q)), | | - P = P_1 || ... || P*_q. | | | | 4. Return (P, A). | |----------------------------------------------------------------+ 5. Rationale The MGM mode was originally proposed in [PDMODE]. The MGM mode is designed to be fast, parallelizable, inverse free, online and secure. The MGM is based on counters for the reasons of performance. The first counter (Y_i, see Section 4.1) is used for message encryption, the second counter (H_i, see Section 4.1) is used for authentication. The second counter is encrypted eliminating the chance of obtaining Smyshlyaev, et al. Expires April 22, 2019 [Page 7]

Internet-Draft Multilinear Galois Mode (MGM) October 2018 any information about the H_k value in case when the H_l value is known to the adversary ( here l is not equal to k ). To provide parallelizable authentication a multilinear function is used. To avoid attacks based on padding and linear properties of multilinear function the lengths of associated data A, encrypted message C, and encrypting authentication tag is added. A collision of "usual" counters leads to obtaining the information about the H_i values and possible authentication vulnerabilities. To minimize the probability of this event we change the principle of counters operating by using the functions incr_l and incr_r. To counteract finding collisions we encrypt initial values of both counters. 6. References 6.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>. [RFC7801] Dolmatov, V., Ed., "GOST R 34.12-2015: Block Cipher "Kuznyechik"", RFC 7801, DOI 10.17487/RFC7801, March 2016, <https://www.rfc-editor.org/info/rfc7801>. 6.2. Informative References [GOST3412-2015] Federal Agency on Technical Regulating and Metrology, "Information technology. Cryptographic data security. Block ciphers", GOST R 34.12-2015, 2015. [PDMODE] Vladislav Nozdrunov, "Parallel and double block cipher mode of operation (PD-mode) for authenticated encryption", CTCrypt 2017 proceedings, pp. 36-45, 2017. Appendix A. Test Vectors Test vectors for the Kuznyechik block cipher (n = 128, k = 256) defined in [GOST3412-2015] (the English version can be found in [RFC7801]). Smyshlyaev, et al. Expires April 22, 2019 [Page 8]

Internet-Draft Multilinear Galois Mode (MGM) October 2018 Encryption key K: 00000: 88 99 AA BB CC DD EE FF 00 11 22 33 44 55 66 77 00010: FE DC BA 98 76 54 32 10 01 23 45 67 89 AB CD EF Associated authenticated data A: 00000: 02 02 02 02 02 02 02 02 01 01 01 01 01 01 01 01 00010: 04 04 04 04 04 04 04 04 03 03 03 03 03 03 03 03 00020: EA 05 05 05 05 05 05 05 05 Plaintext P: 00000: 11 22 33 44 55 66 77 00 FF EE DD CC BB AA 99 88 00010: 00 11 22 33 44 55 66 77 88 99 AA BB CC EE FF 0A 00020: 11 22 33 44 55 66 77 88 99 AA BB CC EE FF 0A 00 00030: 22 33 44 55 66 77 88 99 AA BB CC EE FF 0A 00 11 00040: AA BB CC 1. Encryption step: 0^1 || ICN: 00000: 11 22 33 44 55 66 77 00 FF EE DD CC BB AA 99 88 Y_1: 00000: 7F 67 9D 90 BE BC 24 30 5A 46 8D 42 B9 D4 ED CD E_K(Y_1): 00000: B8 57 48 C5 12 F3 19 90 AA 56 7E F1 53 35 DB 74 Y_2: 00000: 7F 67 9D 90 BE BC 24 30 5A 46 8D 42 B9 D4 ED CE E_K(Y_2): 00000: 80 64 F0 12 6F AC 9B 2C 5B 6E AC 21 61 2F 94 33 Y_3: 00000: 7F 67 9D 90 BE BC 24 30 5A 46 8D 42 B9 D4 ED CF E_K(Y_3): 00000: 58 58 82 1D 40 C0 CD 0D 0A C1 E6 C2 47 09 8F 1C Y_4: 00000: 7F 67 9D 90 BE BC 24 30 5A 46 8D 42 B9 D4 ED D0 E_K(Y_4): 00000: E4 3F 50 81 B5 8F 0B 49 01 2F 8E E8 6A CD 6D FA Y_5: 00000: 7F 67 9D 90 BE BC 24 30 5A 46 8D 42 B9 D4 ED D1 E_K(Y_5): 00000: 86 CE 9E 2A 0A 12 25 E3 33 56 91 B2 0D 5A 33 48 C: 00000: A9 75 7B 81 47 95 6E 90 55 B8 A3 3D E8 9F 42 FC Smyshlyaev, et al. Expires April 22, 2019 [Page 9]

Internet-Draft Multilinear Galois Mode (MGM) October 2018 00010: 80 75 D2 21 2B F9 FD 5B D3 F7 06 9A AD C1 6B 39 00020: 49 7A B1 59 15 A6 BA 85 93 6B 5D 0E A9 F6 85 1C 00030: C6 0C 14 D4 D3 F8 83 D0 AB 94 42 06 95 C7 6D EB 00040: 2C 75 52 2. Padding step: A_1 || ... || A_h: 00000: 02 02 02 02 02 02 02 02 01 01 01 01 01 01 01 01 00010: 04 04 04 04 04 04 04 04 03 03 03 03 03 03 03 03 00020: EA 05 05 05 05 05 05 05 05 00 00 00 00 00 00 00 C_1 || ... || C_q: 00000: A9 75 7B 81 47 95 6E 90 55 B8 A3 3D E8 9F 42 FC 00010: 80 75 D2 21 2B F9 FD 5B D3 F7 06 9A AD C1 6B 39 00020: 49 7A B1 59 15 A6 BA 85 93 6B 5D 0E A9 F6 85 1C 00030: C6 0C 14 D4 D3 F8 83 D0 AB 94 42 06 95 C7 6D EB 00040: 2C 75 52 00 00 00 00 00 00 00 00 00 00 00 00 00 3. Authentication tag T generation step: 1^1 || ICN: 00000: 91 22 33 44 55 66 77 00 FF EE DD CC BB AA 99 88 Z_1: 00000: 7F C2 45 A8 58 6E 66 02 A7 BB DB 27 86 BD C6 6F H_1: 00000: 8D B1 87 D6 53 83 0E A4 BC 44 64 76 95 2C 30 0B current sum: 00000: 4C F4 27 F4 AD B7 5C F4 C0 DA 39 D5 AB 48 CF 38 Z_2: 00000: 7F C2 45 A8 58 6E 66 03 A7 BB DB 27 86 BD C6 6F H_2: 00000: 7A 24 F7 26 30 E3 76 37 21 C8 F3 CD B1 DA 0E 31 current sum: 00000: 94 95 44 0E F6 24 A1 DD C6 F5 D9 77 28 50 C5 73 Z_3: 00000: 7F C2 45 A8 58 6E 66 04 A7 BB DB 27 86 BD C6 6F H_3: 00000: 44 11 96 21 17 D2 06 35 C5 25 E0 A2 4D B4 B9 0A current sum: 00000: A4 9A 8C D8 A6 F2 74 23 DB 79 E4 4A B3 06 D9 42 Z_4: 00000: 7F C2 45 A8 58 6E 66 05 A7 BB DB 27 86 BD C6 6F Smyshlyaev, et al. Expires April 22, 2019 [Page 10]

Internet-Draft Multilinear Galois Mode (MGM) October 2018 H_4: 00000: D8 C9 62 3C 4D BF E8 14 CE 7C 1C 0C EA A9 59 DB current sum: 00000: 09 FE 3F 6A 83 3C 21 B3 90 27 D0 20 6A 84 E1 5A Z_5: 00000: 7F C2 45 A8 58 6E 66 06 A7 BB DB 27 86 BD C6 6F H_5: 00000: A5 E1 F1 95 33 3E 14 82 96 99 31 BF BE 6D FD 43 current sum: 00000: B5 DA 26 BB 00 EB A8 04 35 D7 97 6B C6 B5 46 4D Z_6: 00000: 7F C2 45 A8 58 6E 66 07 A7 BB DB 27 86 BD C6 6F H_6: 00000: B4 CA 80 8C AC CF B3 F9 17 24 E4 8A 2C 7E E9 D2 current sum: 00000: DD 1C 0E EE F7 83 C8 EB 2A 33 F3 58 D7 23 0E E5 Z_7: 00000: 7F C2 45 A8 58 6E 66 08 A7 BB DB 27 86 BD C6 6F H_7: 00000: 72 90 8F C0 74 E4 69 E8 90 1B D1 88 EA 91 C3 31 current sum: 00000: 89 6C E1 08 32 EB EA F9 06 9F 3F 73 76 59 4D 40 Z_8: 00000: 7F C2 45 A8 58 6E 66 09 A7 BB DB 27 86 BD C6 6F H_8: 00000: 23 CA 27 15 B0 2C 68 31 3B FD AC B3 9E 4D 0F B8 current sum: 00000: 99 1A F5 C9 D0 80 F7 63 87 FE 64 9E 7C 93 C6 42 Z_9: 00000: 7F C2 45 A8 58 6E 66 0A A7 BB DB 27 86 BD C6 6F H_9: 00000: BC BC E6 C4 1A A3 55 A4 14 88 62 BF 64 BD 83 0D len(A) || len(C): 00000: 00 00 00 00 00 00 01 48 00 00 00 00 00 00 02 18 sum (xor) H_9 (x) (len(A) || len(C)): 00000: C0 C7 22 DB 5E 0B D6 DB 25 76 73 83 3D 56 71 28 Tag T: 00000: CF 5D 65 6F 40 C3 4F 5C 46 E8 BB 0E 29 FC DB 4C Smyshlyaev, et al. Expires April 22, 2019 [Page 11]

Internet-Draft Multilinear Galois Mode (MGM) October 2018 Appendix B. Contributors o Evgeny Alekseev CryptoPro alekseev@cryptopro.ru o Ekaterina Smyshlyaeva CryptoPro ess@cryptopro.ru o Lilia Ahmetzyanova CryptoPro lah@cryptopro.ru o Grigory Marshalko TC 26 marshalko_gb@tc26.ru o Vladimir Rudskoy TC 26 rudskoy_vi@tc26.ru o Alexey Nesterenko National Research University Higher School of Economics anesterenko@hse.ru Authors' Addresses Stanislav Smyshlyaev (editor) CryptoPro Phone: +7 (495) 995-48-20 Email: svs@cryptopro.ru Vladislav Nozdrunov TC 26 Email: nozdrunov_vi@tc26.ru Vasily Shishkin TC 26 Email: shishkin_va@tc26.ru Smyshlyaev, et al. Expires April 22, 2019 [Page 12]