## SCA Extensions For OpenPGP

draft-ribose-openpgp-sca-00

Versions: (draft-ribose-openpgp-oscca)00

Internet Research Task Force R. Tse Internet-Draft Ribose Updates: 4880, 6637 (if approved) W. Wong Intended status: Standards Track Hang Seng Management College Expires: June 18, 2018 J. Lloyd D. Wyatt E. Borsboom Ribose December 15, 2017 SCA Extensions For OpenPGP draft-ribose-openpgp-sca-00 Abstract This document enables OpenPGP (RFC4880) to be used in a compliant manner according to regulations set by the SCA (the State Cryptography Administration of China) within China. Specifically, it extends OpenPGP to support the usage of SM2, SM3 and SM4 algorithms, and provides the SCA-compliant OpenPGP profile "SCA- SM234". 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 June 18, 2018. Copyright Notice Copyright (c) 2017 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 Tse, et al. Expires June 18, 2018 [Page 1]

Internet-Draft SCA Extensions for OpenPGP December 2017 (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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terms and Definitions . . . . . . . . . . . . . . . . . . . . 4 3. Symbols And Abbreviations . . . . . . . . . . . . . . . . . . 4 4. SM2 Algorithms . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. SM2 Digital Signature Algorithm . . . . . . . . . . . . . 6 4.2. SM2 Key Exchange Protocol . . . . . . . . . . . . . . . . 7 4.3. SM2 Public Key Encryption . . . . . . . . . . . . . . . . 7 4.4. Recommended SM2 Curve . . . . . . . . . . . . . . . . . . 7 4.4.1. Definitions . . . . . . . . . . . . . . . . . . . . . 8 4.4.2. Elliptic Curve Formula . . . . . . . . . . . . . . . 8 4.4.3. Curve Parameters . . . . . . . . . . . . . . . . . . 8 4.5. Data Formats . . . . . . . . . . . . . . . . . . . . . . 8 4.5.1. Secret Key Data Format . . . . . . . . . . . . . . . 8 4.5.2. Encrypted Data Format . . . . . . . . . . . . . . . . 9 4.5.3. Signature Data Format . . . . . . . . . . . . . . . . 9 5. SM3 Hash Algorithm . . . . . . . . . . . . . . . . . . . . . 10 6. SM4 Symmetric Encryption Algorithm . . . . . . . . . . . . . 10 7. Supported Algorithms . . . . . . . . . . . . . . . . . . . . 11 7.1. Public Key Algorithms . . . . . . . . . . . . . . . . . . 11 7.2. Symmetric Key Algorithms . . . . . . . . . . . . . . . . 11 7.3. Hash Algorithms . . . . . . . . . . . . . . . . . . . . . 12 8. Conversion Primitives . . . . . . . . . . . . . . . . . . . . 12 9. SM2 Key Derivation Function . . . . . . . . . . . . . . . . . 12 9.1. Prerequisites . . . . . . . . . . . . . . . . . . . . . . 13 9.2. Inputs . . . . . . . . . . . . . . . . . . . . . . . . . 13 9.3. Outputs . . . . . . . . . . . . . . . . . . . . . . . . . 13 10. Encoding of Public and Private Keys . . . . . . . . . . . . . 14 10.1. Public-Key Packet Formats . . . . . . . . . . . . . . . 14 10.2. Secret-Key Packet Formats . . . . . . . . . . . . . . . 15 11. Message Encoding with Public Keys . . . . . . . . . . . . . . 15 11.1. Public-Key Encrypted Session Key Packets (Tag 1) . . . . 15 11.2. Signature Packet (Tag 2) . . . . . . . . . . . . . . . . 16 11.2.1. Version 3 Signature Packet Format . . . . . . . . . 16 11.2.2. Version 4 Signature Packet Format . . . . . . . . . 16 12. SM2 ECC Curve OID . . . . . . . . . . . . . . . . . . . . . . 16 13. Compatibility Profiles . . . . . . . . . . . . . . . . . . . 17 13.1. SCA SM234 Profile . . . . . . . . . . . . . . . . . . . 17 14. Security Considerations . . . . . . . . . . . . . . . . . . . 17 15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 16. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 16.1. Normative References . . . . . . . . . . . . . . . . . . 18 Tse, et al. Expires June 18, 2018 [Page 2]

Internet-Draft SCA Extensions for OpenPGP December 2017 16.2. Informative References . . . . . . . . . . . . . . . . . 20 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 25 A.1. Public Key Example . . . . . . . . . . . . . . . . . . . 25 A.2. Signature Example . . . . . . . . . . . . . . . . . . . . 25 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 26 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26 1. Introduction SM2 [GBT.32918.1-2016] [I-D.shen-sm2-ecdsa], SM3 [GBT.32905-2016] [I-D.sca-cfrg-sm3] and kM4 [GBT.32907-2016] [I-D.ribose-cfrg-sm4] are cryptographic standards issued by the State Cryptography Administration [SCA] (formerly OSCCA, the Office of State Commercial Cryptography Administration of China) as authorized cryptographic algorithms for use within China. These algorithms are published in public. Adoption of this document enables exchange of OpenPGP-secured email [RFC4880] in a SCA-compliant manner through usage of the authorized combination of SM2, SM3 and SM4. SM2 is an elliptic curve cryptosystem (ECC) that is composed of a set of public key cryptographic algorithms based on elliptic curves and also a recommended elliptic curve: o Digital Signature Algorithm [GBT.32918.2-2016] o Key Exchange Protocol [GBT.32918.3-2016] o Public Key Encryption Algorithm [GBT.32918.4-2016] o SM2 Recommended Elliptic Curve [GBT.32918.5-2017] SM3 [GBT.32905-2016] is a hash algorithm designed for electronic authentication purposes. SM4 [GBT.32907-2016] is a symmetric encryption algorithm designed for data encryption. SM2, SM3 and SM4 are standardized at ISO as [ISO.IEC.14888-3], [ISO.IEC.10118-3], and [ISO.IEC.18033-3.AMD2] respectively. This document extends OpenPGP [RFC4880] and its ECC extension [RFC6637] to support SM2, SM3 and SM4: o support the SM3 hash algorithm for data validation purposes Tse, et al. Expires June 18, 2018 [Page 3]

Internet-Draft SCA Extensions for OpenPGP December 2017 o support signatures utilizing the combination of SM3 with other digital signing algorithms, such as RSA, ECDSA and SM2 o support the SM2 asymmetric encryption algorithm for public key operations o support usage of SM2 in combination with supported hash algorithms, such as SHA-256 and SM3 o support the SM4 symmetric encryption algorithm for data protection purposes o defines the OpenPGP profile "SCA-SM234" to enable usage of OpenPGP in an SCA-compliant manner. 2. Terms and Definitions 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]. Compliant applications are a subset of the broader set of OpenPGP applications described in [RFC4880]. Any [RFC2119] keyword within this document applies to compliant applications only. The following terms and definitions apply to this document. SCA-compliant All cryptographic algorithms used are compliant with SCA [SCA] regulations. SM2DSA The elliptic curve digital signature algorithm defined in [GBT.32918.2-2016] SM2KEP The elliptic curve key exchange protocol defined in [GBT.32918.3-2016] SM2PKE The public key encryption algorithm defined in [GBT.32918.4-2016] 3. Symbols And Abbreviations This document utilizes definitions of operations from [RFC7253] and are included here for reference. Tse, et al. Expires June 18, 2018 [Page 4]

Internet-Draft SCA Extensions for OpenPGP December 2017 c^i The integer c raised to the i-th power. S || T String S concatenated with string T (e.g., 000 || 111 == 000111). 4. SM2 Algorithms SM2 is an elliptic curve based cryptosystem (ECC) [GBT.32918.1-2016] [I-D.shen-sm2-ecdsa] published by [SCA]. It was first published by the SCA ("OSCCA" at that time) in public in 2010 [OSCCA-SM2], then standardized as [GMT-0003-2012] in 2012, included in [ISO.IEC.11889] in 2015, published as a Chinese National Standard as [GBT.32918.1-2016], and published in [ISO.IEC.14888-3] in 2017. The SM2 cryptosystem [I-D.shen-sm2-ecdsa] is published in 5 parts, covering: o Part 1: General [GBT.32918.1-2016] o Part 2: Digital Signature Algorithm [GBT.32918.2-2016] o Part 3: Key Exchange [GBT.32918.3-2016] o Part 4: Public Key Encryption Algorithm [GBT.32918.4-2016] o Part 5: Parameter Definition [GBT.32918.5-2017] Specifically, it is composed of three distinct algorithms: o an elliptical curve digital signature algorithm ("SM2DSA") [GBT.32918.2-2016] [ISO.IEC.14888-3] [SM2-2] o a key exchange protocol ("SM2KEP") [GBT.32918.3-2016]; and o a public key encryption algorithm ("SM2PKE") [GBT.32918.4-2016]. This document refers to the SM2DSA and SM2PKE algorithms for the usage of OpenPGP [RFC4880]. [GMT-0009-2012] provides specifications on interoperable usage of SM2 data formats, and they are adhered to within within this document. Tse, et al. Expires June 18, 2018 [Page 5]

Internet-Draft SCA Extensions for OpenPGP December 2017 4.1. SM2 Digital Signature Algorithm The SM2 Digital Signature Algorithm is intended for digital signature and verifications in commercial cryptographic applications, including, but not limited to: o identity authentication o protection of data integrity o verification of data authenticity The process of digital signature signing and verification along with their examples are found in [GBT.32918.2-2016], [ISO.IEC.14888-3], [SM2-2], and also described in [I-D.shen-sm2-ecdsa]. The SM2DSA process requires usage of a hash function within. For SCA-compliant usage, a SCA-compliant hash function such as SM3 [GBT.32905-2016] *MUST* also be used. Formal security proofs for SM2 are provided in [SM2-SigSecurity] indicating that it satisfies both EUF-CMA security and security against generalized strong key substitution attacks. The SM2DSA algorithm has been cryptanalyzed by multiple parties with the current strongest attack being nonce [SM2-DSA-Nonces] [SM2-DSA-Nonces2] and lattice attacks [SM2-DSA-Lattice]. In terms of OpenPGP usage, SM2DSA is an alternative to the ECDSA algorithm specified in [RFC6637]. For OpenPGP compatibility, these additional requirements *MUST* be adhered to: o SM2DSA allows use of an optional "user identity" string which is hashed into "ZA" (Section 3.5 of [SM2-2] and Section 5.1.4.4 of [I-D.shen-sm2-ecdsa]). In OpenPGP, the user identifier "IDA" *MUST* be the empty string. o While SM2DSA usually signs "H(ZA || msg)" (Section 4.1 of [SM2-2]), this document follows the OpenPGP convention of [RFC6637] of not directly signing the raw message "msg", but its hash "H(msg)". Therefore when a message is signed by SM2DSA in OpenPGP, the algorithm *MUST* sign the content of "H(ZA || H(msg))" instead of "H(ZA || msg)". The hash algorithm used here *MUST* be identical. Tse, et al. Expires June 18, 2018 [Page 6]

Internet-Draft SCA Extensions for OpenPGP December 2017 4.2. SM2 Key Exchange Protocol The SM2 Key Exchange Protocol is used for cryptographic key exchange, allowing the negotiation and exchange of a session key within two to three message transfers. The process of key exchange and verification along with their examples are found in [GBT.32918.3-2016] [SM2-3], and also described in [I-D.shen-sm2-ecdsa]. SM2KEP is not used with OpenPGP as it is a two- to three- pass key exchange mechanism, while in OpenPGP, public keys of recipients are available initially. The SM2KEP is now considered insecure due to [SM2-KEP-Comments], similar in status to the Unified Model and MQV schemes described in [NIST.SP.800-56Ar2]. 4.3. SM2 Public Key Encryption The SM2 Public Key Encryption algorithm is an elliptic curve based asymmetric encryption algorithm. It is used for cryptographic encryption and decryption, allowing the message sender to utilize the public key of the message receiver to encrypt the message, with the recipient decrypting the messaging using his private key. The full description of SM2PKE is provided in [GBT.32918.4-2016]. It utilizes a public key size of 512 bits and private key size of 256 bits [GBT.32918.4-2016] [GMT-0003-2012]. The process of encryption and decryption, along with their examples are found in [GBT.32918.4-2016] and [SM2-4]. The SM2PKE process requires usage of a hash function within. For SCA-compliant usage, a SCA-compliant hash function such as SM3 [GBT.32905-2016] *MUST* also be used. In OpenPGP, SM2PKE is an alternative to RSA specified in [RFC4880]. 4.4. Recommended SM2 Curve The recommended curve is specified in [GBT.32918.5-2017] [SM2-5] and provided here for reference. SM2 uses a 256-bit elliptic curve. Tse, et al. Expires June 18, 2018 [Page 7]

Internet-Draft SCA Extensions for OpenPGP December 2017 4.4.1. Definitions p an integer larger than 3 a, b elements of F_q, defines an elliptic curve E on F_q n Order of base point G (n is a prime factor of E(F_q)) x_G x-coordinate of generator G y_G y-coordinate of generator G 4.4.2. Elliptic Curve Formula y^2 = x^3 + ax + b 4.4.3. Curve Parameters p = FFFFFFFE FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF 00000000 FFFFFFFF FFFFFFFF a = FFFFFFFE FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF 00000000 FFFFFFFF FFFFFFFC b = 28E9FA9E 9D9F5E34 4D5A9E4B CF6509A7 F39789F5 15AB8F92 DDBCBD41 4D940E93 n = FFFFFFFE FFFFFFFF FFFFFFFF FFFFFFFF 7203DF6B 21C6052B 53BBF409 39D54123 x_G = 32C4AE2C 1F198119 5F990446 6A39C994 8FE30BBF F2660BE1 715A4589 334C74C7 y_G = BC3736A2 F4F6779C 59BDCEE3 6B692153 D0A9877C C62A4740 02DF32E5 2139F0A0 4.5. Data Formats [GMT-0009-2012] defines a number of data formats for the SM2 algorithm to allow interoperable implementations. This document adheres to these conventions. 4.5.1. Secret Key Data Format SM2 secret key data format is described in ASN.1 as [GMT-0009-2012]: SM2PrivateKey ::= INTEGER Tse, et al. Expires June 18, 2018 [Page 8]

Internet-Draft SCA Extensions for OpenPGP December 2017 SM2 public key data format is described in ASN.1 as [GMT-0009-2012]: SM2PublicKey ::= BIT STRING Where: o "SM2PublicKey" is of type "BIT STRING" and with content "04 || X || Y". * "X" and "Y" specifies the x- and y-coordinates of the public key, each of 256-bits long. 4.5.2. Encrypted Data Format The SM2 encrypted data format is provided by [GMT-0009-2012] as the following in ASN.1 format: SM2Cipher ::= SEQENCE{ XCoordinate INTEGER, -- x-coordinate YCoordinate INTEGER, -- y-coordinate HASH OCTET STRING SIZE(32), -- hash value CipherText OCTET STRING -- ciphertext } Where: o "XCoordinate" and "YCoordinate" are x- and y-coordinates on the elliptic curve, both 256 bits long. o "HASH" is the hash value calculated from the hash function used in "KDF" of a fixed bit length of 256-bits. o "CipherText" is of same length as its plaintext. 4.5.3. Signature Data Format SM2 signature data format is described in ASN.1 as [GMT-0009-2012]: SM2Signature ::= SEQUENCE{ R INTEGER, -- first portion of signature S INTEGER -- second portion of signature } "R" and "S" represent the first and second portion of the signature, and both are 256 bits long. Tse, et al. Expires June 18, 2018 [Page 9]

Internet-Draft SCA Extensions for OpenPGP December 2017 5. SM3 Hash Algorithm The SM3 Cryptographic Hash Algorithm [GBT.32905-2016] is an iterative hash function designed by Xiaoyun Wang et al., published by [SCA] as an alternative to SHA-2 [NIST.FIPS.180-4]. The specification, security considerations and cryptanalysis results of SM3 are thoroughly presented in [I-D.sca-cfrg-sm3]. It was first published by the SCA ("OSCCA" at that time) in public in 2010 [SM3], then published as an industry cryptogrpahic standard in 2012 [GMT-0004-2012], published as a Chinese National Standard in 2016 as [GBT.32905-2016], and included in the [ISO.IEC.10118-3] standard in 2017. The algorithm is designed to be used for commercial cryptographic applications including, but not limited to: o digital signatures and their verification o message authentication code generation and their verification o generation of random numbers SM3 has a Merkle-Damgard construction and is similar to SHA-2 [NIST.FIPS.180-4] of the MD4 [RFC6150] family, with the addition of several strengthening features including a more complex step function and stronger message dependency than SHA-256 [SM3-Boomerang]. SM3 produces an output hash value of 256 bits long, based on 512-bit input message blocks [GBT.32905-2016], on input lengths up to 2^(m). 6. SM4 Symmetric Encryption Algorithm SM4 [GBT.32907-2016] is a symmetric encryption algorithm designed by Shuwang Lu et al. originally intended for the usage of wireless local area network (Wireless LAN) products. The specification, security considerations and cryptanalysis results of SM4 are thoroughly presented in [I-D.ribose-cfrg-sm4] . SM4 is a 128-bit blockcipher, uses a key size of 128 bits and internally uses an 8-bit S-box. It performs 32 rounds per block. Decryption is achieved by reversing the order of encryption. SMS4 was first published in public as part of WAPI (Wired Authentication and Privacy Infrastructure), the Chinese National Standard for Wireless LAN [GB.15629.11-2003]. It was then published Tse, et al. Expires June 18, 2018 [Page 10]

Internet-Draft SCA Extensions for OpenPGP December 2017 independently by SCA ("OSCCA" at that time) in 2006 [SM4], formally renamed to SM4 in 2012 [GMT-0002-2012], published as a Chinese National Standard in 2016 [GBT.32907-2016], and included in [ISO.IEC.18033-3.AMD2] in 2017. It is a required encryption algorithm specified in WAPI [GB.15629.11-2003]. 7. Supported Algorithms 7.1. Public Key Algorithms The SM2 algorithm is supported with the following extension. The following public key algorithm IDs are added to expand Section 9.1 of [RFC4880], "Public-Key Algorithms": +-----+--------------------------+ | ID | Description of Algorithm | +-----+--------------------------+ | TBD | SM2 | +-----+--------------------------+ Compliant applications *MUST* support both usages of SM2 Section 4: o SM2 Digital Signature Algorithm (SM2DSA) [GBT.32918.2-2016] o SM2 Public Key Encryption (SM2PKE) [GBT.32918.4-2016] 7.2. Symmetric Key Algorithms The SM4 algorithm is supported with the following extension. The following symmetric encryption algorithm ID is added to expand Section 9.2 of [RFC4880], "Symmetric-Key Algorithms": +-----+--------------------------+ | ID | Description of Algorithm | +-----+--------------------------+ | TBD | SM4 | +-----+--------------------------+ Compliant applications *MUST* support SM4 Section 6. Tse, et al. Expires June 18, 2018 [Page 11]

Internet-Draft SCA Extensions for OpenPGP December 2017 7.3. Hash Algorithms The SM3 algorithm is supported with the following extension. The following symmetric encryption algorithm IDs are added to expand Section 9.3 of [RFC4880], "Hash Algorithms": +-----+--------------------------+ | ID | Description of Algorithm | +-----+--------------------------+ | TBD | SM3 | +-----+--------------------------+ Compliant applications *MUST* support SM3 Section 5. 8. Conversion Primitives The encoding method of [RFC6637] Section 6 *MUST* be used, and is compatible with the definition given in [SEC1]. For clarity, according to the EC curve MPI encoding method of [RFC6637], the exact size of the MPI payload for the "SM2 Recommended" 256-bit curve [GBT.32918.5-2017], is 515 bits. 9. SM2 Key Derivation Function A key derivation function (KDF) is necessary to implement EC encryption. The SM2PKE KDF is defined in Section 3.4.3 of [GBT.32918.4-2016] (and Section 5.4.3 of [I-D.shen-sm2-ecdsa], Section 3.4.3 of [SM2-4]). For SCA-compliance, it *SHOULD* be used in conjunction with an SCA- approved hash algorithm, such as SM3 [GBT.32905-2016]. The SM2PKE KDF is equivalent to the KDF2 function defined in Section 13.2 of [IEEE.1363a.2004] given the following assignments: o Parameter * v as hBits, the output length of the selected hash function Hash o Input * KEYLEN as oBits * Z as the plaintext string; and Tse, et al. Expires June 18, 2018 [Page 12]

Internet-Draft SCA Extensions for OpenPGP December 2017 * PB is set to the empty bit string. Pseudocode of the SM2KDF function is provided here for convenience. This function contains edited variable names for clarity. 9.1. Prerequisites o Hash(S) is a hash function that outputs a v-bit long hash value based on input S. o MSB(b, S) is a function that outputs the b most significant bits of the bitstream S. o Floor(r) and Ceil(r) are the floor and ceiling functions respectively for the input of real number r. Both functions outputs an integer. 9.2. Inputs KEYLEN Desired key length. A positive integer less than (2^32 - 1) x v. Z Plaintext. String of any length. 9.3. Outputs K Generated key. String of length KEYLEN. K is defined as follows. Tse, et al. Expires June 18, 2018 [Page 13]

Internet-Draft SCA Extensions for OpenPGP December 2017 _____________________________________________________________________ Counter = 1 // a 32-bit counter n = KEYLEN / v for each 1 <= i <= Ceil(n) Ha_i = Hash( Z || Counter ) Counter = Counter + 1 end for if n is a whole number then Ha! = Ha_{Ceil(n)} else Ha! = MSB(KEYLEN - (v x Floor(n)), Ha_{Ceil(n)}) end if K = Ha_1 || Ha_2 || ... || Ha_{Ceil(n)-1} || Ha! _____________________________________________________________________ 10. Encoding of Public and Private Keys 10.1. Public-Key Packet Formats The following algorithm-specific packets are added to Section 5.5.2 of [RFC4880], "Public-Key Packet Formats", to support SM2DSA and SM2PKE. This document extends the algorithm-specific portion with the following fields. Algorithm-Specific Fields for SM2DSA keys: o a variable-length field containing a curve OID, formatted as follows: * a one-octet size of the following field; values 0 and 0xFF are reserved for future extensions * octets representing a curve OID, described in Section 12 o MPI of an EC point representing a public key Algorithm-Specific Fields for SM2PKE keys: o a variable-length field containing a curve OID, formatted as follows: Tse, et al. Expires June 18, 2018 [Page 14]

Internet-Draft SCA Extensions for OpenPGP December 2017 * a one-octet size of the following field; values 0 and 0xFF are reserved for future extensions * octets representing a curve OID, described in Section 12 o MPI of an EC point representing a public key Note that both SM2DSA and SM2PKE public keys are composed of the same sequence of fields, and use the same codepoint to identify them. They are distinguished by the key usage flags. 10.2. Secret-Key Packet Formats The following algorithm-specific packets are added to Section 5.5.3. of [RFC4880], "Secret-Key Packet Formats", to support SM2DSA and SM2PKE. This document extends the algorithm-specific portion with the following fields. Algorithm-Specific Fields for SM2DSA or SM2PKE secret keys: o an MPI of an integer representing the secret key, which is a scalar of the public EC point 11. Message Encoding with Public Keys 11.1. Public-Key Encrypted Session Key Packets (Tag 1) Section 5.1 of [RFC4880], "Public-Key Encrypted Session Key Packets (Tag 1)" is extended to support SM2PKE using the following algorithm specific fields for SM2PKE, through applying the KDF described in Section 9. Algorithm Specific Fields for SM2 encryption: o The SM2 ciphertext is formatted in the OpenPGP bitstream as a single MPI. This consists of: * The data format described in Section 4.5.2 containing data provided by [GBT.32918.4-2016] Section 6.1 step A8 ("C = (C1 || C3 || C2)"), followed by * a single octet giving the code for the hash algorithm used within the calculation of the KDF mask "t" (step A5 of [GBT.32918.4-2016] Section 6.1) and the calculation of "C3" (step A7 of [GBT.32918.4-2016] Section 6.1). For SCA compliance, this *MUST* be an SCA-approved hash function, and Tse, et al. Expires June 18, 2018 [Page 15]

Internet-Draft SCA Extensions for OpenPGP December 2017 in any case, it *SHOULD* be a hash which is listed in the receiving keys "Preferred Hash Algorithms" list (Section 5.2.3.8 of [RFC4880]). 11.2. Signature Packet (Tag 2) 11.2.1. Version 3 Signature Packet Format Section 5.2.2 of [RFC4880] defines the signature format for "Version 3 Signature Packet Format". Similar to ECDSA [RFC6637], no change in the format is necessary for SM2DSA. 11.2.2. Version 4 Signature Packet Format Section 5.2.3 of [RFC4880] defines the signature format for "Version 4 Signature Packet Format". Similar to ECDSA [RFC6637], no change in the format is necessary for SM2DSA. 12. SM2 ECC Curve OID This section provides the curve ASN.1 Object Identifier (OID) of the "SM2 Recommended Curve" [GBT.32918.5-2017] described in Section 4, according to the method of [RFC6637]. We specify the curve OID of the "SM2 Recommended Curve" to be the registered OID entry of "SM2 Elliptic Curve Cryptography" according to [GMT-0006-2012], which is "1.2.156.10197.1.301". The table below specifies the exact sequence of bytes of the mentioned curve: +---------------------+--------+--------------------+---------------+ | ASN.1 OID | OID | Curve OID bytes in | Curve name | | | len | hex | | +---------------------+--------+--------------------+---------------+ | 1.2.156.10197.1.301 | 8 | 2A 81 1C CF 55 01 | SM2 | | | | 82 2D | Recommended | +---------------------+--------+--------------------+---------------+ The complete ASN.1 DER encoding for the SM2 Recommended curve OID is "06 08 2A 81 1C CF 55 01 82 2D", from which the first entry in the table above is constructed by omitting the first two octets. Only the truncated sequence of octets is the valid representation of a curve OID. Tse, et al. Expires June 18, 2018 [Page 16]

Internet-Draft SCA Extensions for OpenPGP December 2017 13. Compatibility Profiles 13.1. SCA SM234 Profile The "SCA SM234" profile is designed to be compliant to SCA regulations. A compliant OpenPGP implementation *MUST* implement the following items as described by this document: o SM2 Recommended Curve (Section 12) o SM2 (SM2DSA and SM2PKE) (Section 4) * The hash function selected in SM2DSA and SM2PKE *MUST* also be SCA-compliant, such as SM3 [SM3] o SM3 (Section 5) o SM4 (Section 6) 14. Security Considerations o Products and services that utilize cryptography are regulated by the SCA [SCA]; they must be explicitly approved or certified by the SCA before being allowed to be sold or used in China. o SM2 [GBT.32918.1-2016] is an elliptic curve cryptosystem (ECC) approved by the SCA [SCA]. Its security relies on the assumption that the elliptic curve discrete logarithm problem (ECLP) is computationally infeasible. With advances in cryptanalysis, new attack algorithms may reduce the complexity of ECLP, making it easier to attack the SM2 cryptosystem that is considered secure at the time this document is published. You *SHOULD* check current literature to determine if the algorithms in SM2 have been found vulnerable. o There are security concerns with regards to side-channel attacks against ECCs, including template attacks (such as [SM2-Template]) that rely on physical access to the computation device. An implementer of ECC systems *SHOULD* be aware of potential vulnerabilities in this regard. o SM3 [GBT.32905-2016] is a cryptographic hash algorithm approved by the SCA [SCA]. Security considerations provided in [I-D.sca-cfrg-sm3] apply. There are no known practical attacks against the SM3 algorithm at the time this document is published. o SM4 [GBT.32907-2016] is a blockcipher approved by the SCA [SCA]. Security considerations of SM4 offered in [I-D.ribose-cfrg-sm4] Tse, et al. Expires June 18, 2018 [Page 17]

Internet-Draft SCA Extensions for OpenPGP December 2017 apply. No formal proof of security is provided but there are no known practical attacks against the SM4 algorithm by the time of publishing this document. There are security concerns with regards to side-channel attacks, when the SM4 algorithm is implemented in a device [SM4-Power]. Side-channel security concerns are described in [I-D.ribose-cfrg-sm4]. When the SM4 algorithm is implemented in hardware, the parameters/keys *SHOULD* be randomly generated without fixed correlation. o SM2 has a key length of 512 bits for the public key and 256 bits for the private key. It is considered an alternative to ECDSA P-256 [RFC6637]. Its security strength is comparable to a 128-bit symmetric key strength [I-D.ietf-msec-mikey-ecc], e.g., AES-128 [NIST.FIPS.197]. o SM3 is a hash function that generates a 256-bit hash value. It is considered as an alternative to SHA-256 [RFC6234]. o SM4 is a blockcipher symmetric algorithm with a key length of 128 bits. It is considered as an alternative to AES-128 [NIST.FIPS.197]. o Security considerations offered in [RFC6637] and [RFC4880] also apply. 15. IANA Considerations The IANA "Pretty Good Privacy (PGP)" registry [RFC8126] has made the following assignments for algorithms described in this document, namely: o ID XXX of the "Public Key Algorithms" namespace for SM2 Section 4 o ID XXX of the "Hash Algorithms" namespace for SM3 Section 5 o ID XXX of the "Symmetric Key Algorithms" namespace for SM4 Section 6 16. References 16.1. Normative References Tse, et al. Expires June 18, 2018 [Page 18]

Internet-Draft SCA Extensions for OpenPGP December 2017 [GBT.32905-2016] Standardization Administration of the People's Republic of China, "GB/T 32905-2016 Information Security Techniques -- SM3 Cryptographic Hash Algorithm", August 2016, <http://www.gb688.cn/bzgk/gb/ newGbInfo?hcno=45B1A67F20F3BF339211C391E9278F5E>. [GBT.32907-2016] Standardization Administration of the People's Republic of China, "GB/T 32907-2016 Information Security Technology -- SM4 Block Cipher Algorithm", August 2016, <http://www.gb688.cn/bzgk/gb/ newGbInfo?hcno=7803DE42D3BC5E80B0C3E5D8E873D56A>. [GBT.32918.2-2016] Standardization Administration of the People's Republic of China, "GB/T 32918.2-2016 Information Security Technology -- Public Key Cryptographic Algorithm SM2 Based On Elliptic Curves -- Part 2: Digital Signature Algorithm", August 2016, <http://www.gb688.cn/bzgk/gb/ newGbInfo?hcno=6F1FAEB62F9668F25F38E0BF0291D4AC>. [GBT.32918.4-2016] Standardization Administration of the People's Republic of China, "GB/T 32918.4-2016 Information Security Technology -- Public Key Cryptographic Algorithm SM2 Based On Elliptic Curves -- Part 4: Public Key Encryption Algorithm", August 2016, <http://www.gb688.cn/bzgk/gb/ newGbInfo?hcno=370AF152CB5CA4A377EB4D1B21DECAE0>. [GBT.32918.5-2017] Standardization Administration of the People's Republic of China, "GB/T 32918.5-2017 Information Security Technology -- Public Key Cryptographic Algorithm SM2 Based On Elliptic Curves -- Part 5: Parameter Definition", May 2017, <http://www.gb688.cn/bzgk/gb/ newGbInfo?hcno=728DEA8B8BB32ACFB6EF4BF449BC3077>. [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>. [RFC4880] Callas, J., Donnerhacke, L., Finney, H., Shaw, D., and R. Thayer, "OpenPGP Message Format", RFC 4880, DOI 10.17487/RFC4880, November 2007, <https://www.rfc-editor.org/info/rfc4880>. Tse, et al. Expires June 18, 2018 [Page 19]

Internet-Draft SCA Extensions for OpenPGP December 2017 [RFC6637] Jivsov, A., "Elliptic Curve Cryptography (ECC) in OpenPGP", RFC 6637, DOI 10.17487/RFC6637, June 2012, <https://www.rfc-editor.org/info/rfc6637>. 16.2. Informative References [BOTAN] Lloyd, J., "Botan: Crypto and TLS for C++11", October 2017, <https://botan.randombit.net>. [GB.15629.11-2003] Standardization Administration of the People's Republic of China, "Information technology -- Telecommunications and information exchange between systems -- Local and metropolitan area networks -- Specific requirements -- Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications", May 2003, <http://www.gb688.cn/bzgk/gb/ newGbInfo?hcno=74B9DD11287E72408C19C4D3A360D1BD>. [GBT.32918.1-2016] Standardization Administration of the People's Republic of China, "GB/T 32918.1-2016 Information Security Technology -- Public Key Cryptographic Algorithm SM2 Based On Elliptic Curves -- Part 1: General", August 2016, <http://www.gb688.cn/bzgk/gb/ newGbInfo?hcno=3EE2FD47B962578070541ED468497C5B>. [GBT.32918.3-2016] Standardization Administration of the People's Republic of China, "GB/T 32918.3-2016 Information Security Technology -- Public Key Cryptographic Algorithm SM2 Based On Elliptic Curves -- Part 3: Key Exchange", August 2016, <http://www.gb688.cn/bzgk/gb/ newGbInfo?hcno=66A89DD6DA64F49C49456B757BA0624F>. [GMT-0002-2012] Office of State Commercial Cryptography Administration of China, "GM/T 0002-2012: SM4 Block Cipher Algorithm", March 2012, <http://www.oscca.gov.cn/Column/Column_32.htm>. [GMT-0003-2012] Office of State Commercial Cryptography Administration of China, "GM/T 0003-2012: Public Key Cryptographic Algorithm SM2 Based on Elliptic Curves", March 2012, <http://www.oscca.gov.cn/Column/Column_32.htm>. Tse, et al. Expires June 18, 2018 [Page 20]

Internet-Draft SCA Extensions for OpenPGP December 2017 [GMT-0004-2012] Office of State Commercial Cryptography Administration of China, "GM/T 0004-2012: SM3 Hash Algorithm", March 2012, <http://www.oscca.gov.cn/Column/Column_32.htm>. [GMT-0006-2012] Office of State Commercial Cryptography Administration of China, "GM/T 0006-2012: Cryptographic Application Identifier Criterion Specification", March 2012, <http://www.oscca.gov.cn/Column/Column_32.htm>. [GMT-0009-2012] Office of State Commercial Cryptography Administration of China, "GM/T 0009-2012: SM2 cryptography algorithm application specification", March 2012, <http://www.oscca.gov.cn/Column/Column_32.htm>. [I-D.ietf-msec-mikey-ecc] Milne, A., "ECC Algorithms for MIKEY", draft-ietf-msec- mikey-ecc-03 (work in progress), June 2007. [I-D.ribose-cfrg-sm4] Tse, R. and W. Wong, "The SM4 Blockcipher Algorithm And Its Modes Of Operations", draft-ribose-cfrg-sm4-08 (work in progress), December 2017. [I-D.sca-cfrg-sm3] Shen, S., Lee, X., Tse, R., Wong, W., and P. Yang, "The SM3 Cryptographic Hash Function", draft-sca-cfrg-sm3-00 (work in progress), December 2017. [I-D.shen-sm2-ecdsa] Shen, S., Shen, S., and X. Lee, "SM2 Digital Signature Algorithm", draft-shen-sm2-ecdsa-02 (work in progress), February 2014. [IEEE.1363a.2004] Institute of Electrical and Electronics Engineers, "IEEE Std 1363a-2004: IEEE Standard Specifications for Public- Key Cryptography -- Amendment 1: Additional Techniques", September 2004, <http://grouper.ieee.org/groups/1363/>. [ISO.IEC.10118-3] International Organization for Standardization, "ISO/IEC FDIS 10118-3 -- Information technology -- Security techniques -- Hash-functions -- Part 3: Dedicated hash- functions", September 2017, <https://www.iso.org/standard/67116.html>. Tse, et al. Expires June 18, 2018 [Page 21]

Internet-Draft SCA Extensions for OpenPGP December 2017 [ISO.IEC.11889] International Organization for Standardization, "ISO/IEC 11889-1:2015 -- Information technology -- Trusted platform module library", August 2015, <https://www.iso.org/standard/66510.html>. [ISO.IEC.14888-3] International Organization for Standardization, "ISO/IEC 14888-3:2016-03 -- Information technology -- Security techniques -- Digital signatures with appendix -- Part 3: Discrete logarithm based mechanisms", September 2017, <https://www.iso.org/standard/70631.html>. [ISO.IEC.18033-3.AMD2] International Organization for Standardization, "ISO/IEC WD1 18033-3/AMD2 -- Information technology -- Security techniques -- Encryption algorithms -- Part 3: Block ciphers -- Amendment 2", June 2017, <https://www.iso.org/standard/54531.html>. [NIST.FIPS.180-4] National Institute of Standards and Technology, "FIPS 180-4 Secure Hash Standard (SHS)", August 2015, <http://dx.doi.org/10.6028/NIST.FIPS.180-4>. [NIST.FIPS.197] National Institute of Standards and Technology, "FIPS 197 Advanced Encryption Standard (AES)", November 2001, <https://doi.org/10.6028/NIST.FIPS.197>. [NIST.SP.800-56Ar2] Barker, B., Chen, L., Roginsky, A., and M. Smid, "SP 800-56Ar2 Recommendation for Pair-Wise Key Establishment Schemes Using Discrete Logarithm Cryptography", May 2013, <http://dx.doi.org/10.6028/NIST.SP.800-56Ar2>. [OSCCA-SM2] Office of State Commercial Cryptography Administration of China, "Public Key Cryptographic Algorithm SM2 Based on Elliptic Curves", December 2010, <http://www.oscca.gov.cn/UpFile/2010122214822692.pdf>. [RFC6150] Turner, S. and L. Chen, "MD4 to Historic Status", RFC 6150, DOI 10.17487/RFC6150, March 2011, <https://www.rfc-editor.org/info/rfc6150>. Tse, et al. Expires June 18, 2018 [Page 22]

Internet-Draft SCA Extensions for OpenPGP December 2017 [RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms (SHA and SHA-based HMAC and HKDF)", RFC 6234, DOI 10.17487/RFC6234, May 2011, <https://www.rfc-editor.org/info/rfc6234>. [RFC7253] Krovetz, T. and P. Rogaway, "The OCB Authenticated- Encryption Algorithm", RFC 7253, DOI 10.17487/RFC7253, May 2014, <https://www.rfc-editor.org/info/rfc7253>. [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, <https://www.rfc-editor.org/info/rfc8126>. [RNP] Ribose Inc., "Botan: Crypto and TLS for C++11", October 2017, <https://open.ribose.com>. [SCA] State Cryptography Administration of China, "State Cryptography Administration of China", Dec 2017, <http://www.sca.gov.cn>. [SEC1] Standards for Efficient Cryptography Group, "SEC 1: Elliptic Curve Cryptography", September 2010, <http://www.secg.org/SEC1-Ver-1.0.pdf>. [SM2-1] Office of State Commercial Cryptography Administration of China, "Public Key Cryptographic Algorithm SM2 Based on Elliptic Curves -- Part 1: General", December 2010, <http://www.oscca.gov.cn/UpFile/2010122214822692.pdf>. [SM2-2] Office of State Commercial Cryptography Administration of China, "Public Key Cryptographic Algorithm SM2 Based on Elliptic Curves -- Part 2: Digital Signature Algorithm", December 2010, <http://www.oscca.gov.cn/UpFile/2010122214822692.pdf>. [SM2-3] Office of State Commercial Cryptography Administration of China, "Public Key Cryptographic Algorithm SM2 Based on Elliptic Curves -- Part 3: Key Exchange Protocol", December 2010, <http://www.oscca.gov.cn/UpFile/2010122214822692.pdf>. [SM2-4] Office of State Commercial Cryptography Administration of China, "Public Key Cryptographic Algorithm SM2 Based on Elliptic Curves -- Part 4: Public Key Encryption Algorithm", December 2010, <http://www.oscca.gov.cn/UpFile/2010122214822692.pdf>. Tse, et al. Expires June 18, 2018 [Page 23]

Internet-Draft SCA Extensions for OpenPGP December 2017 [SM2-5] Office of State Commercial Cryptography Administration of China, "Public Key Cryptographic Algorithm SM2 Based on Elliptic Curves -- Part 5: Parameter definitions", December 2010, <http://www.oscca.gov.cn/UpFile/2010122214836668.pdf>. [SM2-DSA-Lattice] Cao, W., Feng, J., Zhu, S., Chen, H., Wu, W., Han, X., and X. Zheng, "Practical Lattice-Based Fault Attack and Countermeasure on SM2 Signature Algorithm", November 2016, <https://doi.org/10.1007/978-3-319-29814-6_6>. [SM2-DSA-Nonces] Liu, M., Chen, J., and H. Li, "Partially Known Nonces and Fault Injection Attacks on SM2 Signature Algorithm", November 2013, <https://dx.doi.org/10.1007/978-3-319-12087-4_22>. [SM2-DSA-Nonces2] Chen, J., Liu, M., Shi, H., and H. Li, "Mind Your Nonces Moving: Template-Based Partially-Sharing Nonces Attack on SM2 Digital Signature Algorithm", November 2015, <https://doi.acm.org/10.1145/2714576.2714587>. [SM2-KEP-Comments] Xu, X. and D. Feng, "Comments on the SM2 Key Exchange Protocol", December 2011, <https://dx.doi.org/10.1007/978-3-642-25513-7_12>. [SM2-SigSecurity] Zhang, Z., Yang, K., Zhang, J., and C. Chen, "Security of the SM2 Signature Scheme Against Generalized Key Substitution Attacks", December 2015, <https://link.springer.com/ chapter/10.1007/978-3-319-27152-1_7>. [SM2-Template] Zhang, Z., Wu, L., Mu, Z., and X. Zhang, "A Novel Template Attack on wNAF Algorithm of ECC", November 2014, <https://doi.org/10.1109/CIS.2014.66>. [SM3] Office of State Commercial Cryptography Administration of China, "SM3 Cryptographic Hash Algorithm", December 2010, <http://www.oscca.gov.cn/UpFile/20101222141857786.pdf>. Tse, et al. Expires June 18, 2018 [Page 24]

Internet-Draft SCA Extensions for OpenPGP December 2017 [SM3-Boomerang] Bai, D., Yu, H., Wang, G., and X. Wang, "Improved Boomerang Attacks on Round-Reduced SM3 and Keyed Permutation of BLAKE-256", April 2015, <https://doi.org/10.1049/iet-ifs.2013.0380>. [SM4] Office of State Commercial Cryptography Administration of China, "SM4 block cipher algorithm", December 2010, <http://www.oscca.gov.cn/UpFile/200621016423197990.pdf>. [SM4-Power] Du, Z., Wu, Z., Wang, M., and J. Rao, "Improved chosen- plaintext power analysis attack against SM4 at the round- output", October 2015, <https://www.researchgate.net/ publication/285470160_Improved_chosen- plaintext_power_analysis_attack_against_SM4_at_the_round- output>. Appendix A. Examples A.1. Public Key Example This example is generated using the OpenPGP implementation RNP [RNP], with the SM2 and SM3 implementations from Botan [BOTAN]. -----BEGIN PGP PUBLIC KEY BLOCK----- xlIEWbGKWmMIKoEcz1UBgi0CAwQx5lUJNwGp01AB7YfAye0oMmyIPYe/cQPVwh8/7RCu ywZLMDDAM7qn6TNqTtdKW+7tLFhtOC4yzDVK8UjN/ccazSBTTTIgMjU2LWJpdCBrZXkg PGphY2tAbG9jYWxob3N0PsJ0BBNjaQAmBQJZsYpfAhsDBQsJCAcCBhUICQoLAgUWAgMB AAkQC/UcNw0bAZcAAJt5AP4oXvi3xl2RUwAvVjlzXtLL87g6x9cIBS7EB/cvAsw78AEA /Wt6qWlBVZ6TYiqNPt9An/4cjKyNpAv7S9u3neGXWUU= =RJ3C -----END PGP PUBLIC KEY BLOCK----- A.2. Signature Example This example is also created using RNP [RNP] and Botan [BOTAN]. Detached signature of the string "SM2 example" using the above key: -----BEGIN PGP SIGNATURE----- wmQEAGMIABYFAlmxj+cFAwAAAAAJEAv1HDcNGwGXAAB+SQEAy5AHKgiRxgOogB/2sfge JaVoLgpxvDp9yIcaLfP++xkBAPGuZ1f9FjxVd5jlCGd1jFzAPpt8N2Lc3FQDqVjgJvV9 =Xbbj -----END PGP SIGNATURE----- Tse, et al. Expires June 18, 2018 [Page 25]

Internet-Draft SCA Extensions for OpenPGP December 2017 Appendix B. Acknowledgements The authors would like to thank the following persons for their valuable advice and input. o The Ribose RNP team for their input and implementation Authors' Addresses Ronald Henry Tse Ribose Suite 1111, 1 Pedder Street Central, Hong Kong Hong Kong Email: ronald.tse@ribose.com URI: https://www.ribose.com Dr. Wai Kit Wong Hang Seng Management College Hang Shin Link, Siu Lek Yuen Shatin, Hong Kong Hong Kong Email: wongwk@hsmc.edu.hk URI: https://www.hsmc.edu.hk Jack E. Lloyd Ribose United States of America Email: jack.lloyd@ribose.com URI: https://www.ribose.com D. E. Wyatt Ribose 608 W Cork St, Apt 2 Winchester, VA United States of America Email: daniel.wyatt@ribose.com URI: https://www.ribose.com Tse, et al. Expires June 18, 2018 [Page 26]

Internet-Draft SCA Extensions for OpenPGP December 2017 Erick Borsboom Ribose Suite 1111, 1 Pedder Street Central, Hong Kong Hong Kong Email: erick.borsboom@ribose.com URI: https://www.ribose.com Tse, et al. Expires June 18, 2018 [Page 27]