Network Working Group R. Housley Internet-Draft Vigil Security Updates: 4211 (if approved) 30 March 2021 Intended status: Standards Track Expires: 1 October 2021 Algorithm Requirements Update to the Internet X.509 Public Key Infrastructure Certificate Request Message Format (CRMF) draft-ietf-lamps-crmf-update-algs-05 Abstract This document updates the cryptographic algorithm requirements for the Password-Based Message Authentication Code in the Internet X.509 Public Key Infrastructure Certificate Request Message Format (CRMF) specified in RFC 4211. 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/. 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Housley Expires 1 October 2021 [Page 1] Internet-Draft CRMF Algorithm Requirements Update March 2021 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Signature Key POP . . . . . . . . . . . . . . . . . . . . . . 3 4. Password-Based Message Authentication Code . . . . . . . . . 3 4.1. Introduction Paragraph . . . . . . . . . . . . . . . . . 3 4.2. One-Way Function . . . . . . . . . . . . . . . . . . . . 4 4.3. Iteration Count . . . . . . . . . . . . . . . . . . . . . 4 4.4. MAC Algorithm . . . . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 8.1. Normative References . . . . . . . . . . . . . . . . . . 7 8.2. Informative References . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction This document updates the cryptographic algorithm requirements for the Password-Based Message Authentication Code (MAC) in the Internet X.509 Public Key Infrastructure Certificate Request Message Format (CRMF) [RFC4211]. The algorithms specified in [RFC4211] were appropriate in 2005; however, these algorithms are no longer considered the best choices: * HMAC-SHA1 [HMAC][SHS] is not boken yet, but there are much stronger alternatives [RFC6194]. * DES-MAC [PKCS11] provides 56 bits of security, which is no longer considered secure [WITHDRAW]. * Triple-DES-MAC [PKCS11] provides 112 bits of security, which is now deprecated [TRANSIT]. This update specifies algorithms that are more appropriate today. 2. Terminology 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. Housley Expires 1 October 2021 [Page 2] Internet-Draft CRMF Algorithm Requirements Update March 2021 3. Signature Key POP Section 4.1 of [RFC4211] specifies the Proof-of-Possession (POP) processing. This section is updated to explicitly allow the use of the PBMAC1 algorithm presented in Section 7.1 of [RFC8018]. OLD: algId identifies the algorithm used to compute the MAC value. All implementations MUST support id-PasswordBasedMAC. The details on this algorithm are presented in section 4.4 NEW: algId identifies the algorithm used to compute the MAC value. All implementations MUST support id-PasswordBasedMAC as presented in Section 4.4 of [RFC4211]. Implementations MAY also support PBMAC1 presented in Section 7.1 of [RFC8018]. 4. Password-Based Message Authentication Code Section 4.4 of [RFC4211] specifies a Password-Based MAC that relies on a one-way function to compute a symmetric key from the password and a MAC algorithm. This section specifies algorithm requirements for the one-way function and the MAC algorithm. 4.1. Introduction Paragraph Add guidance about limiting the use of the password. OLD: This MAC algorithm was designed to take a shared secret (a password) and use it to compute a check value over a piece of information. The assumption is that, without the password, the correct check value cannot be computed. The algorithm computes the one-way function multiple times in order to slow down any dictionary attacks against the password value. NEW: This MAC algorithm was designed to take a shared secret (a password) and use it to compute a check value over a piece of information. The assumption is that, without the password, the correct check value cannot be computed. The algorithm computes the one-way function multiple times in order to slow down any dictionary attacks against the password value. The password used to compute this MAC SHOULD NOT be used for any other purpose. Housley Expires 1 October 2021 [Page 3] Internet-Draft CRMF Algorithm Requirements Update March 2021 4.2. One-Way Function Change the paragraph describing the "owf" as follows: OLD: owf identifies the algorithm and associated parameters used to compute the key used in the MAC process. All implementations MUST support SHA-1. NEW: owf identifies the algorithm and associated parameters used to compute the key used in the MAC process. All implementations MUST support SHA-256 [SHS]. 4.3. Iteration Count Update the guidance on appropriate iteration count values. OLD: iterationCount identifies the number of times the hash is applied during the key computation process. The iterationCount MUST be a minimum of 100. Many people suggest using values as high as 1000 iterations as the minimum value. The trade off here is between protection of the password from attacks and the time spent by the server processing all of the different iterations in deriving passwords. Hashing is generally considered a cheap operation but this may not be true with all hash functions in the future. NEW: iterationCount identifies the number of times the hash is applied during the key computation process. The iterationCount MUST be a minimum of 100; however, the iterationCount SHOULD be as large as server performance will allow, typically at least 10,000 [DIGALM]. There is a trade off between protection of the password from attacks and the time spent by the server processing the iterations. As part of that tradeoff, an iteration count smaller than 10,000 can be used when automated generation produces shared secrets with high entropy. 4.4. MAC Algorithm Change the paragraph describing the "mac" as follows: OLD: Housley Expires 1 October 2021 [Page 4] Internet-Draft CRMF Algorithm Requirements Update March 2021 mac identifies the algorithm and associated parameters of the MAC function to be used. All implementations MUST support HMAC-SHA1 [HMAC]. All implementations SHOULD support DES-MAC and Triple- DES-MAC [PKCS11]. NEW: mac identifies the algorithm and associated parameters of the MAC function to be used. All implementations MUST support HMAC-SHA256 [HMAC]. All implementations SHOULD support AES-GMAC AES [GMAC] with a 128 bit key. For convenience, the identifiers for these two algorithms are repeated here. The algorithm identifier for HMAC-SHA256 is defined in [RFC4231]: id-hmacWithSHA256 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) digestAlgorithm(2) 9 } When this algorithm identifier is used, the parameters SHOULD be present. When present, the parameters MUST contain a type of NULL. The algorithm identifier for AES-GMAC [AES][GMAC] with a 128-bit key is defined in [I-D.ietf-lamps-cms-aes-gmac-alg]: id-aes128-GMAC OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) gov(101) csor(3) nistAlgorithm(4) aes(1) 9 } When this algorithm identifier is used, the parameters MUST be present, and the parameters MUST contain the GMACParameters structure as follows: GMACParameters ::= SEQUENCE { nonce OCTET STRING, length MACLength DEFAULT 12 } MACLength ::= INTEGER (12 | 13 | 14 | 15 | 16) The GMACParameters nonce parameter is the GMAC initialization vector. The nonce may have any number of bits between 8 and (2^64)-1, but it MUST be a multiple of 8 bits. Within the scope of any GMAC key, the nonce value MUST be unique. A nonce value of 12 octets can be processed more efficiently, so that length for the nonce value is RECOMMENDED. Housley Expires 1 October 2021 [Page 5] Internet-Draft CRMF Algorithm Requirements Update March 2021 The GMACParameters length parameter field tells the size of the message authentication code in octets. GMAC supports lengths between 12 and 16 octets, inclusive. However, for use with CRMF, the maximum length of 16 octets MUST be used. 5. IANA Considerations This document makes no requests of the IANA. 6. Security Considerations The security of the password-based MAC relies on the number of times the hash function is applied as well as the entropy of the shared secret (the password). Hardware support for hash calculation is available at very low cost [PHS], which reduces the protection provided by a high iterationCount value. Therefore, the entropy of the password is crucial for the security of the password-based MAC function. In 2010, researchers showed that about half of the real- world passwords can be broken with less than 150 million trials, indicating a median entropy of only 27 bits [DMR]. Higher entropy can be achieved by using randomly generated strings. For example, assuming an alphabet of 60 characters a randomly chosen password with 10 characters offers 59 bits a entropy, and 20 characters offers 118 bits of entropy. Using a one-time password also increases the security of the MAC, assuming that the integrity-protected transaction will complete before the attacker is able to learn the password with an offline attack. Please see [RFC8018] for security considerations related to PBMAC1. Please see [HMAC] and [SHS] for security considerations related to HMAC-SHA256. Please see [AES] and [GMAC] for security considerations related to AES-GMAC. Cryptographic algorithms age; they become weaker with time. As new cryptanalysis techniques are developed and computing capabilities improve, the work required to break a particular cryptographic algorithm will reduce, making an attack on the algorithm more feasible for more attackers. While it is unknown how cryptoanalytic attacks will evolve, it is certain that they will get better. It is unknown how much better they will become or when the advances will happen. For this reason, the algorithm requirements for CRMF are updated by this specification. Housley Expires 1 October 2021 [Page 6] Internet-Draft CRMF Algorithm Requirements Update March 2021 When a Password-Based MAC is used, implementations must protect the password and the MAC key. Compromise of either the password or the MAC key may result in the ability of an attacker to undermine authentication. 7. Acknowledgements Many thanks to Hans Aschauer, Hendrik Brockhaus, Quynh Dang, Roman Danyliw, Tomas Gustavsson, Jonathan Hammell, Tim Hollebeek, Lijun Liao, Mike Ounsworth, Tim Polk, Ines Robles, Mike StJohns, and Sean Turner for their careful review and improvements. 8. References 8.1. Normative References [AES] National Institute of Standards and Technology, "Advanced encryption standard (AES)", DOI 10.6028/nist.fips.197, November 2001, . [GMAC] National Institute of Standards and Technology, "Recommendation for block cipher modes of operation: Galois Counter Mode (GCM) and GMAC", DOI 10.6028/nist.sp.800-38d, 2007, . [HMAC] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- Hashing for Message Authentication", RFC 2104, DOI 10.17487/RFC2104, February 1997, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC4211] Schaad, J., "Internet X.509 Public Key Infrastructure Certificate Request Message Format (CRMF)", RFC 4211, DOI 10.17487/RFC4211, September 2005, . [RFC8018] Moriarty, K., Ed., Kaliski, B., and A. Rusch, "PKCS #5: Password-Based Cryptography Specification Version 2.1", RFC 8018, DOI 10.17487/RFC8018, January 2017, . Housley Expires 1 October 2021 [Page 7] Internet-Draft CRMF Algorithm Requirements Update March 2021 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [SHS] National Institute of Standards and Technology, "Secure Hash Standard", DOI 10.6028/nist.fips.180-4, July 2015, . 8.2. Informative References [DIGALM] National Institute of Standards and Technology, "Digital identity guidelines: authentication and lifecycle management", DOI 10.6028/nist.sp.800-63b, June 2017, . [DMR] Dell'Amico, M., Michiardi, P., and Y. Roudier, "Password Strength: An Empirical Analysis", DOI 10.1109/INFCOM.2010.5461951, March 2010, . [I-D.ietf-lamps-cms-aes-gmac-alg] Housley, R., "Using the AES-GMAC Algorithm with the Cryptographic Message Syntax (CMS)", Work in Progress, Internet-Draft, draft-ietf-lamps-cms-aes-gmac-alg-02, 30 December 2020, . [PHS] Pathirana, A., Halgamuge, M., and A. Syed, "Energy efficient bitcoin mining to maximize the mining profit: Using data from 119 bitcoin mining hardware setups", International Conference on Advances in Business Management and Information Technology, pp 1-14, November 2019. [PKCS11] RSA Laboratories, "The Public-Key Cryptography Standards - PKCS #11 v2.11: Cryptographic Token Interface Standard", June 2001. [RFC4231] Nystrom, M., "Identifiers and Test Vectors for HMAC-SHA- 224, HMAC-SHA-256, HMAC-SHA-384, and HMAC-SHA-512", RFC 4231, DOI 10.17487/RFC4231, December 2005, . [RFC6194] Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security Considerations for the SHA-0 and SHA-1 Message-Digest Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011, . Housley Expires 1 October 2021 [Page 8] Internet-Draft CRMF Algorithm Requirements Update March 2021 [TRANSIT] National Institute of Standards and Technology, "Transitioning the use of cryptographic algorithms and key lengths", NIST SP 800-131Ar2, March 2019. [WITHDRAW] National Institute of Standards and Technology, "NIST Withdraws Outdated Data Encryption Standard", 2 June 2005. Author's Address Russ Housley Vigil Security, LLC 516 Dranesville Road Herndon, VA, 20170 United States of America Email: housley@vigilsec.com Housley Expires 1 October 2021 [Page 9]