--- 1/draft-ietf-lamps-cms-hash-sig-09.txt 2019-09-18 14:13:10.856380571 -0700 +++ 2/draft-ietf-lamps-cms-hash-sig-10.txt 2019-09-18 14:13:10.888381381 -0700 @@ -1,19 +1,19 @@ INTERNET-DRAFT R. Housley Internet Engineering Task Force (IETF) Vigil Security Intended Status: Proposed Standard -Expires: 10 February 2020 10 August 2019 +Expires: 18 March 2020 18 September 2019 Use of the HSS/LMS Hash-based Signature Algorithm in the Cryptographic Message Syntax (CMS) - + Abstract This document specifies the conventions for using the Hierarchical Signature System (HSS) / Leighton-Micali Signature (LMS) hash-based signature algorithm with the Cryptographic Message Syntax (CMS). In addition, the algorithm identifier and public key syntax are provided. The HSS/LMS algorithm is one form of hash-based digital signature; it is described in RFC 8554. @@ -79,87 +79,84 @@ This document specifies the conventions for using the Hierarchical Signature System (HSS) / Leighton-Micali Signature (LMS) hash-based signature algorithm with the Cryptographic Message Syntax (CMS) [CMS] signed-data content type. The LMS system provides a one-time digital signature that is a variant of Merkle Tree Signatures (MTS). The HSS is built on top of the LMS system to efficiently scale for a larger numbers of signatures. The HSS/LMS algorithm is one form of hash- based digital signature, and it is described in [HASHSIG]. The HSS/LMS signature algorithm can only be used for a fixed number of - signing operations. The number of signing operations depends upon - the size of the tree. The HSS/LMS signature algorithm uses small - public keys, and it has low computational cost; however, the - signatures are quite large. The HSS/LMS private key can be very - small when the signer is willing to perform additional computation at - signing time; alternatively, the private key can consume additional - memory and provide a faster signing time. The HSS/LMS signatures - [HASHSIG] are currently defined to use exclusively SHA-256 [SHS]. + signing operations with a given private key, and the number of + signing operations depends upon the size of the tree. The HSS/LMS + signature algorithm uses small public keys, and it has low + computational cost; however, the signatures are quite large. The + HSS/LMS private key can be very small when the signer is willing to + perform additional computation at signing time; alternatively, the + private key can consume additional memory and provide a faster + signing time. The HSS/LMS signatures [HASHSIG] are currently defined + to use exclusively SHA-256 [SHS]. 1.1. ASN.1 CMS values are generated using ASN.1 [ASN1-B], using the Basic Encoding Rules (BER) and the Distinguished Encoding Rules (DER) [ASN1-E]. 1.2. 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. 1.3. Motivation - There have been recent advances in cryptanalysis and advances in the - development of quantum computers. Each of these advances pose a - threat to widely deployed digital signature algorithms. - - Recent advances in cryptoanalysis [BH2013] and progress in the + Recent advances in cryptanalysis [BH2013] and progress in the development of quantum computers [NAS2019] pose a threat to widely deployed digital signature algorithms. As a result, there is a need to prepare for a day that cryptosystems such as RSA and DSA that depend on discrete logarithm and factoring cannot be depended upon. If large-scale quantum computers are ever built, these computers will be able to break many of the public-key cryptosystems currently in use. A post-quantum cryptosystem [PQC] is a system that is secure against quantum computers that have more than a trivial number of - quantum bits (qu-bits). It is open to conjecture when it will be + quantum bits (qubits). It is open to conjecture when it will be feasible to build such computers; however, RSA, DSA, ECDSA, and EdDSA are all vulnerable if large-scale quantum computers come to pass. - The HSS/LMS signature algorithm does not depend on the difficulty of - discrete logarithm or factoring, as a result these algorithms are - considered to be post-quantum secure. One use of post-quantum secure - signatures is the protection of software updates, perhaps using the - format described in [FWPROT], to enable deployment of software that - implements new cryptosystems. + Since the HSS/LMS signature algorithm does not depend on the + difficulty of discrete logarithm or factoring, the HSS/LMS signature + algorithm is considered to be post-quantum secure. One use of post- + quantum secure signatures is the protection of software updates, + perhaps using the format described in [FWPROT], to enable deployment + of software that implements new cryptosystems. 2. HSS/LMS Hash-based Signature Algorithm Overview Merkle Tree Signatures (MTS) are a method for signing a large but fixed number of messages. An MTS system depends on a one-time signature method and a collision-resistant hash function. This specification makes use of the hash-based algorithm specified in [HASHSIG], which is the Leighton and Micali adaptation [LM] of the original Lamport-Diffie-Winternitz-Merkle one-time signature system [M1979][M1987][M1989a][M1989b]. As implied by the name, the hash-based signature algorithm depends on a collision-resistant hash function. The hash-based signature - algorithm specified in [HASHSIG] currently uses only the SHA-256 one- - way hash function [SHS], but it also establishes an IANA registry - [IANA-LMS] to permit the registration of additional one-way hash - functions in the future. + algorithm specified in [HASHSIG] uses only the SHA-256 one-way hash + function [SHS], but it establishes an IANA registry [IANA-LMS] to + permit the registration of additional one-way hash functions in the + future. 2.1. Hierarchical Signature System (HSS) The MTS system specified in [HASHSIG] uses a hierarchy of trees. The Hierarchical N-time Signature System (HSS) allows subordinate trees to be generated when needed by the signer. Otherwise, generation of the entire tree might take weeks or longer. An HSS signature as specified in [HASHSIG] carries the number of signed public keys (Nspk), followed by that number of signed public @@ -195,22 +192,22 @@ the public key itself. Note that Nspk is the number of levels in the hierarchy of trees minus 1. 2.2. Leighton-Micali Signature (LMS) Each tree in the system specified in [HASHSIG] uses the Leighton- Micali Signature (LMS) system. LMS systems have two parameters. The first parameter is the height of the tree, h, which is the number of levels in the tree minus one. The [HASHSIG] specification supports five values for this parameter: h=5; h=10; h=15; h=20; and h=25. - Note that there are 2^h leaves in the tree. The second parameter is - the number of bytes output by the hash function, m, which is the + Note that there are 2^h leaves in the tree. The second parameter, m, + is the number of bytes output by the hash function, and it is the amount of data associated with each node in the tree. The [HASHSIG] specification supports only the SHA-256 hash function [SHS], with m=32. As a result, the [HASHSIG] specification supports five tree sizes; they are identified as: LMS_SHA256_M32_H5; LMS_SHA256_M32_H10; LMS_SHA256_M32_H15; LMS_SHA256_M32_H20; and LMS_SHA256_M32_H25. @@ -298,29 +295,31 @@ The algorithm identifier for an HSS/LMS hash-based signatures is: id-alg-hss-lms-hashsig OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) alg(3) 17 } When this object identifier is used for an HSS/LMS signature, the AlgorithmIdentifier parameters field MUST be absent (that is, the parameters are not present; the parameters are not set to NULL). - The signature value is a large OCTET STRING. The signature format is - designed for easy parsing. Each format includes a counter and type - codes that indirectly providing all of the information that is needed - to parse the value during signature validation. + The signature value is a large OCTET STRING as described in Section 2 + of this document. The signature format is designed for easy parsing. + The HSS, LMS, and LMOTS component of the signature value each format + include a counter and a type code that indirectly provide all of the + information that is needed to parse the value during signature + validation. The signature value identifies the hash function used in the HSS/LMS - tree. In [HASHSIG] only the SHA-256 hash function [SHS] is - supported, but it also establishes an IANA registry [IANA-LMS] to - permit the registration of additional hash functions in the future. + tree. In [HASHSIG] uses only the SHA-256 hash function [SHS], but it + establishes an IANA registry [IANA-LMS] to permit the registration of + additional hash functions in the future. 4. HSS/LMS Public Key Identifier The AlgorithmIdentifier for an HSS/LMS public key uses the id-alg- hss-lms-hashsig object identifier, and the parameters field MUST be absent. When this AlgorithmIdentifier appears in the SubjectPublicKeyInfo field of an X.509 certificate [RFC5280], the certificate key usage extension MAY contain digitalSignature, nonRepudiation, keyCertSign, @@ -337,57 +336,56 @@ Note that the id-alg-hss-lms-hashsig algorithm identifier is also referred to as id-alg-mts-hashsig. This synonym is based on the terminology used in an early draft of the document that became [HASHSIG]. The public key value is an OCTET STRING. Like the signature format, it is designed for easy parsing. The value is the number of levels in the public key, L, followed by the LMS public key. - The HSS/LMS public key value can be summarized as: + The HSS/LMS public key value can be described as: u32str(L) || lms_public_key Note that the public key for the top-most LMS tree is the public key of the HSS system. When L=1, the HSS system is a single tree. 5. Signed-data Conventions As specified in [CMS], the digital signature is produced from the message digest and the signer's private key. The signature is computed over different values depending on whether signed attributes are absent or present. When signed attributes are absent, the HSS/LMS signature is computed over the content. When signed attributes are present, a hash is computed over the content using the same hash function that is used in the HSS/LMS tree, and then a message-digest attribute is - constructed to contain the resulting hash value, and then the result - of DER encoding the set of signed attributes (which MUST include a - content-type attribute and a message-digest attribute, and then the - HSS/LMS signature is computed over the DER-encoded output. In - summary: + constructed with the hash of the content, and then the HSS/LMS + signature is computed over the DER-encoded set of signed attributes + (which MUST include a content-type attribute and a message-digest + attribute). In summary: IF (signed attributes are absent) THEN HSS_LMS_Sign(content) ELSE message-digest attribute = Hash(content); HSS_LMS_Sign(DER(SignedAttributes)) When using [HASHSIG], the fields in the SignerInfo are used as follows: - digestAlgorithm MUST contain the one-way hash function used to in - the HSS/LMS tree. In [HASHSIG], SHA-256 is the only supported - hash function, but other hash functions might be registered in - the future. For convenience, the AlgorithmIdentifier for - SHA-256 from [PKIXASN1] is repeated here: + digestAlgorithm MUST contain the one-way hash function used in the + HSS/LMS tree. In [HASHSIG], SHA-256 is the only supported hash + function, but other hash functions might be registered in the + future. For convenience, the AlgorithmIdentifier for SHA-256 + from [PKIXASN1] is repeated here: mda-sha256 DIGEST-ALGORITHM ::= { IDENTIFIER id-sha256 PARAMS TYPE NULL ARE preferredAbsent } id-sha256 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) gov(101) csor(3) nistAlgorithms(4) hashalgs(2) 1 } signatureAlgorithm MUST contain id-alg-hss-lms-hashsig, and the @@ -397,43 +395,45 @@ the signing operation as specified in [HASHSIG]. 6. Security Considerations Implementations MUST protect the private keys. Compromise of the private keys may result in the ability to forge signatures. Along with the private key, the implementation MUST keep track of which leaf nodes in the tree have been used. Loss of integrity of this tracking data can cause a one-time key to be used more than once. As a result, when a private key and the tracking data are stored on non- - volatile media or stored in a virtual machine environment, care must - be taken to preserve confidentiality and integrity. + volatile media or stored in a virtual machine environment, failed + writes, virtual machine snapshotting or cloning, and other + operational concerns must be considered to ensure confidentiality and + integrity. When generating an LMS key pair, an implementation MUST generate each key pair independently of all other key pairs in the HSS tree. An implementation MUST ensure that a LM-OTS private key is used to generate a signature only one time, and ensure that it cannot be used for any other purpose. The generation of private keys relies on random numbers. The use of inadequate pseudo-random number generators (PRNGs) to generate these values can result in little or no security. An attacker may find it much easier to reproduce the PRNG environment that produced the keys, searching the resulting small set of possibilities, rather than brute force searching the whole key space. The generation of quality random numbers is difficult, and [RFC4086] offers important guidance in this area. The generation of hash-based signatures also depends on random numbers. While the consequences of an inadequate pseudo-random - number generator (PRNGs) to generate these values is much less severe - than the generation of private keys, the guidance in [RFC4086] + number generator (PRNG) to generate these values is much less severe + than in the generation of private keys, the guidance in [RFC4086] remains important. When computing signatures, the same hash function SHOULD be used to compute the message digest of the content and the signed attributes, if they are present. 7. IANA Considerations SMI Security for S/MIME Module Identifier (1.2.840.113549.1.9.16.0) registry, change the reference for value 64 to point to this @@ -615,24 +615,24 @@ SMimeCaps SMIME-CAPS ::= { sa-HSS-LMS-HashSig.&smimeCaps, ... } END Acknowledgements - Many thanks to Scott Fluhrer, Jonathan Hammell, Panos Kampanakis, - John Mattsson, Jim Schaad, Sean Turner, Daniel Van Geest, Roman - Danyliw, Dale Worley, and Joe Clarke for their careful review and - comments. + Many thanks to Scott Fluhrer, Jonathan Hammell, Ben Kaduk, Panos + Kampanakis, Barry Leiba, John Mattsson, Jim Schaad, Sean Turner, + Daniel Van Geest, Roman Danyliw, Dale Worley, and Joe Clarke for + their careful review and comments. Author's Address Russ Housley Vigil Security, LLC 516 Dranesville Road Herndon, VA 20170 USA EMail: housley@vigilsec.com