< draft-ietf-dnsext-rsa-02.txt		draft-ietf-dnsext-rsa-03.txt >
	INTERNET-DRAFT RSA SIGs and KEYs in the DNS		A new Request for Comments is now available in online RFC libraries.
	OBSOLETES RFC 2537 December 2000
	Expires June 2001
	D. Eastlake
	RSA/SHA-1 SIGs and RSA KEYs in the Domain Name System (DNS)
	--------- ---- --- --- ---- -- --- ------ ---- ------ -----
	<draft-ietf-dnsext-rsa-02.txt>
	Status of This Document
	This draft is intended to be become a Proposed Standard RFC.
	Distribution of this document is unlimited. Comments should be sent
	to the DNS extensions mailing list <namedroppers@ops.ietf.org> or to
	the author.
	This document is an Internet-Draft and is in full conformance with
	all provisions of Section 10 of RFC 2026. Internet-Drafts are
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	Abstract
	Since the adoption of a Proposed Standard for RSA signatures in the
	DNS [RFC 2537], advances in hashing have been made. A new DNS
	signature algorithm is defined to make these advances available in
	SIG resource records (RRs). The use of the previously specified
	weaker mechanism is deprecated. The algorithm number of the RSA KEY
	RR is changed to correspond to this new SIG algorithm. No other
	changes are made to DNS security.
	INTERNET-DRAFT RSA/SHA1 in the DNS
	Acknowledgements
	Material and comments from the following have been incorporated and
	are gratefully acknowledged:
	Olafur Gudmundsson
	Charlie Kaufman
	Steve Wang
	Table of Contents
	Status of This Document....................................1
	Abstract...................................................1
	Acknowledgements...........................................2
	Table of Contents..........................................2
	1. Introduction............................................3
	2. RSA Public KEY Resource Records.........................3
	3. RSA/SHA1 SIG Resource Records...........................4
	4. Performance Considerations..............................5
	5. IANA Considerations.....................................5
	6. Security Considerations.................................6
	References.................................................7
	Author's Address...........................................8
	Expiration and File Name...................................8
	INTERNET-DRAFT RSA/SHA1 in the DNS
	1. Introduction
	The Domain Name System (DNS) is the global hierarchical replicated
	distributed database system for Internet addressing, mail proxy, and
	other information [RFC 1034, 1035, etc.]. The DNS has been extended
	to include digital signatures and cryptographic keys as described in
	[RFC 2535]. Thus the DNS can now be secured and used for secure key
	distribution.
	Familiarity with the RSA and SHA-1 algorithms is assumed [Schneier,
	FIP180] in this document.
	[RFC 2537] described how to store RSA keys and RSA/MD5 based
	signatures in the DNS. However, since the adoption of [RFC 2537],
	continued cryptographic research has revealed hints of weakness in
	the MD5 [RFC 1321] algorithm used in [RFC 2537]. The SHA1 Secure Hash
	Algorithm [FIP180], which produces a larger hash, has been developed.
	By now there has been sufficient experience with SHA1 that it is
	generally acknowledged to be stronger than MD5. While this stronger
	hash is probably not needed today in most secure DNS zones, critical
	zones such a root and most TLDs are sufficiently valuable targets
	that it would be negligent not to provide what are generally agreed
	to be stronger mechanisms. Furthermore, future advances in
	cryptanalysis and/or computer speeds may require a stronger hash
	everywhere. In addition, the additional computation required by SHA1
	above that required by MD5 is insignificant compared with the
	computational effort required by the RSA modular exponentiation.
	This document describes how to produce RSA/SHA1 SIG RRs in Section 3
	and, so as to completely replace [RFC 2537], describes how to produce
	RSA KEY RRs in Section 2.
	Implementation of the RSA algorithm in DNS with SHA1 is MANDATORY for
	DNSSEC. The generation of RSA/MD5 SIG RRs as described in [RFC 2537]
	is NOT RECOMMENDED.
	The key words "MUST", "REQUIRED", "SHOULD", "RECOMMENDED", "NOT
	RECOMMENDED", and "MAY" in this document are to be interpreted as
	described in [RFC 2119].
	2. RSA Public KEY Resource Records
	RSA public keys are stored in the DNS as KEY RRs using algorithm
	number (TBD, suggest 5) [RFC 2535]. The structure of the algorithm
	specific portion of the RDATA part of such RRs is as shown below.
	INTERNET-DRAFT RSA/SHA1 in the DNS
	Field Size
	----- ----
	exponent length 1 or 3 octets (see text)
	exponent as specified by length field
	modulus remaining space
	For interoperability, the exponent and modulus are each limited to
	4096 bits in length. The public key exponent is a variable length
	unsigned integer. Its length in octets is represented as one octet
	if it is in the range of 1 to 255 and by a zero octet followed by a
	two octet unsigned length if it is longer than 255 bytes. The public
	key modulus field is a multiprecision unsigned integer. The length
	of the modulus can be determined from the RDLENGTH and the preceding
	RDATA fields including the exponent. Leading zero octets are
	prohibited in the exponent and modulus.
	Note: KEY RRs for use with RSA/SHA1 DNS signatures MUST use this
	algorithm number (rather than the algorithm number specified in the
	obsoleted [RFC 2537]).
	Note: This changes the algorithm number for RSA KEY RRs to be the
	same as the new algorithm number for RSA/SHA1 SIGs.
	3. RSA/SHA1 SIG Resource Records
	RSA/SHA1 signatures are stored in the DNS using SIG resource records
	(RRs) with algorithm number (TBD, 5 suggested).
	The signature portion of the SIG RR RDATA area, when using the
	RSA/SHA1 algorithm, is calculated as shown below. The data signed is
	determined as specified in [RFC 2535]. See [RFC 2535] for fields in
	the SIG RR RDATA which precede the signature itself.
	hash = SHA1 ( data )
	signature = ( 01 | FF* | 00 | prefix | hash ) ** e (mod n)
	where SHA1 is the message digest algorithm documented in [FIP180],
	"|" is concatenation, "e" is the private key exponent of the signer,
	and "n" is the modulus of the signer's public key. 01, FF, and 00
	are fixed octets of the corresponding hexadecimal value. "prefix" is
	the ASN.1 BER SHA1 algorithm designator prefix required in PKCS1 [RFC
	2437], that is,
	hex 30 21 30 09 06 05 2B 0E 03 02 1A 05 00 04 14
	This prefix is included to make it easier to use standard
	cryptographic libraries. The FF octet MUST be repeated the maximum
	INTERNET-DRAFT RSA/SHA1 in the DNS
	number of times such that the value of the quantity being
	exponentiated is one octet shorter than the value of n.
	(The above specifications are identical to the corresponding part of
	Public Key Cryptographic Standard #1 [RFC 2437].)
	The size of "n", including most and least significant bits (which
	will be 1) MUST be not less than 512 bits and not more than 4096
	bits. "n" and "e" SHOULD be chosen such that the public exponent is
	small. These are protocol limits. For a discussion of key size see
	[RFC 2541].
	Leading zero bytes are permitted in the RSA/SHA1 algorithm signature.
	A public exponent of 3 minimizes the effort needed to verify a
	signature. Use of 3 as the public exponent is weak for
	confidentiality uses since, if the same data can be collected
	encrypted under three different keys with an exponent of 3 then,
	using the Chinese Remainder Theorem [NETSEC], the original plain text
	can be easily recovered. This weakness is not significant for DNS
	security because we seek only authentication, not confidentiality.
	4. Performance Considerations
	General signature generation speeds are roughly the same for RSA and
	DSA [RFC 2536]. With sufficient pre-computation, signature
	generation with DSA is faster than RSA. Key generation is also
	faster for DSA. However, signature verification is an order of
	magnitude slower with DSA when the RSA public exponent is chosen to
	be small as is recommended for KEY RRs used in domain name system
	(DNS) data authentication.
	Current DNS implementations are optimized for small transfers,
	typically less than 512 bytes including DNS overhead. Larger
	transfers will perform correctly and extensions have been
	standardized [RFC 2671] to make larger transfers more efficient, it
	is still advisable at this time to make reasonable efforts to
	minimize the size of KEY RR sets stored within the DNS consistent
	with adequate security. Keep in mind that in a secure zone, at least
	one authenticating SIG RR will also be returned.
	5. IANA Considerations
	The DNSSEC algorithm number (TBD, 5 suggested) is allocated for
	RSA/SHA1 SIG RRs and RSA KEY RRs.
	INTERNET-DRAFT RSA/SHA1 in the DNS
	6. Security Considerations
	Many of the general security consideration in [RFC 2535] apply. Keys
	retrieved from the DNS should not be trusted unless (1) they have
	been securely obtained from a secure resolver or independently
	verified by the user and (2) this secure resolver and secure
	obtainment or independent verification conform to security policies
	acceptable to the user. As with all cryptographic algorithms,
	evaluating the necessary strength of the key is essential and
	dependent on local policy. For particularly critical applications,
	implementers are encouraged to consider the range of available
	algorithms and key sizes. See also [RFC 2541], "DNS Security
	Operational Considerations".
	INTERNET-DRAFT RSA/SHA1 in the DNS
	References
	[FIP180] - U.S. Department of Commerce, "Secure Hash Standard", FIPS
	PUB 180-1, 17 Apr 1995.
	[NETSEC] - Network Security: PRIVATE Communications in a PUBLIC
	World, Charlie Kaufman, Radia Perlman, & Mike Speciner, Prentice Hall
	Series in Computer Networking and Distributed Communications, 1995.
	[RFC 1034] - P. Mockapetris, "Domain names - concepts and
	facilities", 11/01/1987.
	[RFC 1035] - P. Mockapetris, "Domain names - implementation and
	specification", 11/01/1987.
	[RFC 1321] - R. Rivest, "The MD5 Message-Digest Algorithm", April
	1992.
	[RFC 2119] - S. Bradner, "Key words for use in RFCs to Indicate
	Requirement Levels", March 1997.
	[RFC 2437] - B. Kaliski, J. Staddon, "PKCS #1: RSA Cryptography		RFC 3110
	Specifications Version 2.0", October 1998.
	[RFC 2535] - D. Eastlake, "Domain Name System Security Extensions",		Title: RSA/SHA-1 SIGs and RSA KEYs in the Domain Name
	March 1999.		System (DNS)
			Author(s): D. Eastlake 3rd
			Status: Standards Track
			Date: May 2001
			Mailbox: Donald.Eastlake@motorola.com
			Pages: 7
			Characters: 14587
			Updates/Obsoletes/SeeAlso: None
	[RFC 2536] - D. Eastlake, "DSA KEYs and SIGs in the Domain Name		I-D Tag: draft-ietf-dnsext-rsa-03.txt
	System (DNS)", March 1999.
	[RFC 2537] - D. Eastlake, "RSA/MD5 KEYs and SIGs in the Domain Name		URL: ftp://ftp.rfc-editor.org/in-notes/rfc3110.txt
	System (DNS)", March 1999.
	[RDC 2541] - D. Eastlake, "DNS Security Operational Considerations",		This document describes how to produce RSA/SHA1 SIG resource records
	March 1999.		(RRs) in Section 3 and, so as to completely replace RFC 2537,
			describes how to produce RSA KEY RRs in Section 2.
	[RFC 2671] - P. Vixie, "Extension Mechanisms for DNS (EDNS0)", August		Since the adoption of a Proposed Standard for RSA signatures in the
	1999.		DNS (Domain Name Space), advances in hashing have been made. A new
			DNS signature algorithm is defined to make these advances available in
			SIG RRs. The use of the previously specified weaker mechanism is
			deprecated. The algorithm number of the RSA KEY RR is changed to
			correspond to this new SIG algorithm. No other changes are made to
			DNS security.
	[Schneier] - Bruce Schneier, "Applied Cryptography Second Edition:		This document is a product of the DNS Extensions Working Group of the
	protocols, algorithms, and source code in C", 1996, John Wiley and		IETF.
	Sons, ISBN 0-471-11709-9.
	INTERNET-DRAFT RSA/SHA1 in the DNS		This is now a Proposed Standard Protocol.
	Author's Address		This document specifies an Internet standards track protocol for
			the Internet community, and requests discussion and suggestions
			for improvements. Please refer to the current edition of the
			"Internet Official Protocol Standards" (STD 1) for the
			standardization state and status of this protocol. Distribution
			of this memo is unlimited.
	Donald E. Eastlake 3rd		This announcement is sent to the IETF list and the RFC-DIST list.
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