draft-ietf-dnsext-rsa-02.txt   draft-ietf-dnsext-rsa-03.txt 
INTERNET-DRAFT RSA SIGs and KEYs in the DNS INTERNET-DRAFT RSA SIGs and KEYs in the DNS
OBSOLETES RFC 2537 December 2000 OBSOLETES RFC 2537 April 2001
Expires June 2001 Expires October 2001
D. Eastlake
RSA/SHA-1 SIGs and RSA KEYs in the Domain Name System (DNS) RSA/SHA-1 SIGs and RSA KEYs in the Domain Name System (DNS)
--------- ---- --- --- ---- -- --- ------ ---- ------ ----- --------- ---- --- --- ---- -- --- ------ ---- ------ -----
<draft-ietf-dnsext-rsa-02.txt> <draft-ietf-dnsext-rsa-03.txt>
Donald Eastlake
Status of This Document Status of This Document
This draft is intended to be become a Proposed Standard RFC. This draft is intended to be become a Proposed Standard RFC.
Distribution of this document is unlimited. Comments should be sent Distribution of this document is unlimited. Comments should be sent
to the DNS extensions mailing list <namedroppers@ops.ietf.org> or to to the DNS extensions mailing list <namedroppers@ops.ietf.org> or to
the author. the author.
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026. Internet-Drafts are all provisions of Section 10 of RFC 2026. Internet-Drafts are
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INTERNET-DRAFT RSA/SHA1 in the DNS INTERNET-DRAFT RSA/SHA1 in the DNS
Acknowledgements Acknowledgements
Material and comments from the following have been incorporated and Material and comments from the following have been incorporated and
are gratefully acknowledged: are gratefully acknowledged:
Olafur Gudmundsson Olafur Gudmundsson
The IESG
Charlie Kaufman Charlie Kaufman
Steve Wang Steve Wang
Table of Contents Table of Contents
Status of This Document....................................1 Status of This Document....................................1
Abstract...................................................1 Abstract...................................................1
Acknowledgements...........................................2 Acknowledgements...........................................2
Table of Contents..........................................2 Table of Contents..........................................2
1. Introduction............................................3 1. Introduction............................................3
2. RSA Public KEY Resource Records.........................3 2. RSA Public KEY Resource Records.........................3
3. RSA/SHA1 SIG Resource Records...........................4 3. RSA/SHA1 SIG Resource Records...........................4
4. Performance Considerations..............................5 4. Performance Considerations..............................5
5. IANA Considerations.....................................5 5. IANA Considerations.....................................6
6. Security Considerations.................................6 6. Security Considerations.................................6
References.................................................7 References.................................................7
Author's Address...........................................8 Author's Address...........................................8
Expiration and File Name...................................8 Expiration and File Name...................................8
INTERNET-DRAFT RSA/SHA1 in the DNS INTERNET-DRAFT RSA/SHA1 in the DNS
1. Introduction 1. Introduction
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FIP180] in this document. FIP180] in this document.
[RFC 2537] described how to store RSA keys and RSA/MD5 based [RFC 2537] described how to store RSA keys and RSA/MD5 based
signatures in the DNS. However, since the adoption of [RFC 2537], signatures in the DNS. However, since the adoption of [RFC 2537],
continued cryptographic research has revealed hints of weakness in continued cryptographic research has revealed hints of weakness in
the MD5 [RFC 1321] algorithm used in [RFC 2537]. The SHA1 Secure Hash the MD5 [RFC 1321] algorithm used in [RFC 2537]. The SHA1 Secure Hash
Algorithm [FIP180], which produces a larger hash, has been developed. Algorithm [FIP180], which produces a larger hash, has been developed.
By now there has been sufficient experience with SHA1 that it is By now there has been sufficient experience with SHA1 that it is
generally acknowledged to be stronger than MD5. While this stronger generally acknowledged to be stronger than MD5. While this stronger
hash is probably not needed today in most secure DNS zones, critical hash is probably not needed today in most secure DNS zones, critical
zones such a root and most TLDs are sufficiently valuable targets zones such a root, most top level domains, and some second and third
that it would be negligent not to provide what are generally agreed level domains, are sufficiently valuable targets that it would be
to be stronger mechanisms. Furthermore, future advances in negligent not to provide what are generally agreed to be stronger
cryptanalysis and/or computer speeds may require a stronger hash mechanisms. Furthermore, future advances in cryptanalysis and/or
everywhere. In addition, the additional computation required by SHA1 computer speeds may require a stronger hash everywhere. In addition,
above that required by MD5 is insignificant compared with the the additional computation required by SHA1 above that required by
computational effort required by the RSA modular exponentiation. 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 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 and, so as to completely replace [RFC 2537], describes how to produce
RSA KEY RRs in Section 2. RSA KEY RRs in Section 2.
Implementation of the RSA algorithm in DNS with SHA1 is MANDATORY for 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] DNSSEC. The generation of RSA/MD5 SIG RRs as described in [RFC 2537]
is NOT RECOMMENDED. is NOT RECOMMENDED.
The key words "MUST", "REQUIRED", "SHOULD", "RECOMMENDED", "NOT The key words "MUST", "REQUIRED", "SHOULD", "RECOMMENDED", "NOT
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hex 30 21 30 09 06 05 2B 0E 03 02 1A 05 00 04 14 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 This prefix is included to make it easier to use standard
cryptographic libraries. The FF octet MUST be repeated the maximum cryptographic libraries. The FF octet MUST be repeated the maximum
INTERNET-DRAFT RSA/SHA1 in the DNS INTERNET-DRAFT RSA/SHA1 in the DNS
number of times such that the value of the quantity being number of times such that the value of the quantity being
exponentiated is one octet shorter than the value of n. exponentiated is one octet shorter than the value of n.
(The above specifications are identical to the corresponding part of (The above specifications are identical to the corresponding parts of
Public Key Cryptographic Standard #1 [RFC 2437].) Public Key Cryptographic Standard #1 [RFC 2437].)
The size of "n", including most and least significant bits (which 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 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 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 small. These are protocol limits. For a discussion of key size see
[RFC 2541]. [RFC 2541].
Leading zero bytes are permitted in the RSA/SHA1 algorithm signature. 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 4. Performance Considerations
General signature generation speeds are roughly the same for RSA and General signature generation speeds are roughly the same for RSA and
DSA [RFC 2536]. With sufficient pre-computation, signature DSA [RFC 2536]. With sufficient pre-computation, signature
generation with DSA is faster than RSA. Key generation is also generation with DSA is faster than RSA. Key generation is also
faster for DSA. However, signature verification is an order of faster for DSA. However, signature verification is an order of
magnitude slower with DSA when the RSA public exponent is chosen to 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 be small as is recommended for KEY RRs used in domain name system
(DNS) data authentication. (DNS) data authentication.
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. If a key is known to be used only for
authentication, as is the case with DNSSEC, then an exponent of 3 is
acceptable. However other applications in the future may wish to
leverage DNS distributed keys for applications that do require
confidentiality. For keys which might have such other uses, a more
conservative choice would be 65537 (F4, the fourth fermat number).
Current DNS implementations are optimized for small transfers, Current DNS implementations are optimized for small transfers,
typically less than 512 bytes including DNS overhead. Larger typically less than 512 bytes including DNS overhead. Larger
transfers will perform correctly and extensions have been transfers will perform correctly and extensions have been
standardized [RFC 2671] to make larger transfers more efficient, it standardized [RFC 2671] to make larger transfers more efficient, it
is still advisable at this time to make reasonable efforts to is still advisable at this time to make reasonable efforts to
minimize the size of KEY RR sets stored within the DNS consistent 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 with adequate security. Keep in mind that in a secure zone, at least
one authenticating SIG RR will also be returned. one authenticating SIG RR will also be returned.
5. IANA Considerations INTERNET-DRAFT RSA/SHA1 in the DNS
The DNSSEC algorithm number (TBD, 5 suggested) is allocated for 5. IANA Considerations
RSA/SHA1 SIG RRs and RSA KEY RRs.
INTERNET-DRAFT RSA/SHA1 in the DNS The DNSSEC algorithm number 5 is allocated for RSA/SHA1 SIG RRs and
RSA KEY RRs.
6. Security Considerations 6. Security Considerations
Many of the general security consideration in [RFC 2535] apply. Keys Many of the general security consideration in [RFC 2535] apply. Keys
retrieved from the DNS should not be trusted unless (1) they have retrieved from the DNS should not be trusted unless (1) they have
been securely obtained from a secure resolver or independently been securely obtained from a secure resolver or independently
verified by the user and (2) this secure resolver and secure verified by the user and (2) this secure resolver and secure
obtainment or independent verification conform to security policies obtainment or independent verification conform to security policies
acceptable to the user. As with all cryptographic algorithms, acceptable to the user. As with all cryptographic algorithms,
evaluating the necessary strength of the key is essential and evaluating the necessary strength of the key is essential and
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155 Beaver Street 155 Beaver Street
Milford, MA 01757 USA Milford, MA 01757 USA
Telephone: +1-508-261-5434 (w) Telephone: +1-508-261-5434 (w)
+1-508-634-2066 (h) +1-508-634-2066 (h)
FAX: +1-508-261-4777 (w) FAX: +1-508-261-4777 (w)
EMail: Donald.Eastlake@motorola.com EMail: Donald.Eastlake@motorola.com
Expiration and File Name Expiration and File Name
This draft expires in June 2001. This draft expires in October 2001.
Its file name is draft-ietf-dnsext-rsa-02.txt. Its file name is draft-ietf-dnsext-rsa-03.txt.
 End of changes. 

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