Internet DRAFT - draft-ietf-pkix-rfc5280-clarifications
draft-ietf-pkix-rfc5280-clarifications
INTERNET-DRAFT P. Yee
Intended Status: Proposed Standard AKAYLA
Updates: 5280 (if approved) October 31, 2012
Expires: May 4, 2013
Updates to the Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation List (CRL) Profile
<draft-ietf-pkix-rfc5280-clarifications-11.txt>
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Abstract
This document updates RFC 5280, the Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List (CRL)
Profile. This document changes the set of acceptable encoding
methods for the explicitText field of the user notice policy
qualifier and clarifies the rules for converting internationalized
domain name labels to ASCII. This document also provides some
clarifications on the use of self-signed certificates, trust anchors,
and some updated security considerations.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Update to RFC 5280, Section 3.2: Certification Paths and
Trust . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Update to RFC 5280, Section 4.2.1.4: Certificate Policies . . 3
4. Update to RFC 5280, Section 6.2: Using the Path Validation
Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Update to RFC 5280, Section 7.3: Internationalized Domain
Names in Distinguished Names . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . . 7
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
This document updates the Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation List (CRL) Profile [RFC5280].
This document makes a recommendation that self-signed certificates
used to convey trust anchor data be marked as CA certificates, which
is not always current practice.
The use of self-signed certificates as trust anchors in Section 6.2
is clarified. While it is optional to use additional information in
these certificates in the path validation process, [RFC5937] is noted
as providing guidance in that regard.
The acceptable and unacceptable encodings for the explicitText field
of the user notice policy qualifier are updated to bring them in line
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with existing practice.
The Section 7.3 rules for ASCII encoding of Internationalized Domain
Names (IDN) as Distinguished Names are aligned with the rules in
Section 7.2 which govern IDN encoding as GeneralNames.
In light of some observed attacks [Prins], the Security
Considerations now give added depth to the consequences of CA key
compromise. This section additionally notes that collision
resistance is not a required property of one-way hash functions when
used to generate key identifiers.
1.1. Terminology
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 RFC 2119 [RFC2119].
2. Update to RFC 5280, Section 3.2: Certification Paths and Trust
Add the following paragraph to the end of RFC 5280, Section 3.2:
| Consistent with Section 3.4.61 of X.509 (11/2008) [X.509] we note
| that use of self-issued certificates and self-signed certificates
| issued by other than CAs are outside the scope of this specification.
| Thus, for example, a web server or client might generate a self-
| signed certificate to identify itself. These certificates, and how a
| relying party uses them to authenticate asserted identities, are
| both outside the scope of RFC 5280.
3. Update to RFC 5280, Section 4.2.1.4: Certificate Policies
RFC 5280, Section 4.2.1.4, the tenth paragraph says:
| An explicitText field includes the textual statement directly in
| the certificate. The explicitText field is a string with a
| maximum size of 200 characters. Conforming CAs SHOULD use the
| UTF8String encoding for explicitText, but MAY use IA5String.
| Conforming CAs MUST NOT encode explicitText as VisibleString or
| BMPString. The explicitText string SHOULD NOT include any control
| characters (e.g., U+0000 to U+001F and U+007F to U+009F). When
| the UTF8String encoding is used, all character sequences SHOULD be
| normalized according to Unicode normalization form C (NFC) [NFC].
This paragraph is replaced with:
| An explicitText field includes the textual statement directly in
| the certificate. The explicitText field is a string with a
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| maximum size of 200 characters. Conforming CAs SHOULD use the
| UTF8String encoding for explicitText. VisibleString or BMPString
| are acceptable but less preferred alternatives. Conforming CAs
| MUST NOT encode explicitText as IA5String. The explicitText
| string SHOULD NOT include any control characters (e.g., U+0000 to
| U+001F and U+007F to U+009F). When the UTF8String or BMPString
| encoding is used, all character sequences SHOULD be normalized
| according to Unicode normalization form C (NFC) [NFC].
4. Update to RFC 5280, Section 6.2: Using the Path Validation Algorithm
RFC 5280, Section 6.2, the third paragraph says:
| Where a CA distributes self-signed certificates to specify trust
| anchor information, certificate extensions can be used to specify
| recommended inputs to path validation. For example, a policy
| constraints extension could be included in the self-signed
| certificate to indicate that paths beginning with this trust anchor
| should be trusted only for the specified policies. Similarly, a name
| constraints extension could be included to indicate that paths
| beginning with this trust anchor should be trusted only for the
| specified name spaces. The path validation algorithm presented in
| Section 6.1 does not assume that trust anchor information is provided
| in self-signed certificates and does not specify processing rules for
| additional information included in such certificates.
| Implementations that use self-signed certificates to specify trust
| anchor information are free to process or ignore such information.
This paragraph is replaced with:
| Where a CA distributes self-signed certificates to specify trust
| anchor information, certificate extensions can be used to specify
| recommended inputs to path validation. For example, a policy
| constraints extension could be included in the self-signed
| certificate to indicate that paths beginning with this trust anchor
| should be trusted only for the specified policies. Similarly, a name
| constraints extension could be included to indicate that paths
| beginning with this trust anchor should be trusted only for the
| specified name spaces. The path validation algorithm presented
| in Section 6.1 does not assume that trust anchor information is
| provided in self-signed certificates and does not specify processing
| rules for additional information included in such certificates.
| However, [RFC5914] defines several formats for representing trust
| anchor information, including self-signed certificates, and [RFC5937]
| provides an example of how such information may be used to initialize
| the path validation inputs. Implementations are free to make use of
| any additional information that is included in a trust anchor
| representation, or to ignore such information.
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5. Update to RFC 5280, Section 7.3: Internationalized Domain Names in
Distinguished Names
RFC 5280, Section 7.3, the first paragraph says:
| Domain Names may also be represented as distinguished names using
| domain components in the subject field, the issuer field, the
| subjectAltName extension, or the issuerAltName extension. As with
| the dNSName in the GeneralName type, the value of this attribute is
| defined as an IA5String. Each domainComponent attribute represents a
| single label. To represent a label from an IDN in the distinguished
| name, the implementation MUST perform the "ToASCII" label conversion
| specified in Section 4.1 of RFC 3490. The label SHALL be considered
| a "stored string". That is, the AllowUnassigned flag SHALL NOT be
| set.
This paragraph is replaced with:
| Domain Names may also be represented as distinguished names using
| domain components in the subject field, the issuer field, the
| subjectAltName extension, or the issuerAltName extension. As with
| the dNSName in the GeneralName type, the value of this attribute is
| defined as an IA5String. Each domainComponent attribute represents a
| single label. To represent a label from an IDN in the distinguished
| name, the implementation MUST perform the "ToASCII" label conversion
| specified in Section 4.1 of RFC 3490 with the UseSTD3ASCIIRules flag
| set. The label SHALL be considered a "stored string". That is, the
| AllowUnassigned flag SHALL NOT be set. The conversion process is the
| same as is performed in step 4 in Section 7.2.
6. Security Considerations
This document modifies the Security Considerations section of RFC
5280 as follows. The fifth paragraph of the Security Considerations
section of RFC 5280 says:
| The protection afforded private keys is a critical security factor.
| On a small scale, failure of users to protect their private keys will
| permit an attacker to masquerade as them or decrypt their personal
| information. On a larger scale, compromise of a CA's private signing
| key may have a catastrophic effect. If an attacker obtains the
| private key unnoticed, the attacker may issue bogus certificates and
| CRLs. Existence of bogus certificates and CRLs will undermine
| confidence in the system. If such a compromise is detected, all
| certificates issued to the compromised CA MUST be revoked, preventing
| services between its users and users of other CAs. Rebuilding after
| such a compromise will be problematic, so CAs are advised to
| implement a combination of strong technical measures (e.g., tamper-
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| resistant cryptographic modules) and appropriate management
| procedures (e.g., separation of duties) to avoid such an incident.
This paragraph is replaced with:
| The protection afforded private keys is a critical security factor.
| On a small scale, failure of users to protect their private keys will
| permit an attacker to masquerade as them or decrypt their personal
| information. On a larger scale, compromise of a CA's private signing
| key may have a catastrophic effect.
|
| If an attacker obtains the private key of a CA unnoticed, the
| attacker may issue bogus certificates and CRLs. Even if an attacker
| is unable to obtain a copy of a CA's private key, the attacker may be
| able to issue bogus certificates and CRLs by making unauthorized use
| of the CA's workstation or of an RA's workstation. Such an attack
| may be the result of an attacker obtaining unauthorized access to the
| workstation, either locally or remotely, or may be the result of
| inappropriate activity by an insider. Existence of bogus
| certificates and CRLs will undermine confidence in the system. Among
| many other possible attacks, the attacker may issue bogus
| certificates that have the same subject names as legitimate
| certificates in order impersonate legitimate certificate subjects.
| This could include bogus CA certificates in which the subject names
| in the bogus certificates match the names under which legitimate CAs
| issue certificates and CRLs. This would allow the attacker to issue
| bogus certificates and CRLs that have the same issuer names, and
| possibly the same serial numbers, as certificates and CRLs issued by
| legitimate CAs.
The following text is added to the end of the Security Considerations
section of 5280:
One-way hash functions are commonly used to generate key identifier
values (AKI and SKI), e.g., as described in Sections 4.1.1 and 4.1.2.
However, none of the security properties of such functions are required
for this context.
7. IANA Considerations
This document has no actions for IANA.
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8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation
List (CRL) Profile", RFC 5280, May 2008.
[RFC5914] Housley, R., Ashmore, S., and C. Wallace, "Trust Anchor
Format", RFC 5914, June 2010.
[X.509] ITU-T Recommendation X.509 (2008) | ISO/IEC 9594-8:2008,
Information Technology - Open systems interconnection -
The Directory: Public-key and attribute certificate
frameworks
8.2. Informative References
[RFC5937] Ashmore, S. and C. Wallace, "Using Trust Anchor
Constraints during Certification Path Processing",
RFC 5937, August 2010.
[Prins] Prins, J. R., "DigiNotar Certificate Authority breach
'Operation Black Tulip'", September, 2011,
<http://www.rijksoverheid.nl/bestanden/documenten-en-
publicaties/rapporten/2011/09/05/diginotar-public-report-
version-1/rapport-fox-it-operation-black-tulip-v1-0.pdf>
[X.680] ITU-T Recommendation X.680 (2002) | ISO/IEC 8824-1:2002,
Information Technology - Abstract Syntax Notation One
(ASN.1): Specification of basic notation.
[NFC] Davis, M. and M. Duerst, "Unicode Standard Annex #15:
Unicode Normalization Forms", October 2006,
<http://www.unicode.org/reports/tr15/>.
9. Acknowledgements
David Cooper is acknowledged for his fine work in editing previous
versions of this document.
Author's Address
Peter E. Yee
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AKAYLA
7150 Moorland Drive
Clarksville, MD 21029
USA
EMail: peter@akayla.com
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