Movatterモバイル変換

Internet Engineering Task Force (IETF)                            P. YeeRequest for Comments: 6818                                        AKAYLAUpdates:5280                                               January 2013Category: Standards TrackISSN: 2070-1721Updates to the Internet X.509 Public Key InfrastructureCertificate and Certificate Revocation List (CRL) ProfileAbstract   This document updatesRFC 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.Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6818.Yee                          Standards Track                    [Page 1]

RFC 6818RFC 5280 Clarifications            January 2013Copyright Notice   Copyright (c) 2013 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Table of Contents1. Introduction ....................................................21.1. Terminology ................................................3   2. Update toRFC 5280, Section 3.2: "Certification Paths and Trust" 33. Update toRFC 5280, Section 4.2.1.4: "Certificate Policies" .....3   4. Update toRFC 5280, Section 6.2: "Using the Path Validation      Algorithm" ......................................................4   5. Update toRFC 5280, Section 7.3: "Internationalized      Domain Names in Distinguished Names" ............................56. Security Considerations .........................................57. Update toRFC 5280, Section 11.1: "Normative References" ........78. Update toRFC 5280, Section 11.2: "Informative References" ......79. References ......................................................79.1. Normative References .......................................79.2. Informative References .....................................710. Acknowledgements ................................................81.  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 certificate authority   (CA) certificates, which is not always current practice.   The use of self-signed certificates as trust anchors inSection 6.2   of [RFC5280] 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.Yee                          Standards Track                    [Page 2]

RFC 6818RFC 5280 Clarifications            January 2013   The acceptable and unacceptable encodings for the explicitText field   of the user notice policy qualifier are updated to bring them in line   with existing practice.   The rules inSection 7.3 of [RFC5280] for ASCII encoding of   Internationalized Domain Names (IDNs) as Distinguished Names are   aligned with the rules inSection 7.2 of that document that govern   IDN encoding as GeneralNames.   In light of some observed attacks [Prins], the Security   Considerations section now gives 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.   This document also adds normative and informative references for   Trust Anchor formats and how they may be used to initialize the path   validation inputs.  These are needed as a result of the changes made   inSection 4 of this document.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 inRFC 2119 [RFC2119].2.  Update toRFC 5280, Section 3.2: "Certification Paths and Trust"   Add the following paragraph to the end ofRFC 5280, Section 3.2:| Consistent withSection 3.4.61 of X.509 (11/2008) [X.509], we note| that use of self-issued certificates and self-signed certificates| issued by entities 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 ofRFC 5280.3.  Update toRFC 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 controlYee                          Standards Track                    [Page 3]

RFC 6818RFC 5280 Clarifications            January 2013| 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  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 toRFC 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 inSection 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 inYee                          Standards Track                    [Page 4]

RFC 6818RFC 5280 Clarifications            January 2013Section 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.5.  Update toRFC 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 inSection 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 inSection 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 inSection 7.2.6.  Security Considerations   This document modifies the Security Considerations section ofRFC5280 as follows.  The fifth paragraph of the Security Considerations   section ofRFC 5280 says:Yee                          Standards Track                    [Page 5]

RFC 6818RFC 5280 Clarifications            January 2013  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-| 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.Yee                          Standards Track                    [Page 6]

RFC 6818RFC 5280 Clarifications            January 2013   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 Sections4.1.1 and4.1.2.| However, none of the security properties of such functions are| required for this context.7.  Update toRFC 5280, Section 11.1: "Normative References"   [RFC5914]   Housley, R., Ashmore, S., and C. Wallace, "Trust Anchor               Format",RFC 5914, June 2010.8.  Update toRFC 5280, Section 11.2: "Informative References"   [RFC5937]   Ashmore, S. and C. Wallace, "Using Trust Anchor               Constraints during Certification Path Processing",RFC 5937, August 2010.9.  References9.1.  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.9.2.  Informative References   [RFC5937]   Ashmore, S. and C. Wallace, "Using Trust Anchor               Constraints during Certification Path Processing",RFC5937, August 2010.Yee                          Standards Track                    [Page 7]

RFC 6818RFC 5280 Clarifications            January 2013   [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>.   [NFC]       Davis, M. and M. Duerst, "Unicode Standard Annex #15:               Unicode Normalization Forms", October 2006,               <http://www.unicode.org/reports/tr15/>.10.  Acknowledgements   David Cooper is acknowledged for his fine work in editing previous   versions of this document.Author's Address   Peter E. Yee   AKAYLA   7150 Moorland Drive   Clarksville, MD 21029   USA   EMail: peter@akayla.comYee                          Standards Track                    [Page 8]