draft-ietf-hip-cert-05.txt   draft-ietf-hip-cert-06.txt 
Host Identity Protocol Heer Host Identity Protocol Heer
Internet-Draft Distributed Systems Group, RWTH Internet-Draft Distributed Systems Group, RWTH
Intended status: Experimental Aachen University Intended status: Experimental Aachen University
Expires: May 12, 2011 Varjonen Expires: May 23, 2011 Varjonen
Helsinki Institute for Information Helsinki Institute for Information
Technology Technology
November 8, 2010 November 19, 2010
Host Identity Protocol Certificates Host Identity Protocol Certificates
draft-ietf-hip-cert-05 draft-ietf-hip-cert-06
Abstract Abstract
The CERT parameter is a container for X.509.v3 certificates and The CERT parameter is a container for X.509.v3 certificates and
Simple Public Key Infrastructure (SPKI) certificates. It is used for Simple Public Key Infrastructure (SPKI) certificates. It is used for
carrying these certificates in Host Identity Protocol (HIP) control carrying these certificates in Host Identity Protocol (HIP) control
packets. This document only specifies the certificate parameter and packets. This document specifies the certificate parameter and the
the error signaling in case of a failed verification. The use of error signaling in case of a failed verification. Additionally, this
certificates including how certificates are obtained, requested, and document specifies the representations of Host Identity Tags in
which actions are taken upon successful or failed verification are to X.509.v3 and SPKI certificates.
be defined in the documents that use the certificate parameter.
Additionally, this document specifies the representations of Host The concrete use of certificates including how certificates are
Identity Tags in X.509.v3 and SPKI certificates. obtained, requested, and which actions are taken upon successful or
failed verification are specific to the scenario in which the
certificates are used. Hence, the definition of these scenario-
specific aspects are left to the documents that use the CERT
parameter.
Status of this Memo Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79. This document may not be modified, provisions of BCP 78 and BCP 79. This document may not be modified,
and derivative works of it may not be created, except to format it and derivative works of it may not be created, except to format it
for publication as an RFC or to translate it into languages other for publication as an RFC or to translate it into languages other
than English. than English.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on May 12, 2011. This Internet-Draft will expire on May 23, 2011.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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described in the BSD License. described in the BSD License.
1. Introduction 1. Introduction
Digital certificates bind a piece of information to a public key by Digital certificates bind a piece of information to a public key by
means of a digital signature, and thus, enable the holder of a means of a digital signature, and thus, enable the holder of a
private key to generate cryptographically verifiable statements. The private key to generate cryptographically verifiable statements. The
Host Identity Protocol (HIP) [RFC5201] defines a new cryptographic Host Identity Protocol (HIP) [RFC5201] defines a new cryptographic
namespace based on asymmetric cryptography. The identity of each namespace based on asymmetric cryptography. The identity of each
host is derived from a public key, allowing hosts to digitally sign host is derived from a public key, allowing hosts to digitally sign
data with their private key. This document specifies the CERT data and issue certificates with their private key. This document
parameter, which is used to transmit digital certificates in HIP. It specifies the CERT parameter, which is used to transmit digital
fills the placeholder specified in Section 5.2 of [RFC5201]. certificates in HIP. It fills the placeholder specified in Section
5.2 of [RFC5201].
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
2. CERT Parameter 2. CERT Parameter
The CERT parameter is a container for certain types of digital The CERT parameter is a container for certain types of digital
skipping to change at page 2, line 45 skipping to change at page 3, line 4
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
2. CERT Parameter 2. CERT Parameter
The CERT parameter is a container for certain types of digital The CERT parameter is a container for certain types of digital
certificates. It MAY either carry SPKI certificates or X.509.v3 certificates. It MAY either carry SPKI certificates or X.509.v3
certificates. It does not specify any certificate semantics. certificates. It does not specify any certificate semantics.
However, it defines supplementary parameters that help HIP hosts to However, it defines supplementary parameters that help HIP hosts to
transmit semantically grouped CERT parameters in a more systematic transmit semantically grouped CERT parameters in a more systematic
way. The specific use of the CERT parameter for different use cases way. The specific use of the CERT parameter for different use cases
is intentionally not discussed in this document. is intentionally not discussed in this document because it is
specific to a concrete use case. Hence, the use of the CERT
parameter will be defined in the documents that use the CERT
parameter.
The CERT parameter is covered, when present, by the HIP SIGNATURE The CERT parameter is covered, when present, by the HIP SIGNATURE
field and is a non-critical parameter. field and is a non-critical parameter.
The CERT parameter can be used in all HIP packets but using it in the The CERT parameter can be used in all HIP packets. However, using it
I1 packet is not recommended because it can increase the processing in the I1 packet is not recommended because it can increase the
times of I1s, which can be problematic when processing storms of I1s. processing times of I1s, which can be problematic when processing
Each HIP control packet MAY contain multiple CERT parameters. These storms of I1s. Each HIP control packet MAY contain multiple CERT
parameters MAY be related or unrelated. Related certificates are parameters. These parameters MAY be related or unrelated. Related
managed in Cert groups. A Cert group specifies a group of related certificates are managed in Cert groups. A Cert group specifies a
CERT parameters that SHOULD be interpreted in a certain order (e.g. group of related CERT parameters that SHOULD be interpreted in a
for expressing certificate chains). For grouping CERT parameters, certain order (e.g., for expressing certificate chains). For
the Cert group and the Cert count field MUST be set. Ungrouped grouping CERT parameters, the Cert group and the Cert count field
certificates exhibit a unique Cert group field and set the Cert count MUST be set. Ungrouped certificates exhibit a unique Cert group
to 1. CERT parameters with the same Cert group number in the group field and set the Cert count to 1. CERT parameters with the same
field indicate a logical grouping. The Cert count field indicates Cert group number in the group field indicate a logical grouping.
the number of CERT parameters in the group. The Cert count field indicates the number of CERT parameters in the
group.
CERT parameters that belong to the same Cert group MAY be contained CERT parameters that belong to the same Cert group MAY be contained
in multiple sequential HIP control packets. This is indicated by a in multiple sequential HIP control packets. This is indicated by a
higher Cert count than the amount of CERT parameters with matching higher Cert count than the amount of CERT parameters with matching
Cert group fields in a HIP control packet. The CERT parameters MUST Cert group fields in a HIP control packet. The CERT parameters MUST
be placed in ascending order, within a HIP control packet, according be placed in ascending order, within a HIP control packet, according
to their Cert group field. Cert groups MAY only span multiple to their Cert group field. Cert groups MAY only span multiple
packets if the Cert group does not fit the packet. Only a single packets if the Cert group does not fit the packet. A HIP packet MUST
Cert group MAY span two subsequent packets. NOT contain more than one incomplete Cert group that continues in the
next HIP control packet.
The Cert ID acts as a sequence number to identify the certificates in The Cert ID acts as a sequence number to identify the certificates in
a Cert group. The numbers in the Cert ID field MUST start from 1 up a Cert group. The numbers in the Cert ID field MUST start from 1 up
to Cert count. to Cert count.
The Cert Group and Cert ID namespaces are managed locally by each The Cert Group and Cert ID namespaces are managed locally by each
host that sends CERT parameters in HIP control packets. host that sends CERT parameters in HIP control packets.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
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[RFC1779]. Using the DN encoding results in smaller HIP control [RFC1779]. Using the DN encoding results in smaller HIP control
packets, but requires the receiver to retrieve the certificate or packets, but requires the receiver to retrieve the certificate or
check a local cache against the DN. check a local cache against the DN.
3. X.509.v3 Certificate Object and Host Identities 3. X.509.v3 Certificate Object and Host Identities
When using X.509.v3 certificates to transmit information related to When using X.509.v3 certificates to transmit information related to
HIP hosts, HITs MAY be enclosed within the certificates. HITs can HIP hosts, HITs MAY be enclosed within the certificates. HITs can
represent an issuer, a subject, or both. In X.509.v3 HITs are represent an issuer, a subject, or both. In X.509.v3 HITs are
represented as issuer or subject alternative name extensions as represented as issuer or subject alternative name extensions as
defined in [RFC2459]. If only HIT of the host is presented as either defined in [RFC2459]. If only the HIT of the host is presented as
the issuer or the subject the respective HIT MUST be placed into the either the issuer or the subject the respective HIT MUST be placed
respective entity's DN's Common Name (CN) section in a colon into the respective entity's DN's Common Name (CN) section in a colon
delimited presentation format defined in [RFC5952]. Inclusion of CN delimited presentation format defined in [RFC5952]. Inclusion of CN
is not necessary if DN contains any other naming information. It is is not necessary if DN contains any other naming information. It is
RECOMMENDED to use the FQDN/NAI from the hosts HOST_ID parameter in RECOMMENDED to use the FQDN/NAI from the hosts HOST_ID parameter in
the DN if one exists. The full HIs are presented in the public key the DN if one exists. The full HIs are presented in the public key
entries of X.509.v3 certificates. entries of X.509.v3 certificates.
The following examples illustrate how HITs are presented as issuer The following examples illustrate how HITs are presented as issuer
and subject in the DN and in the X.509.v3 extension alternative and subject in the DN and in the X.509.v3 extension alternative
names. names.
Format of DN: Format of DN:
Issuer: CN=hit-of-issuer Issuer: CN=hit-of-issuer
Subject: CN=hit-of-issuer Subject: CN=hit-of-issuer
Example DN: Example DN:
Issuer: CN=2001:14:6cf:fae7:bb79:bf78:7d64:c056 Issuer: CN=2001:14:6cf:fae7:bb79:bf78:7d64:c056
Subject: CN=2001:1c:5a14:26de:a07c:385b:de35:60e3 Subject: CN=2001:1c:5a14:26de:a07c:385b:de35:60e3
Format of X509v3 extensions: Format of X509v3 extensions:
X509v3 Issuer Alternative Name: X509v3 Issuer Alternative Name:
IP Address:HIT-OF-ISSUER IP Address:hit-of-issuer
X509v3 Subject Alternative Name: X509v3 Subject Alternative Name:
IP Address:HIT-OF-SUBJECT IP Address:hit-of-subject
Example X509v3 extensions: Example X509v3 extensions:
X509v3 Issuer Alternative Name: X509v3 Issuer Alternative Name:
IP Address:2001:14:6CF:FAE7:BB79:BF78:7D64:C056 IP Address:2001:14:6cf:fae7:bb79:bf78:7d64:c056
X509v3 Subject Alternative Name: X509v3 Subject Alternative Name:
IP Address:2001:1C:5A14:26DE:A07C:385B:DE35:60E3 IP Address:2001:1C:5a14:26de:a07C:385b:de35:60e3
Appendix B shows a full example X.509.v3 certificate with HIP Appendix B shows a full example X.509.v3 certificate with HIP
content. content.
As another example, consider a managed PKI environment in which the As another example, consider a managed PKI environment in which the
peers have certificates that are anchored in (potentially different) peers have certificates that are anchored in (potentially different)
managed trust chains. In this scenario, the certificates issued to managed trust chains. In this scenario, the certificates issued to
HIP hosts are signed by intermediate Certificate Authorities (CAs) up HIP hosts are signed by intermediate Certificate Authorities (CAs) up
to a root CA. In this example, the managed PKI environment is to a root CA. In this example, the managed PKI environment is
neither HIP aware, nor can it be configured to compute HITs and neither HIP aware, nor can it be configured to compute HITs and
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the HIP peers have and use some mechanism of checking peer the HIP peers have and use some mechanism of checking peer
certificate validity for revocation, signature, minimum cryptographic certificate validity for revocation, signature, minimum cryptographic
strength, etc., up to the trusted root CA. strength, etc., up to the trusted root CA.
When HIP communications are established, the HIP hosts not only need When HIP communications are established, the HIP hosts not only need
to send their identity certificates (or pointers to their to send their identity certificates (or pointers to their
certificates), but also the chain of intermediate CAs (or pointers to certificates), but also the chain of intermediate CAs (or pointers to
the CAs) up to the root CA, or to a CA that is trusted by the remote the CAs) up to the root CA, or to a CA that is trusted by the remote
peer. This chain of certificates MUST be sent in a Cert group as peer. This chain of certificates MUST be sent in a Cert group as
specified in Section 2. The HIP peers validate each other's specified in Section 2. The HIP peers validate each other's
Certificates and compute peer HITs based on the Certificate public certificates and compute peer HITs based on the certificate public
keys. keys.
4. SPKI Cert Object and Host Identities 4. SPKI Cert Object and Host Identities
When using SPKI certificates to transmit information related to HIP When using SPKI certificates to transmit information related to HIP
hosts, HITs need to be enclosed within the certificates. HITs can hosts, HITs need to be enclosed within the certificates. HITs can
represent an issuer, a subject, or both. In the following we define represent an issuer, a subject, or both. In the following we define
the representation of those identifiers for SPKI given as the representation of those identifiers for SPKI given as
S-expressions. Note that the S-expressions are only the human- S-expressions. Note that the S-expressions are only the human-
readable representation of SPKI certificates. Full HIs are presented readable representation of SPKI certificates. Full HIs are presented
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follows: follows:
Format: (hash hit hit-of-host) Format: (hash hit hit-of-host)
Example: (hash hit 2001:13:724d:f3c0:6ff0:33c2:15d8:5f50) Example: (hash hit 2001:13:724d:f3c0:6ff0:33c2:15d8:5f50)
Appendix A shows a full example SPKI certificate with HIP content. Appendix A shows a full example SPKI certificate with HIP content.
5. Revocation of Certificates 5. Revocation of Certificates
Revocation of X.509.v3 certificates is handled as defined in Section Revocation of X.509.v3 certificates is handled as defined in Section
5 in [RFC2459]. Revocation of SPKI certificates is handled as 5 of [RFC2459]. Revocation of SPKI certificates is handled as
defined in Section 5 in [RFC2693]. defined in Section 5 of [RFC2693].
6. Error signaling 6. Error signaling
If the Initiator does not send the certificate that the Responder If the Initiator does not send the certificate that the Responder
requires the Responder may take actions (e.g. reject the connection). requires the Responder may take actions (e.g. reject the connection).
The Responder MAY signal this to the Initiator by sending a HIP The Responder MAY signal this to the Initiator by sending a HIP
NOTIFY message with NOTIFICATION parameter error type NOTIFY message with NOTIFICATION parameter error type
CREDENTIALS_NEEDED. CREDENTIALS_NEEDED.
If the verification of a certificate fails, a verifier MAY signal If the verification of a certificate fails, a verifier MAY signal
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In Section 6 this document defines two new types for "NOTIFY message In Section 6 this document defines two new types for "NOTIFY message
types" sub-registry under "Host Identity Protocol (HIP) Parameters". types" sub-registry under "Host Identity Protocol (HIP) Parameters".
8. Security Considerations 8. Security Considerations
Certificate grouping allows the certificates to be sent in multiple Certificate grouping allows the certificates to be sent in multiple
consecutive packets. This might allow similar attacks as IP-layer consecutive packets. This might allow similar attacks as IP-layer
fragmentation allows, for example sending of fragments in wrong order fragmentation allows, for example sending of fragments in wrong order
and skipping some fragments to delay or stall packet processing by and skipping some fragments to delay or stall packet processing by
the victim in order to use resources (e.g. CPU or memory). the victim in order to use resources (e.g. CPU or memory). Hence,
hosts SHOULD implement mechanisms to discard certificate groups with
outstanding certificates if state space is scarce.
It is NOT RECOMMENDED to use grouping or hash and URL encodings when It is NOT RECOMMENDED to use grouping or hash and URL encodings when
HIP aware middleboxes are anticipated to be present on the HIP aware middleboxes are anticipated to be present on the
communication path between peers because fetching remote certificates communication path between peers because fetching remote certificates
require the middlebox to buffer the packets and to request remote require the middlebox to buffer the packets and to request remote
data. This makes these devices prone to denial of service (DoS) data. This makes these devices prone to denial of service (DoS)
attacks. Moreover, middleboxes and responders that request remote attacks. Moreover, middleboxes and responders that request remote
certificates can be used as deflectors for distributed denial of certificates could be used as deflectors for distributed denial of
service attacks. service attacks.
9. Acknowledgements 9. Acknowledgements
The authors would like to thank A. Keranen, D. Mattes, M. Komu and T. The authors would like to thank A. Keranen, D. Mattes, M. Komu and T.
Henderson for the fruitful conversations on the subject. D. Mattes Henderson for the fruitful conversations on the subject. D. Mattes
most notably contributed the non-HIP aware use case in Section 3. most notably contributed the non-HIP aware use case in Section 3.
10. References 10. References
skipping to change at page 11, line 31 skipping to change at page 11, line 35
cc:a2:57:ac:b6:e2:6a:bc:1e:bd:cf:75:30:95:5b: cc:a2:57:ac:b6:e2:6a:bc:1e:bd:cf:75:30:95:5b:
92:af:75:55:69:0b:c3:48:0f:b5:e4:15:30:79:89: 92:af:75:55:69:0b:c3:48:0f:b5:e4:15:30:79:89:
22:b3:fd:7e:51:59:d2:0d:d7:12:5d:44:f3:e8:05: 22:b3:fd:7e:51:59:d2:0d:d7:12:5d:44:f3:e8:05:
13:1f:5b:4f:89:fa:1e:6d:83:e9:e2:cf:bd:5c:6f: 13:1f:5b:4f:89:fa:1e:6d:83:e9:e2:cf:bd:5c:6f:
ef:02:1e:c8:db:9a:48:9a:35:b8:b8:be:89:be:ab: ef:02:1e:c8:db:9a:48:9a:35:b8:b8:be:89:be:ab:
c8:dd:60:44:df:ac:01:b7:76:66:ab:5d:a1:a5:d0: c8:dd:60:44:df:ac:01:b7:76:66:ab:5d:a1:a5:d0:
3c:8d:22:04:d4:24:59:60:0f 3c:8d:22:04:d4:24:59:60:0f
Exponent: 65537 (0x10001) Exponent: 65537 (0x10001)
X509v3 extensions: X509v3 extensions:
X509v3 Issuer Alternative Name: X509v3 Issuer Alternative Name:
IP Address:2001:1E:D709:1980:5C6A:BB0C:7650:A027 IP Address:2001:1e:d709:1980:5c6a:bb0C:7650:a027
X509v3 Subject Alternative Name: X509v3 Subject Alternative Name:
IP Address:2001:1C:5A14:26DE:A07C:385B:DE35:60E3 IP Address:2001:1c:5a14:26de:a07c:385b:de35:60e3
Signature Algorithm: sha1WithRSAEncryption Signature Algorithm: sha1WithRSAEncryption
48:a1:25:fb:01:31:d9:80:76:1b:1a:2d:00:f1:26:22:3c:3b: 48:a1:25:fb:01:31:d9:80:76:1b:1a:2d:00:f1:26:22:3c:3b:
20:a0:cb:b2:28:d2:0c:21:d3:9e:3b:4a:ab:3d:f6:ea:ad:46: 20:a0:cb:b2:28:d2:0c:21:d3:9e:3b:4a:ab:3d:f6:ea:ad:46:
f6:f5:c4:4f:71:ce:3e:7b:65:8d:58:75:2e:99:25:82:5f:73: f6:f5:c4:4f:71:ce:3e:7b:65:8d:58:75:2e:99:25:82:5f:73:
10:c6:c2:f0:4b:35:ff:5c:65:ac:fc:a4:a7:76:50:ab:62:50: 10:c6:c2:f0:4b:35:ff:5c:65:ac:fc:a4:a7:76:50:ab:62:50:
b8:86:21:e6:83:e1:c1:3d:20:c9:8e:13:ab:d7:4b:d4:ab:2d: b8:86:21:e6:83:e1:c1:3d:20:c9:8e:13:ab:d7:4b:d4:ab:2d:
72:9d:f0:9f:5f:e0:6f:95:fa:a1:95:64:3f:74:63:e5:a8:1d: 72:9d:f0:9f:5f:e0:6f:95:fa:a1:95:64:3f:74:63:e5:a8:1d:
f7:e6:48:98:33:53:7b:91:6d:b0:cb:af:32:15:8c:e0:01:a0: f7:e6:48:98:33:53:7b:91:6d:b0:cb:af:32:15:8c:e0:01:a0:
a0:b8 a0:b8
Appendix C. Change log Appendix C. Change log
Changes from version 00 to 01: Changes from version 00 to 01:
o Revised text about DN usage. o Revised text on DN usage.
o Revised text about Cert group usage. o Revised text on Cert group usage.
Changes from version 01 to 02: Changes from version 01 to 02:
o Revised the type numbers. o Revised the type numbers.
o Added a section about signaling. o Added a section on signaling.
Changes from version 02 to 03: Changes from version 02 to 03:
o Revised text about CERT use in control packets. o Revised text on CERT usage in control packets.
Changes from version 03 to 04: Changes from version 03 to 04:
o Added the non-HIP aware use case to the Section 3. o Added the non-HIP aware use case to the Section 3.
o Clarified that the HITs are not always required in the o Clarified that the HITs are not always required in the
certificates. certificates.
o Rewrote the signaling section. o Rewrote the signaling section.
skipping to change at page 13, line 7 skipping to change at page 13, line 16
o Clarifications to Section Section 3. o Clarifications to Section Section 3.
o Modified the explanation of INVALID_CERTIFICATE to allow multiple o Modified the explanation of INVALID_CERTIFICATE to allow multiple
certs. certs.
o Added reference to the IPv6 colon delimited presentation format. o Added reference to the IPv6 colon delimited presentation format.
o Small editorial changes. o Small editorial changes.
Changes from version 05 to 06:
o Editorial changes.
o Unified the example in Section 3.
Authors' Addresses Authors' Addresses
Tobias Heer Tobias Heer
Distributed Systems Group, RWTH Aachen University Distributed Systems Group, RWTH Aachen University
Ahornstrasse 55 Ahornstrasse 55
Aachen Aachen
Germany Germany
Phone: +49 241 80 214 36 Phone: +49 241 80 214 36
Email: heer@cs.rwth-aachen.de Email: heer@cs.rwth-aachen.de
 End of changes. 26 change blocks. 
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