Network Working Group S. Raza
Internet-Draft J. Hoeglund
Intended status: Standards Track RISE AB
Expires: May 6, 2021 G. Selander
J. Mattsson
Ericsson AB
M. Furuhed
Nexus Group
November 02, 2020
CBOR Profile of X.509 Certificates
draft-mattsson-cose-cbor-cert-compress-02
Abstract
This document specifies a CBOR encoding/compression of RFC 7925
profiled certificates. By using the fact that the certificates are
profiled, the CBOR certificate compression algorithms can in many
cases compress RFC 7925 profiled certificates with over 50%. This
document also specifies COSE headers for CBOR encoded certificates as
well as the use of the CBOR certificate compression algorithm with
TLS Certificate Compression in TLS 1.3 and DTLS 1.3.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on May 6, 2021.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Notational Conventions . . . . . . . . . . . . . . . . . . . 4
3. CBOR Encoding . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Message Fields . . . . . . . . . . . . . . . . . . . . . 4
3.2. Encoding of Extensions . . . . . . . . . . . . . . . . . 7
4. Compliance Requirements for Constrained IoT . . . . . . . . . 8
5. Deployment settings . . . . . . . . . . . . . . . . . . . . . 8
6. Expected Certificate Sizes . . . . . . . . . . . . . . . . . 8
7. Natively Signed CBOR Certificates . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9.1. CBOR Certificate Types Registry . . . . . . . . . . . . . 10
9.2. CBOR Attribute Type Registry . . . . . . . . . . . . . . 10
9.3. CBOR Certificate Signature Algorithms Registry . . . . . 11
9.4. CBOR Certificate Public Key Algorithms Registry . . . . . 12
9.5. COSE Header Parameters Registry . . . . . . . . . . . . . 12
9.6. TLS Certificate Compression Algorithm IDs Registry . . . 12
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
10.1. Normative References . . . . . . . . . . . . . . . . . . 13
10.2. Informative References . . . . . . . . . . . . . . . . . 14
Appendix A. Example CBOR Certificates . . . . . . . . . . . . . 15
A.1. Example X.509 Certificate . . . . . . . . . . . . . . . . 15
A.2. Example CBOR Certificate Compression . . . . . . . . . . 16
A.3. Example: Natively Signed CBOR Certificate . . . . . . . . 16
Appendix B. X.509 Certificate Profile, ASN.1 . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction
One of the challenges with deploying a Public Key Infrastructure
(PKI) for the Internet of Things (IoT) is the size and encoding of
X.509 public key certificates [RFC5280], since those are not
optimized for constrained environments [RFC7228]. More compact
certificate representations are desirable. Due to the current PKI
usage of X.509 certificates, keeping X.509 compatibility is necessary
at least for a transition period. However, the use of a more compact
encoding with the Concise Binary Object Representation (CBOR)
[RFC7049] reduces the certificate size significantly which has known
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performance benefits in terms of decreased communication overhead,
power consumption, latency, storage, etc.
CBOR is a data format designed for small code size and small message
size. CBOR builds on the JSON data model but extends it by e.g.
encoding binary data directly without base64 conversion. In addition
to the binary CBOR encoding, CBOR also has a diagnostic notation that
is readable and editable by humans. The Concise Data Definition
Language (CDDL) [RFC8610] provides a way to express structures for
protocol messages and APIs that use CBOR. [RFC8610] also extends the
diagnostic notation.
CBOR data items are encoded to or decoded from byte strings using a
type-length-value encoding scheme, where the three highest order bits
of the initial byte contain information about the major type. CBOR
supports several different types of data items, in addition to
integers (int, uint), simple values (e.g. null), byte strings (bstr),
and text strings (tstr), CBOR also supports arrays [] of data items,
maps {} of pairs of data items, and sequences of data items. For a
complete specification and examples, see [RFC7049], [RFC8610], and
[RFC8742].
RFC 7925 [RFC7925] specifies a certificate profile for Internet of
Things deployments which can be applied for lightweight certificate
based authentication with e.g. TLS [RFC8446], DTLS
[I-D.ietf-tls-dtls13], COSE [RFC8152], or EDHOC
[I-D.ietf-lake-edhoc]. This document specifies the CBOR encoding/
compression of [RFC7925] profiled X.509 certificates based on
[X.509-IoT]. Two variants are defined using exactly the same CBOR
encoding and differing only in what is being signed:
o The CBOR compressed X.509 certificate, which can be decompressed
into a certificate that can be verified by code compatible with
[RFC7925].
o The "natively signed" CBOR encoded certificate, which further
optimizes the performance in constrained environments but is not
backwards compatible with [RFC7925], see Section 7.
Other work has looked at reducing the size of X.509 certificates.
The purpose of this document is to stimulate a discussion on CBOR
based certificates: what field values (in particular for
'issuer'/'subject') are relevant for constrained IoT applications,
what is the potential savings that can be expected with the proposed
encoding, and what is the right trade-off between compactness and
generality. The current version specifies a certificate encoding
which can support large parts of [RFC5280], and at the same time can
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maintain a small message size for certificates compatible with
[RFC7925].
This document specifies COSE headers for use of the CBOR certificate
encoding with COSE. The document also specifies the CBOR certificate
compression algorithm for use as TLS Certificate Compression with TLS
1.3 and DTLS 1.3.
2. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This specification makes use of the terminology in [RFC7228].
3. CBOR Encoding
This section specifies the content and encoding for CBOR
certificates, with the overall objective to produce a very compact
representation of the certificate profile defined in [RFC7925]. The
CBOR certificate can be either a CBOR compressed X.509 certificate,
in which case the signature is calculated on the DER encoded ASN.1
data in the X.509 certificate, or a natively signed CBOR certificate,
in which case the signature is calculated directly on the CBOR
encoded data (see Section 7). In both cases the certificate content
is adhering to the restrictions given by [RFC7925]. The
corresponding ASN.1 schema is given in Appendix A.
3.1. Message Fields
The encoding and compression has several components including: ASN.1
DER and base64 encoding are replaced with CBOR encoding, static
fields are elided, and elliptic curve points are compressed. The
X.509 fields and their CBOR encodings are listed below. Combining
these different components reduces the certificate size
significantly, which is not possible with general purpose
compressions algorithms, see Figure 1.
CBOR certificates are defined in terms of [RFC7925] profiled X.509
certificates:
o version. The 'version' field is known (fixed to v3), and is
omitted in the CBOR encoding.
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o serialNumber. The 'serialNumber' field is encoded as a CBOR byte
string. This allows encoding of all lengths with minimal
overhead.
o signatureAlgorithm. The 'signatureAlgorithm' field is encoded as
a CBOR int (see Section 9).
o signature. The 'signature' field is always the same as the
'signatureAlgorithm' field and always omitted from the CBOR
encoding.
o issuer. In the general case, the sequence of
'RelativeDistinguishedName' is encoded as CBOR array of CBOR maps,
where each AttributeTypeAndValue is encoded as a (CBOR int, CBOR
byte string) pair. Each AttributeType is encoded as a CBOR int
(see Figure 3), where the sign is used to represent the character
string type; positive for printableString, negative for
utf8String. If only a single 'RelativeDistinguishedName' is
present, the array is omitted and issuer is encoded as a CBOR map.
If a RelativeDistinguishedName contains a single
AttributeTypeAndValue containing an utf8String encoded 'common
name', the AttributeValue is encoded as a CBOR text string. If
the utf8String encoded 'common name' contains an EUI-64 mapped
from a 48-bit MAC address it is encoded as a CBOR byte string of
length 6. Other EUI-64 is encoded as a CBOR byte string of length
8.
o validity. The 'notBefore' and 'notAfter' UTCTime fields are ASCII
string of the form "yymmddHHMMSSZ". They are encoded as the
unsigned integers using the following invertible encoding
(Horner's method with different bases). The resulting integer n
always fit in a 32 bit usigned integer.
n = SS + 60 * (MM + 60 * (HH + 24 * (dd + 32 * (mm + 13 * yy))))
Decoding can be done by a succession of modulo and substraction
operations. I.e. SS = n mod 60, MM = ((n - SS) / 60) mod 60,
etc.
o subject. The 'subject' is encoded exactly like issuer.
o subjectPublicKeyInfo. The 'algorithm' field is encoded as a CBOR
int (see Section 9). The 'subjectPublicKey' field is encoded as a
CBOR byte string. Public keys of type id-ecPublicKey are point
compressed as defined in Section 2.3.3 of [SECG].
o extensions. The 'extensions' field is encoded as a CBOR array
where each extension is represented with an int. The extensions
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mandated to be supported by [RFC7925] is encodeded as specified in
Section 3.2.
o signatureValue. Since the signature algorithm and resulting
signature length are known, padding and extra length fields which
are present in the ASN.1 encoding are omitted and the
'signatureValue' field is encoded as a CBOR byte string. For
natively signed CBOR certificates the signatureValue is calculated
over the certificate CBOR sequence excluding the signatureValue.
In addition to the above fields present in X.509, the CBOR encoding
introduces an additional field:
o type. A CBOR int used to indicate the type of CBOR certificate.
Currently, type can be a natively signed CBOR certificate (type =
0) or a CBOR compressed X.509 certificates (type = 1), see
Section 9.
The following Concise Data Definition Language (CDDL) defines
certificate and tbsCertificate as groups, which are encoded as CBOR
Sequences [RFC8742]. The member names therefore only have
documentary value.
certificate = (
tbsCertificate,
signatureValue : bytes,
)
tbsCertificate = (
type : int,
serialNumber : bytes,
signatureAlgorithm : int,
issuer : [ 2* DistinguishedName ] / DistinguishedName,
validity_notBefore: uint,
validity_notAfter: uint,
subject : [ 2* DistinguishedName ] / DistinguishedName,
subjectPublicKeyInfo_algorithm : int,
subjectPublicKeyInfo_subjectPublicKey : bytes,
extensions : [ 2* extension ] / extension,
)
DistinguishedName = { + int => bytes } / text / bytes
extension = (int, ? text / bytes)
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3.2. Encoding of Extensions
NOTE: The discussions in the COSE WG seems to indicate that a much
larger set of extensions should be supported. This will likely
result in a completly different encoding than the one below, which is
very [RFC7925] focused.
This section details the encoding of the 'extensions' field. Each
extension is represented with an int. Critical extensions are
encoded with a negative sign. The boolean values (digitalSignature,
keyAgreement, etc.) are set to 0 or 1 according to their value in the
DER encoding. If the array contains a single int, 'extensions' is
encoded as the int instead of an array. pathLenConstraint is limited
to a max value of 10. If subjectAltName is present, the value is
placed after the int the end of the array encoded as a byte or text
string following the encoding rules for the subject field.
subjectAltName = 1
basicConstraints = 2 + pathLenConstraint
keyUsage = 12 + digitalSignature
+ 2 * keyAgreement + 4 * keyCertSign
extKeyUsage = 19 + id-kp-serverAuth + 2 * id-kp-clientAuth
+ 4 * id-kp-codeSigning + 8 * id-kp-OCSPSigning
Consequently:
o A non-critical subjectAltName is encoded as 1. A critical
subjectAltName is encoded as -1.
o A critical basicConstraints (cA = 1) without pathLenConstraint is
encoded as -2.
o A non-critical keyUsage (digitalSignature = 0, keyAgreement = 1,
keyCertSign = 0) is encoded as 14 (= 12 + 2).
o A non-criticical extKeyUsage (id-kp-serverAuth = 0, id-kp-
clientAuth = 0, id-kp-codeSigning = 1, id-kp-OCSPSigning = 1) is
encoded as 31 (= 19 + 4 + 8).
Thus, a critical basicConstraints (cA = 1) followed by a non-critical
keyUsage (digitalSignature = 0, keyAgreement = 1, keyCertSign = 0) is
encoded as [-2, 14]. A single critical subjectAltName (dNSName =
"for.example") is encoded as [-1, "for.example"].
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4. Compliance Requirements for Constrained IoT
For general purpose applications, the normative requirements of
[RFC5280] applies. This section describes the mandatory to implement
algorithms and OIDs for constrained IoT application; the values of
the OIDs including certificate fields and extensions, time format,
attributes in distinguished names, etc.
TODO: Write this section
5. Deployment settings
CBOR certificates can be deployed with legacy X.509 certificates and
CA infrastructure. In order to verify the signature, the CBOR
certificate is used to recreate the original X.509 data structure to
be able to verify the signature.
For protocols like TLS/DTLS 1.2, where the handshake is sent
unencrypted, the actual encoding and compression can be done at
different locations depending on the deployment setting. For
example, the mapping between CBOR certificate and standard X.509
certificate can take place in a 6LoWPAN border gateway which allows
the server side to stay unmodified. This case gives the advantage of
the low overhead of a CBOR certificate over a constrained wireless
links. The conversion to X.509 within an IoT device will incur a
computational overhead, however, measured in energy this is
negligible compared to the reduced communication overhead.
For the setting with constrained server and server-only
authentication, the server only needs to be provisioned with the CBOR
certificate and does not perform the conversion to X.509. This
option is viable when client authentication can be asserted by other
means.
For protocols like IKEv2, TLS/DTLS 1.3, and EDHOC, where certificates
are encrypted, the proposed encoding needs to be done fully end-to-
end, through adding the encoding/decoding functionality to the
server.
6. Expected Certificate Sizes
The CBOR encoding of the sample certificate given in Appendix A
results in the numbers shown in Figure 1. After [RFC7925] profiling,
most duplicated information has been removed, and the remaining text
strings are minimal in size. Therefore the further size reduction
reached with general compression mechanisms will be small, mainly
corresponding to making the ASN.1 endcoding more compact. The zlib
number was calculated with zlib-flate.
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zlib-flate -compress < cert.der > cert.compressed
+------------------+--------------+------------+--------------------+
| | RFC 7925 | zlib | CBOR Certificate |
+------------------+---------------------------+--------------------+
| Certificate Size | 314 | 295 | 138 |
+------------------+--------------+------------+--------------------+
Figure 1: Comparing Sizes of Certificates (bytes)
7. Natively Signed CBOR Certificates
The difference between CBOR compressed X.509 certificate and natively
signed CBOR certificate is that the signature is calculated over the
CBOR encoding of the CBOR sequence tbsCertficate rather than the DER
encoded ASN.1 data. This removes entirely the need for ASN.1 DER and
base64 encoding which reduces the processing in the authenticating
devices, and avoids known complexities with these encodings.
Natively signed CBOR certificates can be applied in devices that are
only required to authenticate to natively signed CBOR certificate
compatible servers. This is not a major restriction for many IoT
deployments, where the parties issuing and verifying certificates can
be a restricted ecosystem which not necessarily involves public CAs.
CBOR compressed X.509 certificates provides an intermediate step
between [RFC7925] profiled X.509 certificates and natively signed
CBOR certificates: An implementation of CBOR compressed X.509
certificates contains both the CBOR encoding of the X.509 certificate
and the signature operations sufficient for natively signed CBOR
certificates.
8. Security Considerations
The CBOR profiling of X.509 certificates does not change the security
assumptions needed when deploying standard X.509 certificates but
decreases the number of fields transmitted, which reduces the risk
for implementation errors.
Conversion between the certificate formats can be made in constant
time to reduce risk of information leakage through side channels.
The mechanism in this draft does not reveal any additional
information compared to X.509. Because of difference in size, it
will be possible to detect that this profile is used. The gateway
solution described in Section 5 requires unencrypted certificates and
is not recommended.
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9. IANA Considerations
For all items, the 'Reference' field points to this document.
9.1. CBOR Certificate Types Registry
IANA has created a new registry titled "CBOR Certificate Types" under
the new heading "CBOR Certificate". The registration procedure is
"Expert Review". The columns of the registry are Value, Description,
and Reference, where Value is an integer and the other columns are
text strings. The initial contents of the registry are:
+-------+---------------------------------------+
| Value | Description |
+=======+=======================================+
| 0 | Natively Signed CBOR Certificate |
| 1 | CBOR Compressed X.509 Certificate |
+-------+---------------------------------------+
Figure 2: CBOR Certificate Types
9.2. CBOR Attribute Type Registry
IANA has created a new registry titled "CBOR Attribute Type Registry"
under the new heading "CBOR Certificate". The registration procedure
is "Expert Review". The columns of the registry are Value, X.509
Attribute Type, and Reference, where Value is an integer and the
other columns are text strings. The initial contents of the registry
are:
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+-------+---------------------------------------+
| Value | X.509 Attribute Type |
+=======+=======================================+
| 1 | id-at-countryName |
| 2 | id-at-organizationName |
| 3 | id-at-organizationalUnitName |
| 4 | id-at-dnQualifier |
| 5 | id-at-stateOrProvinceName |
| 6 | id-at-commonName |
| 7 | id-at-serialNumber |
| 8 | id-at-localityName |
| 9 | id-at-title |
| 10 | id-at-surname |
| 11 | id-at-givenName |
| 12 | id-at-initials |
| 13 | id-at-pseudonym |
| 14 | id-at-generationQualifier |
+-------+---------------------------------------+
Figure 3: CBOR Attribute Type Registry
9.3. CBOR Certificate Signature Algorithms Registry
IANA has created a new registry titled "CBOR Certificate Signature
Algorithms" under the new heading "CBOR Certificate". The
registration procedure is "Expert Review". The columns of the
registry are Value, X.509 Algorithm, and Reference, where Value is an
integer and the other columns are text strings. The initial contents
of the registry are:
+-------+---------------------------------------+
| Value | X.509 Signature Algorithm |
+=======+=======================================+
| 0 | ecdsa-with-SHA256 |
| 1 | ecdsa-with-SHA384 |
| 2 | ecdsa-with-SHA512 |
| 3 | id-ecdsa-with-shake128 |
| 4 | id-ecdsa-with-shake256 |
| 5 | id-Ed25519 |
| 6 | id-Ed448 |
+-------+---------------------------------------+
Figure 4: CBOR Certificate Signature Algorithms
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9.4. CBOR Certificate Public Key Algorithms Registry
IANA has created a new registry titled "CBOR Certificate Public Key
Algorithms" under the new heading "CBOR Certificate". The
registration procedure is "Expert Review". The columns of the
registry are Value, X.509 Algorithm, and Reference, where Value is an
integer and the other columns are text strings. The initial contents
of the registry are:
+-------+---------------------------------------+
| Value | X.509 Public Key Algorithm |
+=======+=======================================+
| 0 | id-ecPublicKey + prime256v1 |
| 1 | id-ecPublicKey + prime384v1 |
| 2 | id-ecPublicKey + prime512v1 |
| 3 | id-X25519 |
| 4 | id-X448 |
| 5 | id-Ed25519 |
| 6 | id-Ed448 |
+-------+---------------------------------------+
Figure 5: CBOR Certificate Public Key Algorithms
9.5. COSE Header Parameters Registry
This document registers the following entries in the "COSE Header
Parameters" registry under the "CBOR Object Signing and Encryption
(COSE)" heading. The formatting and processing are the same as the
corresponding x5chain and x5u defined in [I-D.ietf-cose-x509] except
that the certificates are CBOR encoded instead of DER encoded.
+-----------+-------+----------------+---------------------+
| Name | Label | Value Type | Description |
+===========+=======+================+=====================+
| CBORchain | TBD1 | COSE_CBOR_Cert | An ordered chain of |
| | | | CBOR certificates |
+-----------+-------+----------------+---------------------+
| CBORu | TBD2 | uri | URI pointing to a |
| | | | CBOR certificate |
+-----------+-------+----------------+---------------------+
9.6. TLS Certificate Compression Algorithm IDs Registry
This document registers the following entry in the "Certificate
Compression Algorithm IDs" registry under the "Transport Layer
Security (TLS) Extensions" heading.
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+------------------+------------------------------+
| Algorithm Number | Description |
+==================+==============================+
| TBD3 | CBOR Certificate |
+------------------+------------------------------+
10. References
10.1. Normative References
[I-D.ietf-tls-certificate-compression]
Ghedini, A. and V. Vasiliev, "TLS Certificate
Compression", draft-ietf-tls-certificate-compression-10
(work in progress), January 2020.
[I-D.ietf-tls-dtls13]
Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", draft-ietf-tls-dtls13-38 (work in progress), May
2020.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[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, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <https://www.rfc-editor.org/info/rfc7049>.
[RFC7925] Tschofenig, H., Ed. and T. Fossati, "Transport Layer
Security (TLS) / Datagram Transport Layer Security (DTLS)
Profiles for the Internet of Things", RFC 7925,
DOI 10.17487/RFC7925, July 2016,
<https://www.rfc-editor.org/info/rfc7925>.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/info/rfc8152>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/info/rfc8610>.
[RFC8742] Bormann, C., "Concise Binary Object Representation (CBOR)
Sequences", RFC 8742, DOI 10.17487/RFC8742, February 2020,
<https://www.rfc-editor.org/info/rfc8742>.
10.2. Informative References
[I-D.ietf-cose-x509]
Schaad, J., "CBOR Object Signing and Encryption (COSE):
Header parameters for carrying and referencing X.509
certificates", draft-ietf-cose-x509-07 (work in progress),
September 2020.
[I-D.ietf-lake-edhoc]
Selander, G., Mattsson, J., and F. Palombini, "Ephemeral
Diffie-Hellman Over COSE (EDHOC)", draft-ietf-lake-
edhoc-01 (work in progress), August 2020.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<https://www.rfc-editor.org/info/rfc7228>.
[SECG] "Elliptic Curve Cryptography, Standards for Efficient
Cryptography Group, ver. 2", 2009,
<https://secg.org/sec1-v2.pdf>.
[X.509-IoT]
Forsby, F., Furuhed, M., Papadimitratos, P., and S. Raza,
"Lightweight X.509 Digital Certificates for the Internet
of Things.", Springer, Cham. Lecture Notes of the
Institute for Computer Sciences, Social Informatics and
Telecommunications Engineering, vol 242., July 2018,
<https://doi.org/10.1007/978-3-319-93797-7_14>.
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Appendix A. Example CBOR Certificates
A.1. Example X.509 Certificate
Example of [RFC7925] profiled X.509 certificate parsed with OpenSSL.
Certificate:
Data:
Version: 3 (0x2)
Serial Number: 128269 (0x1f50d)
Signature Algorithm: ecdsa-with-SHA256
Issuer: CN=RFC test CA
Validity
Not Before: Jan 1 00:00:00 2020 GMT
Not After : Feb 2 00:00:00 2021 GMT
Subject: CN=01-23-45-FF-FE-67-89-AB
Subject Public Key Info:
Public Key Algorithm: id-ecPublicKey
Public-Key: (256 bit)
pub:
04:ae:4c:db:01:f6:14:de:fc:71:21:28:5f:dc:7f:
5c:6d:1d:42:c9:56:47:f0:61:ba:00:80:df:67:88:
67:84:5e:e9:a6:9f:d4:89:31:49:da:e3:d3:b1:54:
16:d7:53:2c:38:71:52:b8:0b:0d:f3:e1:af:40:8a:
95:d3:07:1e:58
ASN1 OID: prime256v1
NIST CURVE: P-256
X509v3 extensions:
X509v3 Key Usage:
Digital Signature
Signature Algorithm: ecdsa-with-SHA256
30:44:02:20:37:38:73:ef:87:81:b8:82:97:ef:23:5c:1f:ac:
cf:62:da:4e:44:74:0d:c2:a2:e6:a3:c6:c8:82:a3:23:8d:9c:
02:20:3a:d9:35:3b:a7:88:68:3b:06:bb:48:fe:ca:16:ea:71:
17:17:34:c6:75:c5:33:2b:2a:f1:cb:73:38:10:a1:fc
The DER encoding of the above certificate is 314 bytes.
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308201363081DEA003020102020301F50D300A06082A8648CE3D040302301631
14301206035504030C0B5246432074657374204341301E170D32303031303130
30303030305A170D3231303230323030303030305A30223120301E0603550403
0C1730312D32332D34352D46462D46452D36372D38392D41423059301306072A
8648CE3D020106082A8648CE3D03010703420004AE4CDB01F614DEFC7121285F
DC7F5C6D1D42C95647F061BA0080DF678867845EE9A69FD4893149DAE3D3B154
16D7532C387152B80B0DF3E1AF408A95D3071E58A30F300D300B0603551D0F04
0403020780300A06082A8648CE3D04030203470030440220373873EF8781B882
97EF235C1FACCF62DA4E44740DC2A2E6A3C6C882A3238D9C02203AD9353BA788
683B06BB48FECA16EA71171734C675C5332B2AF1CB733810A1FC
A.2. Example CBOR Certificate Compression
The CBOR certificate compression of the X.509 in CBOR diagnostic
format is:
(
1,
h'01f50d',
0,
"RFC test CA",
721699200,
760492800,
h'0123456789AB',
0,
h'02ae4cdb01f614defc7121285fdc7f5c6d1d42c95647f061ba
0080df678867845e',
5,
h'373873EF8781B88297EF235C1FACCF62DA4E44740DC2A2E6A3
C6C882A3238D9C3AD9353BA788683B06BB48FECA16EA711717
34C675C5332B2AF1CB733810A1FC'
)
The CBOR encoding (CBOR sequence) of the CBOR certificate is 138
bytes.
014301F50D006B52464320746573742043411A2B0441801A2D54330046012345
6789AB00582102AE4CDB01F614DEFC7121285FDC7F5C6D1D42C95647F061BA00
80DF678867845E055840373873EF8781B88297EF235C1FACCF62DA4E44740DC2
A2E6A3C6C882A3238D9C3AD9353BA788683B06BB48FECA16EA71171734C675C5
332B2AF1CB733810A1FC
A.3. Example: Natively Signed CBOR Certificate
The corresponding natively signed CBOR certificate in CBOR diagnostic
format is identical except for type and signatureValue.
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(
0,
h'01f50d',
0,
"RFC test CA",
721699200,
760492800,
h'0123456789AB',
0,
h'02ae4cdb01f614defc7121285fdc7f5c6d1d42c95647f061
ba0080df678867845e',
5,
h'7F10A063DA8DB2FD49414440CDF85070AC22A266C7F1DFB1
577D9A35A295A8742E794258B76968C097F85542322A0796
0199C13CC0220A9BC729EF2ECA638CFE'
)
The CBOR encoding (CBOR sequence) of the CBOR certificate is 138
bytes.
004301F50D006B52464320746573742043411A2B0441801A2D54330046012345
6789AB00582102AE4CDB01F614DEFC7121285FDC7F5C6D1D42C95647F061BA00
80DF678867845E0558407F10A063DA8DB2FD49414440CDF85070AC22A266C7F1
DFB1577D9A35A295A8742E794258B76968C097F85542322A07960199C13CC022
0A9BC729EF2ECA638CFE
Appendix B. X.509 Certificate Profile, ASN.1
NOTE: The ASN.1 below is not up to date with the rest of the
specification
TODO - This ASN.1 profile should probably be in a document that
updates RFC 7925.
IOTCertificate DEFINITIONS EXPLICIT TAGS ::= BEGIN
Certificate ::= SEQUENCE {
tbsCertificate TBSCertificate,
signatureAlgorithm AlgorithmIdentifier,
signatureValue BIT STRING
}
TBSCertificate ::= SEQUENCE {
version [0] INTEGER {v3(2)},
serialNumber INTEGER (1..MAX),
signature AlgorithmIdentifier,
issuer Name,
validity Validity,
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subject Name,
subjectPublicKeyInfo SubjectPublicKeyInfo,
extensions [3] Extensions OPTIONAL
}
Name ::= SEQUENCE SIZE (1) OF DistinguishedName
DistinguishedName ::= SET SIZE (1) OF CommonName
CommonName ::= SEQUENCE {
type OBJECT IDENTIFIER (id-at-commonName),
value UTF8String
}
Validity ::= SEQUENCE {
notBefore UTCTime,
notAfter UTCTime
}
SubjectPublicKeyInfo ::= SEQUENCE {
algorithm AlgorithmIdentifier,
subjectPublicKey BIT STRING
}
AlgorithmIdentifier ::= SEQUENCE {
algorithm OBJECT IDENTIFIER,
parameters ANY DEFINED BY algorithm OPTIONAL }
}
Extensions ::= SEQUENCE SIZE (1..MAX) OF Extension
Extension ::= SEQUENCE {
extnId OBJECT IDENTIFIER,
critical BOOLEAN DEFAULT FALSE,
extnValue OCTET STRING
}
id-at-commonName OBJECT IDENTIFIER ::=
{joint-iso-itu-t(2) ds(5) attributeType(4) 3}
END
Authors' Addresses
Shahid Raza
RISE AB
Email: shahid.raza@ri.se
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Joel Hoeglund
RISE AB
Email: joel.hoglund@ri.se
Goeran Selander
Ericsson AB
Email: goran.selander@ericsson.com
John Preuss Mattsson
Ericsson AB
Email: john.mattsson@ericsson.com
Martin Furuhed
Nexus Group
Email: martin.furuhed@nexusgroup.com
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