One document matched: draft-schaad-cose-01.xml
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<rfc ipr="trust200902" docName="draft-schaad-cose-01" category="info">
<front>
<title>CBOR Encoded Message Syntax</title>
<author initials="J." surname="Schaad" fullname="Jim Schaad">
<organization>August Cellars</organization>
<address>
<email>ietf@augustcellars.com</email>
</address>
</author>
<date year="2015" month="April" day="21"/>
<area>Security</area>
<abstract>
<t>Concise Binary Object Representation (CBOR) is data format designed for small code size and small message size.
There is a need for the ability to have the basic security services defined for this data format.
This document specifies how to do signatures, message authentication codes and encryption using this data format.
The work in this document is derived in part from the JSON web security documents using the same parameters and algorithm identifiers as they do.</t>
</abstract>
</front>
<middle>
<section anchor="introduction" title="Introduction">
<t>The JOSE working group produced a set of documents that defined how to
perform encryption, signatures and message authentication (MAC)
operations for JavaScript Object Notation (JSON) documents and then to encode the results using the
JSON format <xref target="RFC7159"/>.
This document does the same work for use with the Concise Binary Object Representation (CBOR) <xref target="RFC7049"/> document format.
While there is a strong attempt to keep the flavor of the original
JOSE documents, two considerations are taking into account:</t>
<t><list style="symbols">
<t>CBOR has capabilities that are not present in JSON and should be used.
One example of this is the fact that CBOR has a method of encoding binary directly without first converting it into a base64 encoded sting.</t>
<t>The authors did not always agree with some of the decisions made by the JOSE working group.
Many of these decisions have been re-examined, and where it seems to the authors to be superior or simpler, replaced.</t>
</list></t>
<section anchor="design-changes-from-jose" title="Design changes from JOSE">
<t><list style="symbols">
<t>Define a top level message structure so that encrypted, signed and MAC-ed messages can easily identified and still have a consistent view.</t>
<t>Switch from using a map to using an array at the message level.
While this change means that it is no longer possible to add new named parameters to
the top level message, it also means that there is not a need to define how older
implementations are defined to behave when new fields are present.
Most of the reasons that a new field would need to be defined are adequately addressed
by defining a new parameter instead.</t>
<t>Signed messages separate the concept of protected and unprotected attributes that are for the content and the signature.</t>
<t>Key management has been made to be more uniform. All key management techniques are represented as a recipient rather than only have some of them be so.</t>
<t>MAC messages are separated from signed messages.</t>
<t>MAC messages have the ability to do key management on the MAC key.</t>
<t>Use binary encodings for binary data rather than base64url encodings.</t>
<t>Remove the authentiction tag for encryption algorithms as a separate item.</t>
</list></t>
</section>
<section anchor="requirements-terminology" title="Requirements Terminology">
<t>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 <xref target="RFC2119"/>.</t>
<t>When the words appear in lower case, their natural language meaning is used.</t>
</section>
<section anchor="cbor-grammar" title="CBOR Grammar">
<t>There currently is no standard CBOR grammar available for use by
specifications.
In this document, we use the grammar defined in the CBOR data
definition language (CDDL)
<xref target="I-D.greevenbosch-appsawg-cbor-cddl"/>.</t>
</section>
</section>
<section anchor="the-cosemsg-structure" title="The COSE_MSG structure">
<t>The COSE_MSG structure is a top level CBOR object which corresponds to
the DataContent type in <xref target="RFC5652"/>.
This structure allows for a top level message to be sent which could
be any of the different security services, where the security service
is identified.
The presence of this structure does not preclude a protocol to use one
of the individual structures as a stand alone component.</t>
<figure><artwork type="CDDL"><![CDATA[
COSE_MSG = [sign:1, COSE_Sign] /
[encrypt:2, COSE_encrypt] /
[mac:3, COSE_mac]
]]></artwork></figure>
<t>The top level of each of the COSE message structures are encoded as arrays.<vspace />
We use an integer to distingish bettwen the different security message types.
By looking at the integer in the first element, one can determine which security message is
being used and thus what the syntax is for the rest of the elements in the array.</t>
<t>Implementations SHOULD be prepared to find an integer in the location which does not correspond to the values 0 to 2.
If this is found then the client MUST stop attempting to parse the structure and fail.
Clients need to recognize that the set of values could be extended at a later date, but should not provide a security service based on guesses of what is there.</t>
<t>NOTE: Alternative syntax with tags would be</t>
<figure><artwork><![CDATA[
COSE_MSG = COSE_SignedMessage /
#6.998([COSE_encrypt]) /
#6.999([COSE_mac])
]]></artwork></figure>
<t>Where we would need to define the latter two as tagged arrays like is currently done for COSE_SignedMessage.<vspace />
There is no space savings in CBOR, this is strictly about using CBOR paradymes. It is not clear what would happen if a JOSE serialization appeared, but that is probably not interesting.
If this path is used, then there is no extensibility for new messages types. They would need to be defined on their own.</t>
</section>
<section anchor="signing-structure" title="Signing Structure">
<t>The signature structure allows for one or more signatures to be applied to a message payload.
There are provisions for attributes about the content and attributes about the signature to be
carried along with the signature itself.
These attributes may be authenticated by the signature, or just present.
Examples of attributes about the content would be the type of content, when the content
was created, and who created the content.
Examples of attributes about the signature would be the algorithm and key used to create
the signature, when the signature was created, and counter-signatures.</t>
<t>When more than one signature is present, the successful validation of
one signature associated with a given signer is usually treated as a
successful signature by that signer. However, there are some
application environments where other rules are needed. An
application that employs a rule other than one valid signature for
each signer must specify those rules. Also, where simple matching of
the signer identifier is not sufficient to determine whether the
signatures were generated by the same signer, the application
specification must describe how to determine which signatures were
generated by the same signer. Support of different communities of
recipients is the primary reason that signers choose to include more
than one signature. For example, the COSE_Sign structure might
include signatures generated with the RSA signature algorithm and
with the Elliptic Curve Digital Signature Algorithm (ECDSA) signature
algorithm. This allows recipients to verify the signature associated
with one algorithm or the other. (Source of text is <xref target="RFC5652"/>.)
More detailed information on multiple signature evaluation can be found in <xref target="RFC5752"/>.</t>
<t>The CDDL grammar structure for a signature message is:</t>
<figure><artwork type="CDDL"><![CDATA[
COSE_Sign = (
protected : (bstr / nil),
unprotected : (header_map / nil),
payload : (bstr / nil),
? signatures: ([+[COSE_signature]] / nil),
? COSE_signature
)
COSE_SignMessage = #6.997([ COSE_Sign ])
keys = int / tstr
header_map = {+ keys => any }
]]></artwork></figure>
<t>The fields is the structure have the following semantics:</t>
<t><list style="hanging">
<t hangText='protected'>
contains attributes about the payload which are to be protected by the signature.
An example of such an attribute would be the content type (‘cty’) attribute.
The content is a CBOR map of attributes which is encoded to a byte stream.
This field MUST NOT contain attributes about the signature, even if
those attributes are common across multiple signatures.</t>
<t hangText='unprotected'>
contains attributes about the payload which are not protected by the signature.
An example of such an attribute would be the content type (‘cty’) attribute.
This field MUST NOT contain attributes about a signature, even if
the attributes are common across multiple signatures.</t>
<t hangText='payload'>
contains the serialized content to be signed.<vspace />
If the payload is not present in the message, the application is required to
supply the payload separately.<vspace />
The payload is wrapped in a bstr to ensure that it is transported without changes,
if the payload is transported separately it is the responsibility of the application
to ensure that it will be transported without changes.</t>
<t hangText='signatures'>
is either a single signature or an array of signature values.<vspace />
A single signature value can be represented using either data type.
Implementations MUST be able to parse both data types.</t>
</list></t>
<t>The CDDL grammar structure for a signature is:</t>
<figure><artwork type="CDDL"><![CDATA[
COSE_signature = (
protected : (bstr / nil),
unprotected : (header_map / nil),
signature : bstr
)
]]></artwork></figure>
<t>The fields in the structure have the following semantics:</t>
<t><list style="hanging">
<t hangText='protected'>
contains additional information to be authenticated by the signature.
The field holds data about the signature operation.
The field MUST NOT hold attributes about the payload being signed.
The content is a CBOR map of attributes which is encoded to a byte stream.
At least one of protected and unprotected MUST be present.</t>
<t hangText='unprotected'>
contains attributes about the signature which are not protected by the signature.
This field MUST NOT contain attributes about the payload being signed.
At least one of protected and unprotected MUST be present.</t>
<t hangText='signature'>
contains the computed signature value.</t>
</list></t>
<t>The COSE structure used to create the byte stream to be signed uses the following CDDL grammar structure:</t>
<figure><artwork type="CDDL"><![CDATA[
Sig_structure = [
body_protected : (bstr / nil),
sign_protected : (bstr / nil),
payload : bstr
]
]]></artwork></figure>
<t>How to compute a signature:</t>
<t><list style="numbers">
<t>Create a Sig_structure object and populate it with the appropriate fields.</t>
<t>Create the value to be hashed by encoding the Sig_structure to a byte string.</t>
<t>Comput the hash value from the byte string.</t>
<t>Sign the hash</t>
<t>Place the signature value into the appropriate signature field.</t>
</list></t>
</section>
<section anchor="encryption-object" title="Encryption object">
<t>In this section we describe the structure and methods to be used when
doing an encryption in COSE.
In COSE, we use the same techniques and structures for encrypting both
the plain text and the keys used to protect the text.
This is different from the approach used by both <xref target="RFC5652"/> and
<xref target="I-D.ietf-jose-json-web-encryption"/> where different structures are
used for the plain text and for the different key management
techniques.</t>
<t>One of the byproducts of using the same technique for encrypting and
encoding both the content and the keys using the various key management
techniques, is a requirement that all of the key management techniques
use an Authenticated Encryption (AE) algorithm. (For the purpose of this document we use a slightly loose definition of AE algorithms.)
When encrypting the plain text, it is normal to use an Authenticated
Encryption with Additional Data (AEAD) algorithm. For key management,
either AE or AEAD algorithms can be used.
See <xref target="AE-algo"/> for more details about the different types of
algorithms.</t>
<t>The CDDL grammar structure for encryption is:</t>
<figure><artwork type="CDDL"><![CDATA[
COSE_encrypt = (
protected : (bstr / nil), ; Contains header_map
unprotected : (header_map / nil),
iv : (bstr / nil),
aad : (bstr / nil),
ciphertext : (bstr / nil),
? recipients : ([+COSE_encrypt_a] / nil)
? COSE_encrypt
)
COSE_encrypt_a = [COSE_encrypt]
]]></artwork></figure>
<t>Description of the fields:</t>
<t><list style="hanging">
<t hangText='protected'>
contains the information about the plain text or encryption
process that is to be integrity protected.
The field is encoded in CBOR as a ‘bstr’ if present and the value
‘nil’ if there is no data.
The contents of the protected field is a CBOR map of the protected
data names and values.
The map is CBOR encoded before placing it into the bstr.
Only values associated with the current cipher text are to be placed in this location even if the value would apply to multiple recipient structures.</t>
<t hangText='unprotected'>
contains information about the plain text that is not integrity protected.
If there are no field, then the value ‘nil’ is used.
Only values associated with the current cipher text are to be placed in this location even if the value would apply to multiple recipient structures.</t>
<t hangText='iv'>
contains the initialization vector (IV), or it’s equivalent, if one
is needed by the encryption algorithm.
If there is no IV, then the value ‘nil’ is used.</t>
<t hangText='aad'>
contains additional authenticated data (aad) supplied by the application.
This field contains information about the plain text data that is
authenticated, but not encrypted.
If the application does not provide this data, the value ‘nil’ is used.</t>
<t hangText='cipherText'>
contains the encrypted plain text.
If the cipherText is to be transported independently of the control
information about the encryption process (i.e. detached content)
then the value ‘nil’ is encoded here.</t>
<t hangText='recipients'>
contains the recipient information.
The field can have one of three data types:</t>
</list></t>
<t><list style="symbols">
<t>An array of COSE_encrypt elements, one for each recipient.</t>
<t>A single COSE_encrypt element, encoded as an extension to the containing COSE_encrypt element, for a single recipient.
Single recipients can be encoded either this way or as a single array element.</t>
<t>A ‘nil’ value if there are no recipients.</t>
</list></t>
<section anchor="key-management-methods" title="Key Management Methods">
<t>There are a number of different key management methods that can be
used in the COSE encryption system.
In this section we will discuss each of the key management methods and
what fields need to be specified to deal with each of them.</t>
<t>The names of the key management methods used here are the same as are
defined in <xref target="I-D.ietf-jose-json-web-key"/>.
Other specifications use different terms for the key management
methods or do not support some of the key management methods.</t>
<t>At the moment we do not have any key management methods that allow for the use of protected headers. This may be changed in the future if, for example, the AES-GCM Key wrap method defined in <xref target="I-D.ietf-jose-json-web-algorithms"/> were extended to allow for authenticated data. In that event the use of the ‘protected’ field, which is current forbidden below, would be permitted.</t>
<section anchor="direct-encryption" title="Direct Encryption">
<t>In direct encryption mode, a shared secret between the sender and the
recipient is used as the CEK.
When direct encryption mode is used, it MUST be the only mode used on the message.
It is a massive security leak to have both direct encryption and a
different key management mode on the same message.</t>
<t>For JOSE, direct encryption key management is the only key management
method allowed for doing MAC-ed messages.
In COSE, all of the key management methods can be used for MAC-ed messages.</t>
<t>The COSE_encrypt structure for the recipient is organized as follows:</t>
<t><list style="symbols">
<t>The ‘protected’, ‘iv’, ‘aad’, ‘ciphertext’ and ‘recipients’ fields
MUST be nil.</t>
<t>At a minimum, the ‘unprotected’ field SHOULD contain the ‘alg’
parameter as well as a parameter identifying the shared secret.</t>
</list></t>
</section>
<section anchor="key-wrapping" title="Key Wrapping">
<t>In key wrapping mode, the CEK is randomly generated and that key is
then encrypted by a shared secret between the sender and the
recipient.
All of the currently defined key wrapping algorithms for JOSE (and
thus for COSE) are AE algorithms.
Key wrapping mode is considered to be superior to direct encryption if
the system has any capability for doing random key generation.
This is because the shared key is used to wrap random data rather than
data has some degree of organization and may in fact be repeating the
same content.</t>
<t>The COSE_encrypt structure for the recipient is organized as follows:</t>
<t><list style="symbols">
<t>The ‘protected’, ‘aad’, and ‘recipients’ fields MUST be nil.</t>
<t>The plain text to be encrypted is the key from next layer down
(usually the content layer).</t>
<t>At a minimum, the ‘unprotected’ field SHOULD contain the ‘alg’
parameter as well as a parameter identifying the shared secret.</t>
<t>Use of the ‘iv’ field will depend on the key wrap algorithm.</t>
</list></t>
</section>
<section anchor="key-encryption" title="Key Encryption">
<t>Key Encryption mode is also called key transport mode in some
standards.
Key Encryption mode differs from Key Wrap mode in that it uses an
asymmetric encryption algorithm rather than a symmetric encryption
algorithm to protect the key.
The only current Key Encryption mode algorithm supported is RSAES-OAEP.</t>
<t>The COSE_encrypt structure for the recipient is organized as follows:</t>
<t><list style="symbols">
<t>The ‘protected’, ‘aad’, and ‘iv’ fields all use the ‘nil’ value.</t>
<t>The plain text to be encrypted is the key from next layer down
(usually the content layer).</t>
<t>At a minimum, the ‘unprotected’ field SHOULD contain the ‘alg’
parameter as well as a parameter identifying the asymmetric key.</t>
</list></t>
</section>
<section anchor="direct-key-agreement" title="Direct Key Agreement">
<t>Direct Key Agreement derives the CEK from the shared secret computed
by the key agreement operation.</t>
<t>When direct key agreement mode is used, it SHOULD be the only mode used
on the message. This method creates the CEK directly and that makes it difficult to mix with additional recipients.</t>
<t>The COSE_encrypt structure for the recipient is organized as follows:</t>
<t><list style="symbols">
<t>The ‘protected’, ‘aad’, and ‘iv’ fields all use the ‘nil’ value.</t>
<t>At a minimum, the ‘unprotected’ field SHOULD contain the ‘alg’
parameter as well as a parameter identifying the asymmetric key.</t>
<t>The ‘unprotected’ field MUST contain the ‘epk’ parameter.</t>
</list></t>
</section>
<section anchor="key-agreement-with-key-wrapping" title="Key Agreement with Key Wrapping">
<t>Key Agreement with Key Wrapping uses a randomly generated CEK.
The CEK is then encrypted using a Key Wrapping algorithm and a key
derived from the shared secret computed by the key agreement
algorithm.</t>
<t>The COSE_encrypt structure for the recipient is organized as follows:</t>
<t><list style="symbols">
<t>The ‘protected’, ‘aad’, and ‘iv’ fields all use the ‘nil’ value.</t>
<t>The plain text to be encrypted is the key from next layer down
(usually the content layer).</t>
<t>At a minimum, the ‘unprotected’ field SHOULD contain the ‘alg’
parameter, a parameter identifying the recipient asymmetric key, and
a parameter with the sender’s asymmetric public key.</t>
</list></t>
</section>
</section>
<section anchor="encryption-algorithm-for-aead-algorithms" title="Encryption Algorithm for AEAD algorithms">
<t>The encryption algorithm for AEAD algorithms is fairly simple.<vspace />
In order to get a consistent encoding of the data to be authenticated, the Enc_structure is used to have canonical form of the AAD.</t>
<figure><artwork type="CDDL"><![CDATA[
Enc_structure = [
protected : (bstr / nil),
aad : (bstr / nil)
]
]]></artwork></figure>
<t><list style="numbers">
<t>If there is protected data, CBOR encode the map to a byte string and place in the protected field of the Enc_structure and the COSE_Encrypt structure.</t>
<t>Copy the ‘aad’ field from the COSE_Encrypt structure to the Enc_Structure.</t>
<t>Encode the Enc_structure using a CBOR Canonical encoding <xref target="CBOR-Canonical"/> to get the AAD value.</t>
<t>Encrypt the plain text and place it in the ‘ciphertext’ field. The
AAD value is passed in as part of the encryption process.</t>
<t>For recipient of the message, recursively perform the encryption
algorithm for that recipient using the encryption key as the
plain text.</t>
</list></t>
</section>
<section anchor="encryption-algorithm-for-ae-algorithms" title="Encryption algorithm for AE algorithms">
<t><list style="numbers">
<t>Verify that the ‘protected’ field is empty.</t>
<t>Verify that the ‘aad’ field is empty.</t>
<t>Encrypt the plain text and place in the ‘ciphertext’ field.</t>
</list></t>
</section>
</section>
<section anchor="mac-objects" title="MAC objects">
<t>In this section we describe the structure and methods to be used when doing MAC authentication in COSE. JOSE used a variant of the signature structure for doing MAC operations and it is restricted to using a single pre-shared secret to do the authentication. This document allows for the use of all of the same methods of key management as are allowed for encryption.</t>
<t>When using MAC operations, there are two modes in which it can be used. The first is just a check that the content has not been changed since the MAC was computed. Any of the key management methods can be used for this purpose. The second mode is to both check that the content has not been changed since the MAC was computed, and to use key management to verify who sent it. The key management modes that support this are ones that either use a pre-shared secret, or do static-static key agreement. In both of these cases the entity MAC-ing the message can be validated by a key binding. (The binding of identity assumes that there are only two parties involved and you did not send the message yourself.)</t>
<figure><artwork type="CDDL"><![CDATA[
COSE_mac = (
protected : (bstr / nil),
unprotected : (header_map / nil),
payload : bstr,
tag : bstr,
?recipients : ([+COSE_encrypt_a] / nil)
? COSE_encrypt
)
]]></artwork></figure>
<t>Field descriptions:</t>
<t><list style="hanging">
<t hangText='protected'>
contains attributes about the payload which are to be protected by the MAC.
An example of such an attribute would be the content type (‘cty’) attribute.
The content is a CBOR map of attributes which is encoded to a byte stream.
This field MUST NOT contain attributes about the recipient, even if
those attributes are common across multiple recipients.
At least one of protected and unprotected MUST be present.</t>
<t hangText='unprotected'>
contains attributes about the payload which are not protected by the MAC.
An example of such an attribute would be the content type (‘cty’) attribute.
This field MUST NOT contain attributes about a recipient, even if
the attributes are common across multiple recipients.
At least one of protected and unprotected MUST be present.</t>
<t hangText='payload'>
contains the serialized content to be MAC-ed.<vspace />
If the payload is not present in the message, the application is required to supply the payload separately.<vspace />
The payload is wrapped in a bstr to ensure that it is transported without changes, if the payload is transported separately it is the responsibility of the application to ensure that it will be transported without changes.</t>
<t hangText='tag'>
contains the MAC value.</t>
<t hangText='recipients'>
contains the recipient information. See the description under COSE_Encryption for more info.</t>
</list></t>
<figure><artwork type="CDDL"><![CDATA[
MAC_structure = {
protected : (bstr / nil),
payload : bstr
}
]]></artwork></figure>
<t>How to compute a MAC:</t>
<t><list style="numbers">
<t>Create a MAC_structure and copy the protected and payload elements from the COSE_mac structure.</t>
<t>Encode the MAC_structure using a canonical CBOR encoder. The resulting bytes is the value to compute the MAC on.</t>
<t>Compute the MAC and place the result in the ‘tag’ field of the COSE_mac structure.</t>
<t>Encrypt and encode the MAC key for each recipient of the message.</t>
</list></t>
</section>
<section anchor="key-structure" title="Key Structure">
<t>There are only a few changes between JOSE and COSE for how keys are formatted.
As with JOSE, COSE uses a map to contain the elements of a key.
Those values, which in JOSE, are base64url encoded because they are binary values, are encoded as bstr values in COSE.</t>
<t>For COSE we use the same set of fields that were defined in
<xref target="I-D.ietf-jose-json-web-key"/>.</t>
<figure><artwork type="CDDL"><![CDATA[
COSE_Key = {
"kty" : tstr,
? "use" : tstr,
? "key_ops" : [+tstr],
? "alg" : tstr,
? "kid" : tstr,
* keys => values
}
COSE_KeySet = [+COSE_Key]
]]></artwork></figure>
<t>The element “kty” is a required element in a COSE_Key map.<vspace />
All other elements are optional and not all of the elements listed in <xref target="I-D.ietf-jose-json-web-key"/> or <xref target="I-D.ietf-jose-json-web-algorithms"/> have been listed here even though they can all appear in a COSE_Key map.</t>
<t>The “key_ops” element is prefered over the “use” element as the information provided that way is more finely detailed about the operations allowed. It is strongly suggested that this element be present for all keys.</t>
<t>The same fields defined in <xref target="I-D.ietf-jose-json-web-key"/> are used
here with the following changes in rules:</t>
<t><list style="symbols">
<t>Any item which is base64 encoded in JWK, is bstr encoded for COSE.</t>
<t>Any item which is integer encoded in JWK, is int encoded for COSE.</t>
<t><list style="hanging">
<t hangText='Any item which is string (but not base64) encoded in JWK, is tstr encoded for COSE.'>
</t>
<t hangText='Exceptions to this are the following fields:'>
</t>
<t hangText='kid'>
is always bstr encoded rather than tstr encoded.
This change in encoded is due to the fact that frequently, values
such as a hash of the public key is used for a kid value.
Since the field is defined as not having a specific structure,
making it binary rather than textual makes sense.</t>
</list></t>
</list></t>
</section>
<section anchor="CBOR-Canonical" title="CBOR Encoder Restrictions">
<t>There as been an attempt to resrict the number of places where the document
needs to impose restrictions on how the CBOR Encoder needs to work. We have
managed to narrow it down to the following restrictions:</t>
<t><list style="symbols">
<t>The restriction applies to the encoding the Sig_structure, the Enc_structure, and the MAC_structure.</t>
<t>The rules for Canonical CBOR (Section 3.9 of RFC 7049) MUST be used in these
locations. The main rule that needs to be enforced is that all lengths
in these structures MUST be encoded such that they are encoded using definite lengths
and the minimum length encoding is used.</t>
<t>All parsers used SHOULD fail on both parsing and generation if the same key is used twice in a map.</t>
</list></t>
</section>
<section anchor="iana-considerations" title="IANA Considerations">
<t>There are IANA considerations to be filled in.</t>
</section>
<section anchor="security-considerations" title="Security Considerations">
<t>There are security considerations:</t>
<t><list style="numbers">
<t>Protect private keys</t>
<t>MAC messages with more than one recipient means one cannot figure out who sent the message</t>
<t>Use of direct key with other recipient structures hands the key to other recipients.</t>
<t>Use of direcct ECDH direct encryption is easy for people to leak information on if there are other recipients in the message.</t>
<t>Considerations about protected vs unprotected header fields.</t>
</list></t>
</section>
</middle>
<back>
<references title='Normative References'>
<reference anchor='I-D.greevenbosch-appsawg-cbor-cddl'>
<front>
<title>CBOR data definition language: a notational convention to express CBOR data structures.</title>
<author initials='C' surname='Vigano' fullname='Christoph Vigano'>
<organization />
</author>
<author initials='H' surname='Birkholz' fullname='Henk Birkholz'>
<organization />
</author>
<author initials='R' surname='Sun' fullname='Ruinan Sun'>
<organization />
</author>
<date month='March' day='9' year='2015' />
<abstract><t>This document proposes a notational convention to express CBOR data structures (RFC 7049). Its main goal is to provide an easy and unambiguous way to express structures for protocol messages and data formats that use CBOR.</t></abstract>
</front>
<seriesInfo name='Internet-Draft' value='draft-greevenbosch-appsawg-cbor-cddl-05' />
<format type='TXT'
target='http://www.ietf.org/internet-drafts/draft-greevenbosch-appsawg-cbor-cddl-05.txt' />
</reference>
<reference anchor='I-D.ietf-jose-json-web-algorithms'>
<front>
<title>JSON Web Algorithms (JWA)</title>
<author initials='M' surname='Jones' fullname='Michael Jones'>
<organization />
</author>
<date month='January' day='13' year='2015' />
<abstract><t>The JSON Web Algorithms (JWA) specification registers cryptographic algorithms and identifiers to be used with the JSON Web Signature (JWS), JSON Web Encryption (JWE), and JSON Web Key (JWK) specifications. It defines several IANA registries for these identifiers.</t></abstract>
</front>
<seriesInfo name='Internet-Draft' value='draft-ietf-jose-json-web-algorithms-40' />
<format type='TXT'
target='http://www.ietf.org/internet-drafts/draft-ietf-jose-json-web-algorithms-40.txt' />
</reference>
<reference anchor='RFC7049'>
<front>
<title>Concise Binary Object Representation (CBOR)</title>
<author initials='C.' surname='Bormann' fullname='C. Bormann'>
<organization /></author>
<author initials='P.' surname='Hoffman' fullname='P. Hoffman'>
<organization /></author>
<date year='2013' month='October' />
<abstract>
<t>The Concise Binary Object Representation (CBOR) is a data format whose design goals include the possibility of extremely small code size, fairly small message size, and extensibility without the need for version negotiation. These design goals make it different from earlier binary serializations such as ASN.1 and MessagePack.</t></abstract></front>
<seriesInfo name='RFC' value='7049' />
<format type='TXT' octets='134062' target='http://www.rfc-editor.org/rfc/rfc7049.txt' />
</reference>
</references>
<references title='Informative References'>
<reference anchor='I-D.ietf-jose-json-web-encryption'>
<front>
<title>JSON Web Encryption (JWE)</title>
<author initials='M' surname='Jones' fullname='Michael Jones'>
<organization />
</author>
<author initials='J' surname='Hildebrand' fullname='Joe Hildebrand'>
<organization />
</author>
<date month='January' day='13' year='2015' />
<abstract><t>JSON Web Encryption (JWE) represents encrypted content using JavaScript Object Notation (JSON) based data structures. Cryptographic algorithms and identifiers for use with this specification are described in the separate JSON Web Algorithms (JWA) specification and IANA registries defined by that specification. Related digital signature and MAC capabilities are described in the separate JSON Web Signature (JWS) specification.</t></abstract>
</front>
<seriesInfo name='Internet-Draft' value='draft-ietf-jose-json-web-encryption-40' />
<format type='TXT'
target='http://www.ietf.org/internet-drafts/draft-ietf-jose-json-web-encryption-40.txt' />
</reference>
<reference anchor='I-D.ietf-jose-json-web-signature'>
<front>
<title>JSON Web Signature (JWS)</title>
<author initials='M' surname='Jones' fullname='Michael Jones'>
<organization />
</author>
<author initials='J' surname='Bradley' fullname='John Bradley'>
<organization />
</author>
<author initials='N' surname='Sakimura' fullname='Nat Sakimura'>
<organization />
</author>
<date month='January' day='16' year='2015' />
<abstract><t>JSON Web Signature (JWS) represents content secured with digital signatures or Message Authentication Codes (MACs) using JavaScript Object Notation (JSON) based data structures. Cryptographic algorithms and identifiers for use with this specification are described in the separate JSON Web Algorithms (JWA) specification and an IANA registry defined by that specification. Related encryption capabilities are described in the separate JSON Web Encryption (JWE) specification.</t></abstract>
</front>
<seriesInfo name='Internet-Draft' value='draft-ietf-jose-json-web-signature-41' />
<format type='TXT'
target='http://www.ietf.org/internet-drafts/draft-ietf-jose-json-web-signature-41.txt' />
</reference>
<reference anchor='I-D.ietf-jose-json-web-key'>
<front>
<title>JSON Web Key (JWK)</title>
<author initials='M' surname='Jones' fullname='Michael Jones'>
<organization />
</author>
<date month='January' day='16' year='2015' />
<abstract><t>A JSON Web Key (JWK) is a JavaScript Object Notation (JSON) data structure that represents a cryptographic key. This specification also defines a JSON Web Key Set (JWK Set) JSON data structure that represents a set of JWKs. Cryptographic algorithms and identifiers for use with this specification are described in the separate JSON Web Algorithms (JWA) specification and IANA registries defined by that specification.</t></abstract>
</front>
<seriesInfo name='Internet-Draft' value='draft-ietf-jose-json-web-key-41' />
<format type='TXT'
target='http://www.ietf.org/internet-drafts/draft-ietf-jose-json-web-key-41.txt' />
</reference>
<reference anchor='I-D.mcgrew-aead-aes-cbc-hmac-sha2'>
<front>
<title>Authenticated Encryption with AES-CBC and HMAC-SHA</title>
<author initials='D' surname='McGrew' fullname='David McGrew'>
<organization />
</author>
<author initials='J' surname='Foley' fullname='John Foley'>
<organization />
</author>
<author initials='K' surname='Paterson' fullname='Kenny Paterson'>
<organization />
</author>
<date month='July' day='4' year='2014' />
<abstract><t>This document specifies algorithms for authenticated encryption with associated data (AEAD) that are based on the composition of the Advanced Encryption Standard (AES) in the Cipher Block Chaining (CBC) mode of operation for encryption, and the HMAC-SHA message authentication code (MAC). These are randomized encryption algorithms, and thus are suitable for use with applications that cannot provide distinct nonces to each invocation of the AEAD encrypt operation.</t></abstract>
</front>
<seriesInfo name='Internet-Draft' value='draft-mcgrew-aead-aes-cbc-hmac-sha2-05' />
<format type='TXT'
target='http://www.ietf.org/internet-drafts/draft-mcgrew-aead-aes-cbc-hmac-sha2-05.txt' />
</reference>
<reference anchor='RFC2119'>
<front>
<title abbrev='RFC Key Words'>Key words for use in RFCs to Indicate Requirement Levels</title>
<author initials='S.' surname='Bradner' fullname='Scott Bradner'>
<organization>Harvard University</organization>
<address>
<postal>
<street>1350 Mass. Ave.</street>
<street>Cambridge</street>
<street>MA 02138</street></postal>
<phone>- +1 617 495 3864</phone>
<email>sob@harvard.edu</email></address></author>
<date year='1997' month='March' />
<area>General</area>
<keyword>keyword</keyword>
<abstract>
<t>
In many standards track documents several words are used to signify
the requirements in the specification. These words are often
capitalized. This document defines these words as they should be
interpreted in IETF documents. Authors who follow these guidelines
should incorporate this phrase near the beginning of their document:
<list>
<t>
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.
</t></list></t>
<t>
Note that the force of these words is modified by the requirement
level of the document in which they are used.
</t></abstract></front>
<seriesInfo name='BCP' value='14' />
<seriesInfo name='RFC' value='2119' />
<format type='TXT' octets='4723' target='http://www.rfc-editor.org/rfc/rfc2119.txt' />
<format type='HTML' octets='17970' target='http://xml.resource.org/public/rfc/html/rfc2119.html' />
<format type='XML' octets='5777' target='http://xml.resource.org/public/rfc/xml/rfc2119.xml' />
</reference>
<reference anchor='RFC3394'>
<front>
<title>Advanced Encryption Standard (AES) Key Wrap Algorithm</title>
<author initials='J.' surname='Schaad' fullname='J. Schaad'>
<organization /></author>
<author initials='R.' surname='Housley' fullname='R. Housley'>
<organization /></author>
<date year='2002' month='September' /></front>
<seriesInfo name='RFC' value='3394' />
<format type='TXT' octets='73072' target='http://www.rfc-editor.org/rfc/rfc3394.txt' />
</reference>
<reference anchor='RFC3447'>
<front>
<title>Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1</title>
<author initials='J.' surname='Jonsson' fullname='J. Jonsson'>
<organization /></author>
<author initials='B.' surname='Kaliski' fullname='B. Kaliski'>
<organization /></author>
<date year='2003' month='February' />
<abstract>
<t>This memo represents a republication of PKCS #1 v2.1 from RSA Laboratories' Public-Key Cryptography Standards (PKCS) series, and change control is retained within the PKCS process. The body of this document is taken directly from the PKCS #1 v2.1 document, with certain corrections made during the publication process. This memo provides information for the Internet community.</t></abstract></front>
<seriesInfo name='RFC' value='3447' />
<format type='TXT' octets='143173' target='http://www.rfc-editor.org/rfc/rfc3447.txt' />
</reference>
<reference anchor='RFC3610'>
<front>
<title>Counter with CBC-MAC (CCM)</title>
<author initials='D.' surname='Whiting' fullname='D. Whiting'>
<organization /></author>
<author initials='R.' surname='Housley' fullname='R. Housley'>
<organization /></author>
<author initials='N.' surname='Ferguson' fullname='N. Ferguson'>
<organization /></author>
<date year='2003' month='September' />
<abstract>
<t>Counter with CBC-MAC (CCM) is a generic authenticated encryption block cipher mode. CCM is defined for use with 128-bit block ciphers, such as the Advanced Encryption Standard (AES).</t></abstract></front>
<seriesInfo name='RFC' value='3610' />
<format type='TXT' octets='64509' target='http://www.rfc-editor.org/rfc/rfc3610.txt' />
</reference>
<reference anchor='RFC5752'>
<front>
<title>Multiple Signatures in Cryptographic Message Syntax (CMS)</title>
<author initials='S.' surname='Turner' fullname='S. Turner'>
<organization /></author>
<author initials='J.' surname='Schaad' fullname='J. Schaad'>
<organization /></author>
<date year='2010' month='January' />
<abstract>
<t>Cryptographic Message Syntax (CMS) SignedData includes the SignerInfo structure to convey per-signer information. SignedData supports multiple signers and multiple signature algorithms per signer with multiple SignerInfo structures. If a signer attaches more than one SignerInfo, there are concerns that an attacker could perform a downgrade attack by removing the SignerInfo(s) with the \'strong' algorithm(s). This document defines the multiple-signatures attribute, its generation rules, and its processing rules to allow signers to convey multiple SignerInfo objects while protecting against downgrade attacks. Additionally, this attribute may assist during periods of algorithm migration. [STANDARDS-TRACK]</t></abstract></front>
<seriesInfo name='RFC' value='5752' />
<format type='TXT' octets='34502' target='http://www.rfc-editor.org/rfc/rfc5752.txt' />
</reference>
<reference anchor='RFC5990'>
<front>
<title>Use of the RSA-KEM Key Transport Algorithm in the Cryptographic Message Syntax (CMS)</title>
<author initials='J.' surname='Randall' fullname='J. Randall'>
<organization /></author>
<author initials='B.' surname='Kaliski' fullname='B. Kaliski'>
<organization /></author>
<author initials='J.' surname='Brainard' fullname='J. Brainard'>
<organization /></author>
<author initials='S.' surname='Turner' fullname='S. Turner'>
<organization /></author>
<date year='2010' month='September' />
<abstract>
<t>The RSA-KEM Key Transport Algorithm is a one-pass (store-and-forward) mechanism for transporting keying data to a recipient using the recipient's RSA public key. ("KEM" stands for "key encapsulation mechanism".) This document specifies the conventions for using the RSA-KEM Key Transport Algorithm with the Cryptographic Message Syntax (CMS). The ASN.1 syntax is aligned with an expected forthcoming change to American National Standard (ANS) X9.44.</t></abstract></front>
<seriesInfo name='RFC' value='5990' />
<format type='TXT' octets='52579' target='http://www.rfc-editor.org/rfc/rfc5990.txt' />
</reference>
<reference anchor='RFC5652'>
<front>
<title>Cryptographic Message Syntax (CMS)</title>
<author initials='R.' surname='Housley' fullname='R. Housley'>
<organization /></author>
<date year='2009' month='September' />
<abstract>
<t>This document describes the Cryptographic Message Syntax (CMS). This syntax is used to digitally sign, digest, authenticate, or encrypt arbitrary message content. [STANDARDS-TRACK]</t></abstract></front>
<seriesInfo name='STD' value='70' />
<seriesInfo name='RFC' value='5652' />
<format type='TXT' octets='126813' target='http://www.rfc-editor.org/rfc/rfc5652.txt' />
</reference>
<reference anchor='RFC7159'>
<front>
<title>The JavaScript Object Notation (JSON) Data Interchange Format</title>
<author initials='T.' surname='Bray' fullname='T. Bray'>
<organization /></author>
<date year='2014' month='March' />
<abstract>
<t>JavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. It was derived from the ECMAScript Programming Language Standard. JSON defines a small set of formatting rules for the portable representation of structured data.</t><t> This document removes inconsistencies with other specifications of JSON, repairs specification errors, and offers experience-based interoperability guidance.</t></abstract></front>
<seriesInfo name='RFC' value='7159' />
<format type='TXT' octets='27451' target='http://www.rfc-editor.org/rfc/rfc7159.txt' />
</reference>
<reference anchor="AES-GCM" >
<front>
<title>NIST Special Publication 800-38D: Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC.</title>
<author initials="M." surname="Dworkin">
<organization>U.S. National Institute of Standards and Technology</organization>
</author>
<date year="2015" month="April"/>
</front>
</reference>
</references>
<section anchor="AE-algo" title="AEAD and AE algorithms">
<t>The set of encryption algorithms that can be used with this
specification is restricted to authenticated encryption (AE) and
authenticated encryption with additional data (AEAD) algorithms.
This means that there is a strong check that the data decrypted by the
recipient is the same as what was encrypted by the sender.
Encryption modes such as counter have no check on this at all.
The CBC encryption mode had a weak check that the data is correct,
given a random key and random data, the CBC padding check will pass
one out of 256 times.
There have been several times that a normal encryption mode has been
combined with an integrity check to provide a content encryption mode
that does provide the necessary authentication.
AES-GCM <xref target="AES-GCM"/>, AES-CCM <xref target="RFC3610"/>, AES-CBC-HMAC
<xref target="I-D.mcgrew-aead-aes-cbc-hmac-sha2"/> are examples of these composite
modes.</t>
<t>PKCS v1.5 RSA key transport does not qualify as an AE algorithm.
There are only three bytes in the encoding that can be checked as
having decrypted correctly, the rest of the content can only be
probabilistically checked as having decrypted correctly.
For this reason, PKCS v1.5 RSA key transport MUST NOT be used with
this specification.
RSA-OAEP was designed to have the necessary checks that that content
correctly decrypted and does qualify as an AE algorithm.</t>
<t>When dealing with authenticated encryption algorithms, there is always
some type of value that needs to be checked to see if the
authentication level has passed.
This authentication value may be:</t>
<t><list style="symbols">
<t>A separately generated tag computed by both the encrypter and
decrypter and then compared by the decryptor.
This tag value may be either placed at the end of the cipher text
(the decision we made) or kept separately (the decision made by the
JOSE working group).
This is the approach followed by AES-GCM <xref target="AES-GCM"/> and AES-CCM <xref target="RFC3610"/>.</t>
<t>A fixed value which is part of the encoded plain text.
This is the approach followed by the AES key wrap algorithm <xref target="RFC3394"/>.</t>
<t>A computed value is included as part of the encoded plain text.
The computed value is then checked by the decryptor using the same computation path.
This is the approach followed by RSAES-OAEP <xref target="RFC3447"/>.</t>
</list></t>
</section>
<section anchor="three-levels-of-recipient-information" title="Three Levels of Recipient Information">
<t>All of the currently defined Key Management methods only use two levels of the COSE_Encrypt structure.
The first level is the message content and the second level is the content key encryption.
However, if one uses a key management technique such as RSA-KEM (see Appendix A of RSA-KEM <xref target="RFC5990"/>, then
it make sense to have three levels of the COSE_Encrypt structure.</t>
<t>These levels would be:</t>
<t><list style="symbols">
<t>Level 0: The content encryption level. This level contains the payload of the message.</t>
<t>Level 1: The encryption of the CEK by a KEK.</t>
<t>Level 2: The encryption of a long random secret using an RSA key and a key derivation function to convert that secret into the KEK.</t>
</list></t>
</section>
<section anchor="examples" title="Examples">
<t>The examples can be found at https://github.com/cose-wg/Examples. I am currently still in the process of getting the examples up there along with some control information for people to be albe to check and reproduce the examples.</t>
<section anchor="direct-mac" title="Direct MAC">
<t>This example has some features that are in questions but not yet incorporated in the document.</t>
<t>To make it easier to read, this uses CBOR’s diagnostic notation rather than a binary dump.</t>
<t>This example is uses HMAC with SHA-256 as the digest algorithm. The key manangment is uses two static ECDH keys along with HKDF to directly derive the key used in the HMAC operation.</t>
<figure><artwork type="CBORdiag"><![CDATA[
[
3,
h'a163616c67654853323536',
null,
h'596f752063616e20747275737420757320746f20737469636b20776974682079
6f75207468726f75676820746869636b20616e64207468696e3f746f20746865
2062697474657220656e642e20416e6420796f752063616e2074727573742075
7320746f206b65657020616e7920736563726574206f6620796f7572733f636c
6f736572207468616e20796f75206b65657020697420796f757273656c662e20
42757420796f752063616e6e6f7420747275737420757320746f206c65742079
6f7520666163652074726f75626c6520616c6f6e652c20616e6420676f206f66
6620776974686f7574206120776f72642e2057652061726520796f7572206672
69656e64732c2046726f646f2e',
h'18adb1630f27643924f584e319b284463ef44116b5f863a5c048a546e26c804a',
null,
{"alg": "ECDH-SS",
"kid": "meriadoc.brandybuck@buckland.example",
"spk": {"kid": "peregrin.took@tuckborough.example"},
"apu": h'4d8553e7e74f3c6a3a9dd3ef286a8195cbf8a23d19558ccfec7d34b8
24f42d92bd06bd2c7f0271f0214e141fb779ae2856abf585a58368b017e7f2a
9e5ce4db5'},
null,
null,
null
]
]]></artwork></figure>
</section>
<section anchor="wrapped-mac" title="Wrapped MAC">
<t>This example has some features that are in questions but not yet incorporated in the document.</t>
<t>To make it easier to read, this uses CBOR’s diagnostic notation rather than a binary dump.</t>
<t>This exmple uses AES-128-MAC trucated to 64-bits as the digest algorithm. It uses AES-256 Key wrap for the key manangment algorithm wrapping the 128-bit key used for the digest algorthm.</t>
<figure><artwork type="CBORdiag"><![CDATA[
[3, h'a163616c676e4145532d3132382d4d41432d3634', null, h'596f75206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', h'474102be6c96d590', [[null, {"alg": "A256KW", "kid":
"018c0ae5-4d9b-471b-bfd6-eef314bc7037"}, null, h'711ab0dc2fc4585dc
e27effa6781c8093eba906f227b6eb0', null]]]
]]></artwork></figure>
</section>
<section anchor="multi-recipient-mac-message" title="Multi-recipient MAC message">
<t>This example has some features that are in questions but not yet incorporated in the document.</t>
<t>To make it easier to read, this uses CBOR’s diagnostic notation rather than a binary dump.</t>
<t>This example uses HMAC with SHA-256 for the digest algorithm. There are three different key manangment techniques applied:</t>
<t><list style="symbols">
<t>An ephemeral static ECDH key agrement operation using AES-128 key wrap on the digest key.</t>
<t>Key transport using RSA-OAEP with SHA-256 for the hash and the mfg function operations.</t>
<t>AES 256-bit Key wrap using a pre-shared secret.</t>
</list></t>
<figure><artwork type="CBORdiag"><![CDATA[
[3, h'a163616c67654853323536', null, h'596f752063616e2074727573742
0757320746f20737469636b207769746820796f75207468726f756768207468696
36b20616e64207468696e3f746f207468652062697474657220656e642e20416e6
420796f752063616e20747275737420757320746f206b65657020616e792073656
3726574206f6620796f7572733f636c6f736572207468616e20796f75206b65657
020697420796f757273656c662e2042757420796f752063616e6e6f74207472757
37420757320746f206c657420796f7520666163652074726f75626c6520616c6f6
e652c20616e6420676f206f666620776974686f7574206120776f72642e2057652
061726520796f757220667269656e64732c2046726f646f2e', h'87072b78b740
be1bd34176983fea202f031675753d74978c5eb6050169766d3b', [[null,
{"alg": "ECDH-ES+A128KW", "kid": "bilbo.baggins@hobbiton.example",
"epk": {"kty": "EC", "crv": "P-521", "x": h'01b77bff3e35f9c9c3b7f
5263911655303dd9a45d5fc6b6c629a8fb34715c73bca4f61dcf25ea57df50ad07
269130298f8fc3476d6c077943ad08214bc0bae80b3bc', "y": h'1b366dcc649
00a6d24fbe9a1d844baf0cfc7e0ffa11cac3ebb4dea7839fa41e244cbc148fa5de
51ecec2d03a76f035e0f0f3d679d26fa6221552efef37e6ea7548'}}, null,
h'3b256a47bb9a9b84616da0165f35eec4f264a4e06dff39a899802fb0665231c2
0f6b0d7b8fc70952', null], [null, {"alg": "RSA-OAEP-256", "kid":
"bilbo.baggins@hobbiton.example"}, null, h'6b9814171c92c594ab345b4
9023e0ce9628f374f657d3fc6745ccb0fd6a367471a8ab7766e8aace7adb0f59f5
e750f9c7c0deaa503061e46836b04ae69f8aa26cc63ef978cc03a505acccc0b9e0
cc52f9eb82b4590aa2aa33d86da3152a6a2c3b01b33afa471298471f3018bbcd8a
b5aa7b778cc96bc85b65752e71c06ac553661e01fd786413ba26d5d0f4a4406669
b55db6e08af61dd92a287d0e2cd1497b28e4691ab64de9925ae7d41c7ea3015b0c
a3e16d98caeac6828f58a696d3a767682100d13b7c6168ac94e9505eb54b77c598
5dc86edacfd61e063b2aa6b23e24e390c83614cce27e054f0220ee4c6cd5696e2a
237d0d86700d3d7d718b4ff6b9b', null], [null, {"alg": "A256KW",
"kid": "018c0ae5-4d9b-471b-bfd6-eef314bc7037"}, null, h'02a8d3017e
57088df19104fa492ede156e6a24f7b2b11eeed0fffefcf8f3f2fcadbfbec97267
7027', null]]]
]]></artwork></figure>
</section>
<section anchor="direct-ecdh" title="Direct ECDH">
<t>This example has some features that are in questions but not yet incorporated in the document.</t>
<t>To make it easier to read, this uses CBOR’s diagnostic notation rather than a binary dump.</t>
<t>Encoded in CBOR - 216 bytes, content is 14 bytes long</t>
<figure><artwork type="CBORdiag"><![CDATA[
[
2,
null,
{"alg": "A128GCM"},
h'656d6a73ccf1b35fb99044e1',
h'd7b27b67a81b212ee513b148454fe2d571d51bb679239769f5d2299bb96b',
null,
{
"alg": "ECDH-ES",
"epk": {
"kty": "EC",
"crv": "P-256",
"x": h'00b81ff1de0eeba27613027526d83b5f4cbffaca433488e3805
e7a75c43bd1b966',
"y": h'00d142a334ac8790dc821abe9362434daeb00c1b8b076843e51
a4a4717b30c54ce'},
"kid": "meriadoc.brandybuck@buckland.example"
},
null,
null,
null
]
]]></artwork></figure>
</section>
<section anchor="single-signature" title="Single Signature">
<t>This example has some features that are in questions but not yet cooperated in the document.</t>
<t>To make it easier to read, this uses CBOR’s diagnostic notation rather than a binary dump.</t>
<figure><artwork type="CBORdiag"><![CDATA[
[
1,
null,
null,
h'436f6e74656e7420537472696e67',
null,
{
"kid": "bilbo.baggins@hobbiton.example",
"alg": "PS256"
},
h'5afe80ec9f208b4719a3bd688c803a3154b1ff25af86e054173ad6ddf71
ba77a4a2b793beed077a4e1a8a69ac1277c457f636691cb4a7d3dc67b47
ec84c067076b720236bae498bdb21deebbc0a0f525f9a24b336d51e2b3e
ffd67df3e051405a3599aed83b8a8e94e4194dded2f661e5e6894825779
b79b463bd4f477f33356cf8aecfa8a543344d2620145be8a72a712f9854
57040140176164c77cdae7cc480ae4357683cce79b97ddb10f390862a24
2aae1aa391cc730b1631f020874a8a6efc77b08f027323e2c4ae85eeb3e
5dc715e0e2fa8aec63fb828d7a2c45e361e249117bd8b41e1e12388412d
8ce3809c9a2172afda5ca7c5839896825da66a50'
]
]]></artwork></figure>
</section>
<section anchor="multiple-signers" title="Multiple Signers">
<t>This example has some features that are in questions but not yet cooperated in the document.</t>
<t>To make it easier to read, this uses CBOR’s diagnostic notation rather than a binary dump.</t>
<t>Encoded in CBOR - 491 bytes, content is 14 bytes long</t>
<figure><artwork type="CBORdiag"><![CDATA[
[
1,
null,
null,
h'436f6e74656e7420537472696e67',
[
[
null,
{
"kid": "bilbo.baggins@hobbiton.example",
"alg": "PS256"
},
h'5afe80ec9f208b4719a3bd688c803a3154b1ff25af86e054173ad6d
df71ba77a4a2b793beed077a4e1a8a69ac1277c457f636691cb4a7d
3dc67b47ec84c067076b720236bae498bdb21deebbc0a0f525f9a24
b336d51e2b3effd67df3e051405a3599aed83b8a8e94e4194dded2f
661e5e6894825779b79b463bd4f477f33356cf8aecfa8a543344d26
20145be8a72a712f985457040140176164c77cdae7cc480ae435768
3cce79b97ddb10f390862a242aae1aa391cc730b1631f020874a8a6
efc77b08f027323e2c4ae85eeb3e5dc715e0e2fa8aec63fb828d7a2
c45e361e249117bd8b41e1e12388412d8ce3809c9a2172afda5ca7c
5839896825da66a50'
],
[
null,
{
"kid": "bilbo.baggins@hobbiton.example",
"alg": "ES512"
},
h'00e9769c05afb2d93baf5a0c2cace1747b5091f50596831911c67ebf
76f4220adb53698fe7831000d526887893d67de05ead1bbe378ce9e9
731bda4cd37f53dcf8d40186c46d872795b566682c113cc9d5bf5a8c
5321fd50a003237115decf0cb8b09e5c3cb50bc2203af45bebd51e6c
4d0ec51170d5b9ac1b21a2017a50d7c15b6de8f9'
]
]
]
]]></artwork></figure>
</section>
</section>
<section anchor="processing-parameter-table" title="Processing Parameter Table">
<t>This table contains a list of all of the parameters for use in signature and encryption message types defined by the JOSE document set. In the table is the data value type to be used for CBOR as well as the integer value that can be used as a replacement for the name in order to further decrease the size of the sent item.</t>
<texttable>
<ttcol align='left'>name</ttcol>
<ttcol align='left'>number</ttcol>
<ttcol align='left'>CBOR type</ttcol>
<ttcol align='left'>comments</ttcol>
<c>alg</c>
<c>*</c>
<c>tstr</c>
<c>presence is required</c>
<c>apu</c>
<c>*</c>
<c>bstr</c>
<c> </c>
<c>apv</c>
<c>*</c>
<c>bstr</c>
<c> </c>
<c>crit</c>
<c>*</c>
<c>tstr*</c>
<c> </c>
<c>cty</c>
<c>*</c>
<c>tstr</c>
<c> </c>
<c>enc</c>
<c>*</c>
<c> </c>
<c>use alg instead</c>
<c>epk</c>
<c>*</c>
<c>map</c>
<c>contains a COSE key not a JWK key</c>
<c>iv</c>
<c>*</c>
<c> </c>
<c>use field in array instead</c>
<c>jku</c>
<c>*</c>
<c>tstr</c>
<c> </c>
<c>jwk</c>
<c>*</c>
<c>map</c>
<c>contains a COSE key not a JWK key</c>
<c>kid</c>
<c>*</c>
<c>tstr</c>
<c> </c>
<c>p2c</c>
<c>*</c>
<c>int</c>
<c> </c>
<c>p2s</c>
<c>*</c>
<c>bstr</c>
<c> </c>
<c>tag</c>
<c>*</c>
<c> </c>
<c>tag is included in the cipher text</c>
<c>typ</c>
<c>*</c>
<c> </c>
<c>use cty for the content type, no concept of a different wrapper type</c>
<c>x5c</c>
<c>*</c>
<c>bstr*</c>
<c> </c>
<c>x5t</c>
<c>*</c>
<c>bstr</c>
<c> </c>
<c>x5t#S256</c>
<c>*</c>
<c>bstr</c>
<c> </c>
<c>x5u</c>
<c>*</c>
<c>tstr</c>
<c> </c>
<c>zip</c>
<c>*</c>
<c>tstr</c>
<c>only used at content level</c>
</texttable>
</section>
<section anchor="key-parameter-tables" title="Key Parameter Tables">
<t>This table contains a list of all of the parameters defined for keys that were defined by the JOSE document set. In the table is the data value type to be used for CBOR as well as the integer value that can be used as a replacement for the name in order to further decrease the size of the sent item.</t>
<texttable>
<ttcol align='left'>name</ttcol>
<ttcol align='left'>number</ttcol>
<ttcol align='left'>CBOR type</ttcol>
<c>kty</c>
<c>*</c>
<c>tstr</c>
<c>use</c>
<c>*</c>
<c>tstr</c>
<c>key_ops</c>
<c>*</c>
<c>tstr*</c>
<c>alg</c>
<c>*</c>
<c>tstr</c>
<c>kid</c>
<c>*</c>
<c>tstr</c>
<c>x5u</c>
<c>*</c>
<c>tstr</c>
<c>x5c</c>
<c>*</c>
<c>bstr*</c>
<c>x5t</c>
<c>*</c>
<c>bstr</c>
<c>xt5#S256</c>
<c>*</c>
<c>bstr</c>
</texttable>
<t>This table contains a list of all of the parameters that were defined by the JOSE document set for a specific key type. In the table is the data value type to be used for CBOR as well as the integer value that can be used as a replacement for the name in order to further decrease the size of the sent item.
Parameters dealing with keys</t>
<texttable>
<ttcol align='left'>key type</ttcol>
<ttcol align='left'>name</ttcol>
<ttcol align='left'>number</ttcol>
<ttcol align='left'>CBOR type</ttcol>
<c>EC</c>
<c>d</c>
<c>*</c>
<c>bstr</c>
<c>EC</c>
<c>x</c>
<c>*</c>
<c>bstr</c>
<c>EC</c>
<c>y</c>
<c>*</c>
<c>bstr</c>
<c>RSA</c>
<c>e</c>
<c>*</c>
<c>bstr</c>
<c>RSA</c>
<c>n</c>
<c>*</c>
<c>bstr</c>
<c>RSA</c>
<c>d</c>
<c>*</c>
<c>bstr</c>
<c>RSA</c>
<c>p</c>
<c>*</c>
<c>bstr</c>
<c>RSA</c>
<c>q</c>
<c>*</c>
<c>bstr</c>
<c>RSA</c>
<c>dp</c>
<c>*</c>
<c>bstr</c>
<c>RSA</c>
<c>dq</c>
<c>*</c>
<c>bstr</c>
<c>RSA</c>
<c>qi</c>
<c>*</c>
<c>bstr</c>
<c>RSA</c>
<c>oth</c>
<c>*</c>
<c>bstr</c>
<c>RSA</c>
<c>r</c>
<c>*</c>
<c>bstr</c>
<c>RSA</c>
<c>t</c>
<c>*</c>
<c>bstr</c>
<c>oct</c>
<c>k</c>
<c>*</c>
<c>bstr</c>
</texttable>
</section>
</back>
</rfc>
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