| Network Working Group | J. Schaad |
| Internet-Draft | August Cellars |
| Intended status: Informational | June 10, 2015 |
| Expires: December 12, 2015 |
CBOR Encoded Message Syntax
draft-schaad-cose-msg-00
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.
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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 [RFC7159]. This document does the same work for use with the Concise Binary Object Representation (CBOR) [RFC7049] document format. While there is a strong attempt to keep the flavor of the original JOSE documents, two considerations are taking into account:
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 [RFC2119].
When the words appear in lower case, their natural language meaning is used.
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) [I-D.greevenbosch-appsawg-cbor-cddl].
The COSE_MSG structure is a top level CBOR object which corresponds to the DataContent type in [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.
COSE_MSG = {msg_type=>1, COSE_Sign} /
{msg_type=>2, COSE_encrypt} /
{msg_type=>3, COSE_mac}
COSE_Tagged_MSG = #6.999(COSE_MSG) ; Replace 999 with TBD1
The top level of each of the COSE message structures are encoded as arrays.
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.
Implementations SHOULD be prepared to find an integer in the location which does not correspond to the values 1 to 3. 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.
The structure of COSE has been designed to have two buckets of information that are not considered to be part of the message structure itself, but are used for holding information about algorithms, keys, or evaluation hints for the processing of the layer. These two buckets are available for use in all of the structures in this document except for keys. While these buckets can be present, they may not all be usable in all instances. For example, while the protected bucket is present for recipient structures, most of the algorithms that are-used for recipients do not provide the necessary functionality to provide the needed protection and thus the element is not used.
Both buckets are implemented as CBOR maps. The maps can be keyed by negative integers, unsigned integers and strings. The negative and unsigned integers are used for compactness of encoding. The value portion is dependent on the key definition. Both maps use the same set of key/value pairs. The integer key range has been divided into several sections with a standard range, a private range, and a range that is dependent on the algorithm selected. The tables of keys defined can be found in Appendix E.
Two buckets are provided for each layer:
Both of the buckets are optional and are omitted if there are no items contained in the map. The CDDL fragment which describes the two buckets is:
keys = int / tstr
header_map = {+ keys => any }
Headers = (
? protected => bstr,
? unprotected => header_map
)
TODO: Do we need to repeat definitions for all or just for some and refer to the JOSE documents?
TODO: Should we move table Appendix E to here or leave it as an appendix. Some what redundant if we document things in text.
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.
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 [RFC5652].) More detailed information on multiple signature evaluation can be found in [RFC5752].
The CDDL grammar structure for a signature message is:
COSE_Sign = (
Headers,
? payload => bstr,
signatures=> [+{COSE_signature}]
)
The keys in the COSE_Sign map are keyed by the values in Appendix D. While other keys can be present in the map, it is not generally a recommended practice. The other keys can be either of integer or string type, use of other types is strongly discouraged. See the note in {{CBOR-Canonical} about options for allowing or disallowing other keys.
The fields is the structure have the following semantics:
The keys in the COSE_signature map are keyed by the values in Appendix D. While other keys can be present in the map, it is not generally a recommended practice. The other keys can be either of integer or string type, use of other types is strongly discouraged. See the note in {{CBOR-Canonical} about options for allowing or disallowing other keys.
The CDDL grammar structure for a signature is:
COSE_signature = (
? protected => bstr,
? unprotected => header_map,
signature => bstr
)
The fields in the structure have the following semantics:
The COSE structure used to create the byte stream to be signed uses the following CDDL grammar structure:
Sig_structure = [
body_protected => bstr,
sign_protected => bstr,
payload => bstr
]
How to compute a signature:
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 [RFC5652] and [RFC7516] where different structures are used for the plain text and for the different key management techniques.
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 Appendix A for more details about the different types of algorithms.
I don’t follow/understand this text{:aeds}
The CDDL grammar structure for encryption is:
COSE_encrypt = (
Headers,
? iv => bstr,
? aad => bstr,
? ciphertext => bstr,
? recipients => [+COSE_encrypt_a]
)
COSE_encrypt_a = {COSE_encrypt}
Description of the fields:
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.
The names of the key management methods used here are the same as are defined in [RFC7517]. Other specifications use different terms for the key management methods or do not support some of the key management methods.
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 [RFC7518] were extended to allow for authenticated data. In that event the use of the ‘protected’ field, which is current forbidden below, would be permitted.
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.
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.
The COSE_encrypt structure for the recipient is organized as follows:
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.
The COSE_encrypt structure for the recipient is organized as follows:
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.
The COSE_encrypt structure for the recipient is organized as follows:
Direct Key Agreement derives the CEK from the shared secret computed by the key agreement operation.
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.
The COSE_encrypt structure for the recipient is organized as follows:
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.
The COSE_encrypt structure for the recipient is organized as follows:
The encryption algorithm for AEAD algorithms is fairly simple.
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.
Enc_structure = [ protected => bstr, aad => bstr ]
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.
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.)
COSE_mac = ( Headers, ? payload => bstr, tag => bstr, ? recipients => [+COSE_encrypt_a] )
Field descriptions:
MAC_structure = [ protected => bstr, payload => bstr ]
How to compute a MAC:
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.
For COSE we use the same set of fields that were defined in [RFC7517].
COSE_Key = {
kty => tstr / int,
? key_ops => [+tstr / int ],
? alg => tstr / int,
? kid => bstr,
* keys => values
}
COSE_KeySet = [+COSE_Key]
The element “kty” is a required element in a COSE_Key map.
All other elements are optional and not all of the elements listed in [RFC7517] or [RFC7518] have been listed here even though they can all appear in a COSE_Key map.
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.
The same fields defined in [RFC7517] are used here with the following changes in rules:
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:
While it is permitted to have key values other than those specified in this document in the outer maps (COSE_Sign, COSE_Signature, COSE_encrypt, COSE_recipient and COSE_mac), doing so is not encouraged. Applications should make a determination if it will be permitted for that application. In general, any needed new fields can be accomadated by the introduction of new header fields to be carried in the protected or unprotected fields. Applications that need to have new fields in these maps should consider getting new message types assigned for these usages. Without this change, old applications will not see and process the new fields.
It is requested that IANA assign a new tag from the “Concise Binary Object Represetion (CBOR) Tags” registry. It is requested that the tag be assigned in the 0 to 23 value range.
Tag Value: TBD1
Data Item: CBOR map
Semantics: COSE security message.
It is requested that IANA create a new registry entitled “COSE Header Key”.
The initial contents of the registry can be found in Appendix E. The specification column for all rows in that table should be this document.
NOTE: Need to review the range assignments. It does not necessarily make sense as specification required uses 1 byte positive integers and 2 byte strings.
It is requested that IANA create a new registry entitled “COSE Header Algorithm Keys”.
The initial contents of the registry can be found in Appendix F. The specification column for all rows in that table should be this document.
It is requested that IANA create a new registry entitled “COSE Algorithm Registry”.
The initial contents of the registry can be found in Appendix G. The specification column for all rows in that table should be this document.
It is requested that IANA create a new registry entitied “COSE Key Map Registry”.
The columns of the registry are:
This registry will be initially populated bythe values in Appendix I. The specification column for all of these entries will be this document.
It is requested that IANA create a new registry “COSE Key Parameters”.
The columns of the table are:
This registry will be initially populated bythe values in Appendix J. The specification column for all of these entries will be this document.
There are security considerations:
| [I-D.greevenbosch-appsawg-cbor-cddl] | Vigano, C., Birkholz, H. and R. Sun, "CBOR data definition language: a notational convention to express CBOR data structures.", Internet-Draft draft-greevenbosch-appsawg-cbor-cddl-05, March 2015. |
| [RFC7049] | Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", RFC 7049, October 2013. |
| [RFC7518] | Jones, M., "JSON Web Algorithms (JWA)", RFC 7518, May 2015. |
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 [AES-GCM], AES-CCM [RFC3610], AES-CBC-HMAC [I-D.mcgrew-aead-aes-cbc-hmac-sha2] are examples of these composite modes.
2PKCS 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.
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:
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 [RFC5990], then it make sense to have three levels of the COSE_Encrypt structure.
These levels would be:
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.
This example has some features that are in questions but not yet incorporated in the document.
To make it easier to read, this uses CBOR’s diagnostic notation rather than a binary dump.
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.
{1: 3, 2: h'A10104', 4: h'546869732069732074686520636F6E74656E742E',
10: h'82C136D2C8CB27356635FAFE6F2E1AB2BC23FA706A33357DB017EE51710EEDE5',
9: [
{3: {1: "ECDH-SS", 5: "meriadoc.brandybuck@buckland.example",
"spk": {"kid": "peregrin.took@tuckborough.example"},
"apu": h'4D8553E7E74F3C6A3A9DD3EF286A8195CBF8A23D19558CCFEC7D34
B824F42D92BD06BD2C7F0271F0214E141FB779AE2856ABF585A58368B017E7F2A
9E5CE4DB5'}}]}
This example has some features that are in questions but not yet incorporated in the document.
To make it easier to read, this uses CBOR’s diagnostic notation rather than a binary dump.
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.
{1: 3, 2: h'A1016E4145532D3132382D4D41432D3634',
4: h'546869732069732074686520636F6E74656E742E',
10: h'A61AE6CFB7CABCC9', 9: [
{3: {1: -5, 5: "018c0ae5-4d9b-471b-bfd6-eef314bc7037"},
4: h'711AB0DC2FC4585DCE27EFFA6781C8093EBA906F227B6EB0'}]}
This example has some features that are in questions but not yet incorporated in the document.
To make it easier to read, this uses CBOR’s diagnostic notation rather than a binary dump.
This example uses HMAC with SHA-256 for the digest algorithm. There are three different key manangment techniques applied:
{1: 3, 2: h'A10104', 4: h'546869732069732074686520636F6E74656E742E',
10: h'051FA3288A39AC726B4FAE79A4B93FB17D8DC3F6E666247EE7AD40CE1665FCDE',
9: [
{3: {1: "ECDH-ES+A128KW",
5: h'62696C626F2E62616767696E7340686F626269746F6E2E6578616D706C65',
4: {1: 1, -1: 5, -2: h'43B12669ACAC3FD27898FFBA0BCD2E6C366D53BC4DB
71F909A759304ACFB5E18CDC7BA0B13FF8C7636271A6924B1AC63C02688075
B55EF2D613574E7DC242F79C3',
-3: h'812DD694F4EF32B11014D74010A954689C6B6E8785B333D1AB44F22B
9D1091AE8FC8AE40B687E5CFBE7EE6F8B47918A07BB04E9F5B1A51A334A16B
C09777434113'}},
4: h'1B120C848C7F2F8943E402CBDBDB58EFB281753AF4169C70D0126C0D164362771
60821790EF4FE3F'},
{3: {1: -2, 5: h'62696C626F2E62616767696E7340686F626269746F6E2E6578616D
706C65'},
4: h'46C4F88069B650909A891E84013614CD58A3668F88FA18F3852940A20B3509859
1D3AACF91C125A2595CDA7BEE75A490579F0E2F20FD6BC956623BFDE3029C318
F82C426DAC3463B261C981AB18B72FE9409412E5C7F2D8F2B5ABAF780DF6A282D
B033B3A863FA957408B81741878F466DCC437006CA21407181A016CA608CA8208
BD3C5A1DDC828531E30B89A67EC6BB97B0C3C3C92036C0CB84AA0F0CE8C3E4A21
5D173BFA668F116CA9F1177505AFB7629A9B0B5E096E81D37900E06F561A32B6B
C993FC6D0CB5D4BB81B74E6FFB0958DAC7227C2EB8856303D989F93B4A0518307
06A4C44E8314EC846022EAB727E16ADA628F12EE7978855550249CCB58'},
{3: {1: -5, 5: "018c0ae5-4d9b-471b-bfd6-eef314bc7037"},
4: h'0B2C7CFCE04E98276342D6476A7723C090DFDD15F9A518E7736549E99837
0695E6D6A83B4AE507BB'}]}
This example has some features that are in questions but not yet incorporated in the document.
To make it easier to read, this uses CBOR’s diagnostic notation rather than a binary dump.
Encoded in CBOR - 216 bytes, content is 14 bytes long
{1: 2, 2: h'A10101', 7: h'C9CF4DF2FE6C632BF7886413',
4: h'45FCE2814311024D3A479E7D3EED063850F3F0B94EE043BAFDFA14636E632CF6
75AF2DAE',
9: [{3: {1: "ECDH-ES", 5: "meriadoc.brandybuck@buckland.example",
4: {1: 1, -1: 4, -2: h'98F50A4FF6C05861C8860D13A638EA56C3F5AD75
90BBFBF054E1C7B4D91D6280',
-3: h'F01400B089867804B8E9FC96C3932161F1934F4223069170D924B7
E03BF822BB'}}}]}
This example has some features that are in questions but not yet cooperated in the document.
To make it easier to read, this uses CBOR’s diagnostic notation rather than a binary dump.
{1: 1, 4: h'546869732069732074686520636F6E74656E742E',
5: [{2: h'A20165505333383405781E62696C626F2E62616767696E7340686F626
269746F6E2E6578616D706C65',
6: h'4D645B5FF17BCDAD7EB29ABA0EBBFFA747E72767714F26EDBC5B4C1D2
1CBE799B71388CCC73BDB25C4443D0EA2226B774A5B4815ABA82233B33DA
4C3958D08285384A854A8F7F8FA9635A1A63BAB2A5D8CF45939A7FA2D95C
C827EF94EF85276611B957B402BD1756D952597751C7AF5D26023012D3DC
BFD785F9C0BE57F60719EFB0D2F9280A8D2B18D142F76942D007B4E24087
DA4BE8F793B646D7B03A86C12731A8EDB36A95DFE6C281B58388380354A2
94CC21DBC1C1EEE2DB35293AD406F50283874475B9A7E22920BD79B3D055
214EE1C9D941F125548B9F23A87DCC26CBBEFD0919CF6F89E192A78130AC
018D1921EF5B4D0A47659E9CBC1CE58ED26'}]}
This example has some features that are in questions but not yet cooperated in the document.
To make it easier to read, this uses CBOR’s diagnostic notation rather than a binary dump.
Encoded in CBOR - 491 bytes, content is 14 bytes long
{1: 1, 4: h'546869732069732074686520636F6E74656E742E',
5: [{2: h'A10129', 3: {5: "bilbo.baggins@hobbiton.example"},
6: h'1FD44A2BA1A8A0A664024E7E2AFD1D1D1159460E3C03B9BE8C8F60639CE
614F59AF33108B65BBDEF3C330FB97E335DA11EEA9B6CBD7E7908FB8B5F61D
FEB76EC6ED6A62BD9F3D338E373E1903CE2D5D3BD20086BBCA82A6F424E9F4
1591BD6261835A74F0C0425E88666D530B72ADC1E33C10DC1D0361922B6ADC
685B76E5CEA79FACA7C4CB66B1379B3F852A5ACE79A5812C6EE1CD3CC7CC88
F2C9D30FF89D3BD0DE2D0C9355E9712B1BA8AB2F2B065BE0A0D93BFFA27DA0
2221865A2B16093D92F71F9864D92C87057AE591334DB4CF881ECBEC2AC727
77D9C88871C10733D65566B35FBFA6BAB54078C1C73AE8758196221FB2814E
C283A95D191FB80D616'},
{3: {1: -9, 5: "bilbo.baggins@hobbiton.example"},
6: h'32247A4FD1CA2B69EEEB48CE65D07F2089D79271BB94847F8628DADB7AF
FC1A34C24D10DB3C5E0D00BD9CB3BFB9666BAD6E9752564D35C5CCE375B
A44E2FF33336008D8E07484041DBEFB179EBFFA5455E05D6B24E22DAECF
0D76AD041A13A9DD7E3DAED7F6B09F1831092FFC5CB8BFE7DBF5E047858
02A4CB741395F81E76A3A8AD61'}]}
This table contains the list of all key values that can ocur in the COSE_Sign, COSE_signature, COSE_Encrypt, and COSE_MAC structures.
| name | number | comments |
|---|---|---|
| msg_type | 1 | Occurs only in top level messages |
| protected | 2 | Occurs in all structures |
| unprotected | 3 | Occurs in all structures |
| payload | 4 | Contains the content of the structure |
| signatures | 5 | For COSE_Sign - array of signatures |
| signature | 6 | For COSE_signature only |
| iv | 7 | For COSE_encrypt only |
| aad | 8 | For COSE_encrypt only |
| ciphertext | 4 | TODO: Should we re-use the same as payload or not? |
| recipients | 9 | For COSE_encrypt and COSE_mac |
| tag | 10 | For COSE_mac only |
; message_keys msg_type=1 protected=2 unprotected=3 payload=4 signatures=5 signature=6 iv=7 aad=8 ciphertext=4 recipients=9 tag=10
M00TODO: 1. There is no equivalent to this table in JOSE so we need to get a name for the table and registration rules. 2. Initial registration rules: Number may be a positive or a negative value. Values in the range of -24 to 24 are Standards action required. Values in the range of -256 to -25 and 25 to 255 are specification required with expert review. Values from 256 to 512 are designated for private use. All other values are reserved.
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.
| name | key | value | registry | description |
|---|---|---|---|---|
| alg | 1 | int / tstr | COSE Algorithm Registry | Integers are taken from table Appendix G |
| crit | 2 | [+ (tstr/int)] | COSE Header Key Registry | integer values are from this table. |
| cty | 3 | tstr / int | Value is either a mime-content type or an integer from the mime-content type table | |
| epk | 4 | COSE_Key | contains a COSE key not a JWK key | |
| jku | * | tstr | URL to COSE key object | |
| jwk | * | COSE_Key | contains a COSE key not a JWK key | |
| kid | * | bstr | key identifier | |
| x5c | * | bstr* | X.509 Certificate Chain | |
| x5t | * | bstr | SHA-1 thumbprint of key | |
| x5t#S256 | * | bstr | SHA-256 thumbprint of key | |
| x5u | * | tstr | URL for X.509 certificate | |
| zip | * | int / tstr | Integers are taken from the table Appendix G |
| name | algorithm | key | CBOR type | description |
|---|---|---|---|---|
| apu | ECDH | -1 | bstr | |
| apv | ECDH | -2 | bstr | |
| iv | A128GCMKW, A192GCMKW, A256GCMKW | -1 | bstr | |
| iv | A128GCM, A192GCM, A256GCM | -1 | bstr | |
| p2c | PBE | -1 | int | |
| p2s | PBE | -2 | bstr |
This table contains all of the defined algorithms for COSE.
| name | key | description |
|---|---|---|
| HS256 | 4 | HMAC w/ SHA-256 |
| HS384 | 5 | HMAC w/ SHA-384 |
| HS512 | 6 | HMAC w/ SHA-512 |
| RS256 | * | RSASSA-v1.5 w/ SHA-256 |
| RS384 | * | RSASSA-v1.5 w/ SHA-384 |
| RSA512 | * | RSASSA-v1.5 w/ SHA-256 |
| ES256 | -7 | ECDSA w/ SHA-256 |
| ES384 | -8 | ECDSA w/ SHA-384 |
| ES512 | -9 | ECDSA w/ SHA-512 |
| PS256 | -10 | RSASSA-PSS w/ SHA-256 |
| PS384 | * | RSASSA-PSS w/ SHA-384 |
| PS512 | -11 | RSASSA-PSS w/ SHA-512 |
| RSA1_5 | * | RSAES v1.5 Key Encryption |
| RSA-OAEP | -2 | RSAES OAEP w/ SHA-256 |
| A128KW | -3 | AES Key Wrap w/ 128-bit key |
| A192KW | -4 | AES Key Wrap w/ 192-bit key |
| A256KW | -5 | AES Key Wrap w/ 256-bit key |
| dir | -6 | Direct use of CEK |
| ECDH-ES | * | ECDH ES w/ Concat KDF as CEK |
| ECDH-ES+A128KW | * | ECDH ES w/ Concat KDF and AES Key wrap w/ 128 bit key |
| ECDH-ES+A192KW | * | ECDH ES w/ Concat KDF and AES Key wrap w/ 192 bit key |
| ECDH-ES+A256KW | * | ECDH ES w/ Concat KDF and AES Key wrap w/ 256 bit key |
| A128GCMKW | * | AES GCM Key Wrap w/ 128 bit key |
| A192GCMKW | * | AES GCM Key Wrap w/ 192 bit key |
| A256GCMKW | * | AES GCM Key Wrap w/ 256 bit key |
| PBES2-HS256+A128KW | * | PBES2 w/ HMAC SHA-256 and AES Key wrap w/ 128 bit key |
| PBES2-HS384+A192KW | * | PBES2 w/ HMAC SHA-384 and AES Key wrap w/ 192 bit key |
| PBES2-HS512+A256KW | * | PBES2 w/ HMAC SHA-512 and AES Key wrap w/ 256 bit key |
| A128GCM | 1 | AES-GCM mode w/ 128-bit key |
| A192GCM | 2 | AES-GCM mode w/ 192-bit key |
| A256GCM | 3 | AES-GCM mode w/ 256-bit key |
| name | number | description |
|---|---|---|
| EC | 1 | Elliptic Curve key Type |
| RSA | 2 | RSA Key type |
| oct | 3 | Octet Key type |
| P256 | 4 | EC Curve P256 (NIST) |
| P521 | 5 | EC Curve P521 (NIST) |
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.
| name | key | CBOR type | registry | description |
|---|---|---|---|---|
| kty | 1 | tstr / int | COSE General Values | Identification of the key type |
| use | * | tstr | deprecated - don’t use | |
| key_ops | * | [* tstr] | ||
| alg | 3 | tstr / int | COSE Algorithm Values | Key usage restriction to this algorithm |
| kid | 2 | bstr | Key Identification value - match to kid in message | |
| x5u | * | tstr | ||
| x5c | * | bstr* | ||
| x5t | * | bstr | ||
| x5t#S256 | * | bstr |
;key_keys kty=1 key_kid=2 key_alg=3
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
| key type | name | key | CBOR type | registry | description |
|---|---|---|---|---|---|
| EC | crv | -1 | int / tstr | Pull from general value registry | |
| EC | x | -2 | bstr | ||
| EC | y | -3 | bstr | ||
| EC | d | -4 | bstr | ||
| RSA | e | -1 | bstr | ||
| RSA | n | -2 | bstr | ||
| RSA | d | -3 | bstr | ||
| RSA | p | -4 | bstr | ||
| RSA | q | -5 | bstr | ||
| RSA | dp | -6 | bstr | ||
| RSA | dq | -7 | bstr | ||
| RSA | qi | -8 | bstr | ||
| RSA | oth | -9 | bstr | ||
| RSA | r | -10 | bstr | ||
| RSA | t | -11 | bstr | ||
| oct | k | -1 | bstr |