| Internet-Draft | COSE Algorithms | November 2019 |
| Schaad | Expires 20 May 2020 | [Page] |
The CBOR Object Signing and Encryption (COSE) syntax [I-D.ietf-cose-rfc8152bis-struct] allows for adding additional algorithms to the registries. This document adds one additional key wrap algorithm to the registry using the AES Wrap with Padding Algorithm [RFC5649].¶
This note is to be removed before publishing as an RFC.¶
The source for this draft is being maintained in GitHub. Suggested changes should be submitted as pull requests at https://github.com/cose-wg/X509 Editorial changes can be managed in GitHub, but any substantial issues need to be discussed on the COSE mailing list.¶
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The CBOR Object Signing and Encryption (COSE) syntax [I-D.ietf-cose-rfc8152bis-struct] is defined to have an object based set of security primatives using CBOR [I-D.ietf-cbor-7049bis] for use in constrained environments. COSE has algorithm agility so that documents like this one can register algorithms which are needed.¶
In this document we add the AES Wrap with Padding algorithm to the registry and describe how to use it.¶
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 section is to be removed before publishing as an RFC.¶
The AES Key Wrap with Padding is defined in [RFC5649]. This algorithm uses an AES key to wrap a value that is a multiple of 8 bits. As such, it can be used to wrap not only the key sizes for the content encryption algorithms, but additionally it can be used to encrypt off size keys that can be used with the keyed hash functions or key derivation functions. The algorithm uses a single fixed parameter, the initial value. This value is fixed in section 3 of [RFC5649], this is a different value from that used for the AES Key Wrap algorithm of [RFC3394]. There are no public parameters that very on a per-invocation bases. This algorithm does not support additional data and thus the protected header field MUST be empty.¶
When using a COSE key for this algorithm, the following checks are made:¶
| Name | Value | Key Size | Description |
|---|---|---|---|
| A128KW-Pad | TBD1 | 128 | AES Key Wrap w/padding and a 128-bit key |
| A192KW-Pad | TBD2 | 192 | AES Key Wrap w/padding and a 192-bit key |
| A256KW-Pad | TBD3 | 256 | AES Key Wrap w/padding and a 256-bit key |
The shared secret needs to have some method to be regularly updated over time. The shared secret is the basis of trust.¶