t_cose

Introduction

t_cose is a partial implementation of the COSE standard (RFC 8152). COSE is quite a large standard so a full implementation of all of it is a large undertaking. This implementation is starting out as just enough for attestation and maybe CWT (Cbor Web Token) which is very similar.

As it may grow to support more of COSE over time, it is structured with that in mind.

It is also trying to be portable, the most interesting part of which is interfacing with the libraries for performing cryptography and access cryptographic keys.

Source files

The following files are more or less the public interface.

t_cose_common.h
t_cose_sign1.h
t_cose_sign1_verify.h

The rest of the files are internal source files that callers should not depend on.

t_cose_defines.h contains contants from RFC 8152 that are part of the COSE standard. It should never have anything else in it.

t_cose_util is some utilities and code common to signing and verification. Both signing and verifcation depend on it.

t_cose_crypto is the crypto porting layer. Generally the .h file should not need to change for a new platform. The .c file will be changed lots for each new platform.

Dependency and Portability

t_cose is attempting to be very portable and have a minmum number of #ifdefs. It is designed to run 64-bit and 32-bit machines.

It uses a minimum number of standard C libraries, mostly just , and .

It uses QCBOR for CBOR encoding and decoding. QCBOR is very portable.

Cryptography and Keys

There is a cryptographic adaption layer that provides the following:

Impedence match of parameters passed to/from the crypto
Management of algorithm identifiers
Management of error codes
Management of key identifiers

It is framed for the needs of t_cose, and is not trying to be any kind of general crypto API.

Question

Q: How many crypto APIs does it take to screw in a light bulb? A: One more than it takes to screw in a light bulb.

Copyright and License

BSD-3-Clause license

Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

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