-- Gilles Peskine Mbed TLS developer and PSA crypto API designer P.S. When I'm working on Mbed TLS and using a shell prompt to calculate or verify values (usually with openssl or python/cryptodome), I usually use hex/binary conversion, and DER to encode asymmetric keys. On 14/05/2020 13:56, Kevin Townsend via psa-crypto wrote: > Hi, > > Working on some cryptography demos for Zephyr, now that TF-M support > was fully merged in for the upcoming 2.3 release, I've put some test > code together that: > > - Generates a permanent persistent key (prime256v1) > - Displays the public key based on the private key above (in hex format) > - Calculates the SHA256 hash of a payload > - Signs the hash with the persistent key > - Verifies the signature using the public key > - Destroys the key > > https://gist.github.com/microbuilder/a326cc6b935f87f413d89e44f9d3de05 > > An important part of the hash/sign/verify workflow is of course > verifying the signature on the receiving end, which requires access to > the public key generated on the device (perhaps a new key was randomly > generated when the device first boots, etc.). > > We can currently derive the public key in DER format with the existing > API, but it seems like a helper function to convert to PEM would make > this export process easier, since you could then just copy and paste > the text output directly for provisioning or debug purposes. > mbedcrypto 3.1.0 already has a library/pem.c utility function for this > that could be exposed: mbedtls_pem_write_buffer > > In general, I think enabling the import and export of PEM data, not > just DER, would make the process of dealing with keys during > provisioning easier. > > I didn't find any references to PEM in the PSA Cryptography API, but > perhaps I'm missing some obvious already existing means to convert to > PEM, or is this something other people see any value in having? > > Being able to copy and paste PEM data (versus DER which can't be > copy/pasted), then save it as a file, for example, would make working > with openssl easier, such as the commands described here where we > could use the extracted PEM data to verify the signed data from the > command line: > https://gist.github.com/microbuilder/a326cc6b935f87f413d89e44f9d3de05#file-p... > > Any thoughts on the idea, or perhaps it's already been added and I'm > simply missing it? > > It's easy to add this at the NS application level as well, of course, > but it does seem like a useful enough operation that it should be > available in S world when requesting key data. > > Best regards, > Kevin Townsend >