HMAC validate and compute might not share the same context.

[laurencelundblade]

Not sure all crypto libraries will use the same context for mac_validate and mac_compute like PSA. It is probably not a safe assumption. Perhaps look at what OpenSSL does. Probably need to have two t_cose_crypto_hmac_update() functions, one for compute and one for validate because not all crypto may be the same as PSA

[laurencelundblade]

#276