While, in principle, PSS is better than PKCS#1 v1.5, and
algorithm-specific keys are better than mixing them up, RSASSA-PSS was
so badly mis-standardized in RFC 3447 and RFC 4055 that this is not
worth it. Any marginal benefits one might get from PSS is completely
overshadowed by the mountain of unforced errors those two RFCs made.
Applications are better off just using ECDSA.
Nonetheless, it is a thing we are now supporting. Add off-by-default
support for EVP_PKEY_RSA_PSS, only using the SHA-256 parameter set. In
OpenSSL's implementation, the underlying RSA object stores an
RSA_PSS_PARAMS, though the RSA-level APIs don't enforce the parameters,
only the EVP-level APIs do. For now, since the SHA-256 parameters are
the only ones we support, I have not bothered adding extra state to the
RSA object. If we need to add more parameters, we can store the
rsa_pss_params_t enum on the RSA object. (Preferably after we've split
the BCM and non-BCM halves of the RSA object.)
This support is off by default and must remain so. We have a bit of a
mess API-wise: OpenSSL made EVP_PKEY_get0_RSA work with
EVP_PKEY_RSA_PSS. This is plausible in that applications may want to
inspect RSA components and that is, for now, the API to do so. However,
existing callers generally assume a non-NULL EVP_PKEY_get0_RSA return
implies EVP_PKEY_RSA. Changing this will break those callers.
Thus the opt-in not only limits a badly-designed key type, but also
prevents existing callers from being exposed to this unexpected state.
These keys are not wired up to libssl and we have no plans to do so.
Bug: 384818542
Change-Id: I4d99be86ce1d891a2e50335ef097913707ede55a
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/81656
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
David Benjamin
be4e218c9e