Can the RSA PSS salt length be changed?

[Petr Gotthard <petr.gotthard@centrum.cz>]

Hello,
I have a question concerning the TCG specification.

OpenSSL has a function EVP_PKEY_CTX_set_rsa_pss_saltlen() that be used to set the RSA PSS salt length. Some implementations don't use the maximum possible salt length, but use a shorter value, e.g. set the salt length to the digest length (RSA_PSS_SALTLEN_DIGEST).
https://www.openssl.org/docs/manmaster/man3/EVP_PKEY_CTX_set_rsa_pss_saltlen.html

The TCG specification (Part 1, Section B.7) on the other hand says: For both restricted and unrestricted signing keys, the random salt length will be the largest size allowed by the key size and message digest size.

Does this mean that a TPM2.0 cannot handle shorter RSA PSS salt lengths, i.e. that the EVP_PKEY_CTX_set_rsa_pss_saltlen() function can never be implemented using any TPM? This might cause compatibility issues.


Regards,
Petr