db backend is missing the public exponent for private keys

[gumulka]

When using openssl with pkcs11-provider to sign something using softhsm with the db-backend, OpenSSL fails with

+ openssl cms -sign -inkey 'pkcs11:token=store;object=test;pin-value=1111' -signer /openssl_error/files/cert.pem -in /openssl_error/files/test.input -out /openssl_error/files/test.output
Error writing CMS output
4097AC5EB97F0000:error:0200008C:rsa routines:RSA_setup_blinding:no public exponent:../crypto/rsa/rsa_crpt.c:139:

This does not happen, if the files backend in softhsm is used to sign the file.

To Reproduce

I created to following shell script to reproduce the bug: testcase.sh

It was tested with softhsm 2.7.0, with db-backend enabled.

Applications used

• Device: softhsm 2.7.0 (also 2.6.1)
• PKCS11 Driver version: pkcs11-provider 1.2 (also 1.1 and 1.0)
• Application openssl 3.5.5 (also 3.5.4)

Specification

The relevant part of the spec seems to be https://docs.oasis-open.org/pkcs11/pkcs11-spec/v3.2/pkcs11-spec-v3.2.html#_Toc195693098

As a general guideline, private keys of any type SHOULD store sufficient information to retrieve the public key information. In particular, the RSA private key description has been modified in PKCS#11 V2.40 to add the CKA_PUBLIC_EXPONENT to the list of attributes required for an RSA private key. All other private key types described in this specification contain sufficient information to recover the associated public key.

[jluebbe]

I've debugged this further. By default, pkcs11-provider uses C_CopyObject to cache keys. When disabling caching via pkcs11-module-cache-keys = false in the openssl.cnf, the issue dissappears.

When looking at Token::decrypt with a debugger, it seems that the encrypted ByteStrings have length 0, so I suspect that something fails during the copy operation, but I wasn't able to actually find the cause.

[bukka]

This looks like a bug. It might take me some time as I have to prioritise paid OSS work but hopefully will manage to find some free time to debug it.