Certificate Profile - Signature Algorithm

[tlull]

Hello,
we try to increase the security of our certificates and decided to use Ed25519 as the key algorithm.
We have thought that it would be nice when in addition Ed25519 could be used as the signing algorithm.
I'm running EJBCA version 7.11.0.

The issuing CA uses SHA256WithRSA as signing algorithm. But it is possible to change the
signature algorithm within a certificate profile by changing the field "Signature Algorithm".
In the appropriate crypto token I have created a key with algorithm Ed25519.
The documentation "EJBCA CA Concept Guide -> Certificate Authority Overview" describes
how multiple signing algorithms can be connected with specific keys:
"A CA is defined to use several key pairs which are mapped to a purpose. .... Note that the same alias can be used for several mappings."
But I cannot find that within the CA configuration.
For the certificate profile field "Signature Algorithm" there is no documentation at all.

When I try to enroll a certificate I get the following exception:
org.cesecore.certificates.certificate.CertificateCreateException: org.bouncycastle.operator.OperatorCreationException: cannot create signer: cannot identify EdDSA private key
So my question is, is it possible to use a different signature algorithm than defined by the issuing CA?

Kind regards,
Torsten

[primetomas]

So your CA uses RSA keys, which means it can obviously not sign with Ed25519, RSA keys are only good for RSA signatures as we know. A single CA can not have multiple CA signing keys in use at the same time, that would become very complicated in path building etc for relying parties. Publicly trusted Web PKI (SSL) CAs use different Roots for RSA and EC, it's best practice.

If you want to use a CA with Ed25519 I would recommend to create a new CA for that.
You could renew your existing CA, and switch signature keys and signature algorithms. That would retire your use of SHA256WithRSA and switch to Ed25519 completely.

(PS: to my knowledge there is nothing today that says Ed25519 is more secure than RSA, it more depends on the use case which one you want to use).

[primetomas]

Signature algorithm in the certificate profile is normally "same as CA". The option to choose there is if you have an old CA with say SHA1WithRSA, but want to sign the end entity certificates with SHA256WithRSA. The signature algorithm still have to match the CAs key type.

[tlull]

Hello Tomas,
many thanks for your quick explanation.

Kind regards,
Torsten