how can i create signed smime with client user smartcard

Question

We have a web project. We get client's public key from his/her smartcard by an applet. But we can not get smartcard's private key. We have only client's public key. So, we can not create smime which is signed by client. What can we do? Can we create a signed smime by public key?

Answer 1

To sign any data including email, you need a private key of a signer.

It doesn't make any sense to sign email using public key, as it is available to every one. Which means that the signature doesn't prove, that it is the signer that signed the email.