Java Security

Hi,

I need to verify digital signature created by iexplorer capicom or by firefox window.crypto.signText.

I already created java code that makes this using the sun.security.pkcs.PKCS7 class, but now i'need to validate a signature made with a certificate that only have the non-repudiation bit active (with my code i get the following exception "java.security.SignatureException: Key usage restricted: cannot be used for digital signatures") and the CA certificate have 4098 bits.

I'm using the java 142 and i'm trying to use the bouncycastle package to solve my problems, but i don't understand how can i do this.

Anyone already made this?

Thanks in advanced
rjc