Is javascript RSA signing safe?

Is javascript RSA signing safe?

I'm currently working on a secure open source messaging system
(https://github.com/DSMNET/DSMNET). Currently I'm using the cryptico.js
(https://github.com/wwwtyro/cryptico) library to encrypt all the messages
sent.
Now to authenticate user's my server will send a random string and the
client will encrypt the string and sign it. The server will check if the
signature matches the publickey stored for the user. User's will generate
their public and private key with their password.
I would like to know if using javascript RSA and using RSA signatures to
authenticate is safe or can people forge RSA signatures.
Thanks