The 'jsrsasign' (RSA-Sign JavaScript Library) is an opensource free cryptographic library which supports RSA/RSAPSS/ECDSA signing/validation, ASN.1, PKCS#5/8 private key X.509 certificate and CRL library in pure JavaScript.
Public page is http://kjur.github.com/jsrsasign .
Your bugfix and pull request contribution are always welcomed :)