Java script throwing error "Crypto.js" not defined for the code var md5Header = CryptoJS.MD5(request.data).toString();

We need to generate Hmac.md5 session key for which added the Javascript code "var md5Header = CryptoJS.MD5(request.data).toString();"
when executing getting error message ReferenceError: "CryptoJS" is not defined.
Looks like some library file missing, where to get and how to add them.