Digest passwords enable an application to avoid storing and even transmitting the password in a form that someone can read.
A digest of a cleartext password is calculated when it is passed through a one-way function that consistently produces another series of characters, digestPassword = digester(username + ":" + realm + ":" cleartextPassword). The function is "one-way" because the digestPassword cannot be used to reverse-engineer the original password.
Digest passwords can be used in two places: storage and transmission. Digest passwords in storage means that the password is stored in a digested form, for example in a database or in a file. Digest passwords in transmission means that the client (usually a web browser) creates the digest and submits the digest password to the web server.
Storing digest passwords is so important for security purposes that the Resin authenticators default to assuming that the passwords are stored in digest form.
The important advantage is that a user's cleartext password is not as easily compromised. Since the password they use (the "cleartext" password) is not stored a malicious user cannot determine the password by gaining access to the database or other backend storage for the passwords.
Resin's authenticators use "MD5-base64" and a realm "resin" to digest passwords by default.indicates that the MD5 algorithm is used. is an encoding format to apply to the binary result of MD5.
Some examples are:
In the above example the digest of "harry/quidditch" is different than the digest of "hpotter/quidditch" because even though the password is the same, the username has changed. The digest is calculated with digest(username + ":" + realm + ":" + password), so if the username changes the resulting digest is different.
Of course, storing the digest password is a bit more work. When the user registers, the application needs to compute the digest to store it.
The class class com.caucho.http.security.PasswordDigest can be used to calculate a digest.
When using the form login method or the HTTP basic authentication login method, the password submitted is in cleartext. The Resin authenticator will digest the password before comparing it to the value retrieved from storage. The message is transmitted in cleartext but is stored as a digest. This method provides only half of the protection - the password is not protected in transmission (although if the form submit is being done over an SSL connection it will be secure).
The HTTP protocol includes a method to indicate to the client that it should make a digest using the password. The client submits a digest to Resin instead of submitting a cleartext password. HTTP digest authentication protects the password in transmission.
When using HTTP digest, Resin will respond to the browser and ask it to calculcate a digest. The steps involved are:
The advantage of this method is that the cleartext password is protected in transmission, it cannot be determined from the digest that is submitted by the client to the server.
Although it is not advised, Resin's authenticators can be configured to use passwords that are not in digest form.
Authenticators are not defined by the Servlet Specification , so the ability to use passwords stored as a digest depends upon the implementation of the Authenticator that the application server provides. MD5-base64 is the most common form of digest, because it is the default in HTTP digest authentication.
The use of <auth-method>DIGEST<auth-method> is defined in the Servlet Specification and implemented in most application servers.