This entry documents the basic process for setting up CRAM-MD5 authentication for Dovecot.
Firstly, you need to enable the mechanism and specify a passwd database file in Dovecot. The mechanism and passdb file are specified in the dovecot.conf configuration file, on a Red Hat or similar system this is located in the /usr/local/etc/ directory.
auth default {
# Space separated list of wanted authentication mechanisms:
# plain login digest-md5 cram-md5 ntlm rpa apop anonymous gssapi
mechanisms = plain login cram-md5
# passwd-like file with specified location
passdb passwd-file {
# Path for passwd-file
args = /etc/cram-md5.pwd
}
….
}
You see that I’ve added the cram-md5 mechanism to the mechanisms statement and then added a passdb file, /etc/cram-md5.pwd.
Next, you need to create this passdb file and set appropriate permissions.
# touch /etc/cram-md5.pwd # chmod 0600 /etc/cram-md5.pwd
After creating the file you need to add your users and hashed passwords to the passdb file. The users and passwords are added in the format:
username:passwordhash
Dovecot has a utility that allows you to convert passwords to the appropriate hashes. This utility is called dovecotpw and is installed into the /usr/local/sbin directory or is available in the source package in the src/util directory. You can run dovecotpw like so:
# dovecotpw
Enter new password: password
Retype new password: password
{CRAM-MD5}26b633ec8bf9dd526293c5897400bddeef9299fad
Enter the user’s password when prompted and it will be converted and outputted as a hash. The default hashed output is in the CRAM-MD5 scheme (old Dovecot versions called the scheme HMAC-MD5, which is confusing because it's not the real HMAC-MD5). You can change the scheme of the outputted hashes using the -s command line switch.
Now add the generated password to the passdb file, /etc/cram-md5.pwd.
username:{CRAM-MD5}26b633ec8bf9dd526293c5897400bddeef9299fad
Finally, restart Dovecot and test authentication by enabling the appropriate mechanism in your email client. For example, to enable CRAM-MD5 authentication in Thunderbird you need to check the “Use secure authentication” checkbox in the Account Settings page.
I recommend that you also use TLS/SSL to encrypt the authentication process as well.