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I recently migrated my IMAP server from Courier-IMAP to Dovecot. It’s part of a whole simplification process I am engaging in. I cut-over the IMAP server and then last week enabled the Dovecot authentication in Postfix to allow me to stop using a separate SASL daemon for authentication. Now both SMTP and IMAP are authenticated from the one source – Dovecot.
But one thing I discovered when setting up Dovecot is that there is very limited documentation on using CRAM-MD5 authentication with Dovecot. As a result I am going to quickly document the process I used to get this up and running.
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 my 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
}
….
}
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:
user: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:
Retype new password:
{HMAC-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 HMAC-MD5 scheme (which is appropriate for CRAM-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.
kartar:{HMAC-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.
Obviously I recommend that you use TLS/SSL to encrypt the authentication process as well.
