Secure communication with Stunnel
Stunnel is an SSL encryption wrapper that allows what are normally plain text and insecure communications to be encrypted during transmission. Stunnel recently went through some major changes and the current version (4.x) has a completely different architecture than previous versions. In this article I will be dealing exclusively with the new version.
One of Stunnel's most common uses is encrypting communications between POP or IMAP mail servers and e-mail clients. Both of these protocols require users to authenticate themselves with a username and a password. In the majority of cases, these usernames and passwords are the same ones as they would use for logging into the machine locally or remotely via SSH. Without using Stunnel to encrypt this data, anyone intercepting the transmission could now log into your server and gain elevated privileges much easier than a local exploit would require.
By Barry O'Donovan at the Linux Gazette.
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