.KEYCHAIN File Extension

Keychain file created by Apple Keychain, a program bundled with Mac OS X that stores authentication information; contains an encrypted collection of resource authentication data, such as passwords, certificates, and private keys.

KEYCHAIN files are used to automatically authenticate users after they have checked the option to remember authentication information. They are used for websites, SSH accounts, FTP files, and wireless networks.

KEYCHAIN files are commonly found with the name login.keychain.