Created by Apple Inc., Keychain is a password management system for Mac OS. It contains many different types of data from passwords to certificates and secure notes. It can also store a title and URL. However, passwords and secure notes are the only data that is encrypted. This keychain idea was initially created for Apple’s email system, PowerTalk. Once PowerTalk ended, Steve Jobs began using Keychain for the Mac operating systems. It is now included on all the latest versions of the Mac OS from Mac OS 9 to Mac OS X.
In addition to the problem described above, i.e. the lack of the appropriate application to support the .KEYCHAIN file, there may be several reasons that cause problems with opening and operation of the data format:
A quite common problem is the lack of application in the appropriate version. Even if you have an application, with the help of which you should open the .KEYCHAIN file, you may have a problem with it because of its version. Perhaps in previous versions the application has not yet supported the .KEYCHAIN file, so download the update and check again.
If you have already installed the appropriate application, and it is the correct version, the file may not open correctly, because the operating system does not have information that this program supports the file. So you need to "show" which program the computer should use. To do this:
It also happens that the file you want to open is corrupt and therefore there is no such possibility. In this situation, you should find its different version, or ask a person from whom you got, to send it again.