OS X used to provide a keychain first aid feature. Now this has gone, this is the only way that you can try to repair a defective keychain: create a new one.
passwords
When the password used to log in and that to unlock your login keychain become different, you may be asked to keep entering your keychain password. Here’s how to fix this, and more.
Coupled with FileVault’s whole disk encryption, this can stop others from accessing your data. But there are disadvantages too.
Which is better – a 6 digit PIN, or a shorter alphanumeric password – for protecting your iPhone?
Have you ever entered the password for your Mac instead of that for your Apple ID? This should help make it clearer which you need to use.
Why do I have to enter my keychain password every time my Mac starts or restarts?
Can I change password entry dialogs to show the correct characters instead of blobs?
When I set up my iPad WiFi, it asks for a password and a user name. How can I find out what my user name is?
Businesses are often built on trust, and one of the most fundamental elements of trust must be in the accuracy of the data on your Mac. How should you ensure that your files remain true and correct?
Everywhere that you go you need user names, passwords, and other means of proving your identity. In OS X and iOS these are normally stored in a keychain.
The Eclectic Light Company 