Upgrade to MacOS Tahoe 26.5 causes Key Chain Access password to not work

Typically your keychain access password is the same as your login password unless you deliberately chose to make it different.

Type ⌘Command+Space to open Spotlight, type Keychain Access to find and launch the Keychain app. Now select Settings->Reset Default Keychains. Note that all data in your keychain will be lost.

Here are additional links that may help.

If your Mac keeps asking for your keychain password - Apple Support

If you need to update your keychain password on Mac - Apple Support

I've had the same problem and eventually got round it by restoring the broken keychain from a TimeMachine backup made before the update. Open the restored keychain with Keychain Access and you will be able to see the contents by entering your password in the usual way.

In my case the keychain that broke was created on an Intel Mac and became a Custom Keychain called my.login alongside the new default keychain called login when I switched to Apple silicon (M series). All worked fine until OS 26.5

Be warned that if you restart the keychain will break again, but you can restore from backup once more. Here's the reason the problem occurs according to Claude:

"macOS 26.5's securityd is rejecting the backup keychain file as a "non-keychain file" because it doesn't recognise the legacy kych format version. The system is treating it as invalid, which explains the "Invalid argument" errors and why it breaks on restart — securityd is actively invalidating it when it tries to process it at login.

The legacy keychain format is essentially incompatible with how 26.5's security daemon handles keychain files now."

This is an instance where an LLM is your friend – if you're unsure of what to do just paste the above into one of the major models to give context and you can be guided through the steps.

to add — if you changed your admin password at some point — the keychain psswd does not follow suit, it retains the original password when it was set up...if that is your issue(?)

You wan to leave that padlock unlocked for trouble free—

The Password.app is the new password manager

Passwords User Guide

yantzi wrote:

I have never changed my admin password. It has been the same for many years and through many MacOS upgrades and this is the first time I have had this problem.

"Upgraded to MacOS Tahoe 26.5 " from what previous macOS...(?)