Try the following and see if it fixes the issue for you;
Shutdown your Mac
Then, press and hold the “Option” key as soon as you hear the startup chime.
When the boot menu appears, release the Option key and and select the “Recovery” volume in the boot menu.
Wait for “OS X Utilities” menu to appear (DO NOT RE-INSTALL)
Click on the “Utilities” option in the menubar the the top of the screen and select “Terminal”
Type the following at the prompt:
and press Return on the keyboard.
Select the Macintosh HD volume and the user account. To change the password, type it in both places, and a hint, then click the Save button.
Restart your Mac and, hopefully, login with a working keychain password.If you still have concerns, simply reply back before rating. I'll be more than happy to work with you further. Hopefully, this info will answer your question
. When you are satisfied, please give my answers a positive rating. You are judging my personal service only (not this website or your issue) and positive ratings assure I am credited for my time.
Thanks and good luck,