Q: password to unlock your iphone backup file

OLd iTunes password (password that was used initially on phone) worked. thanks.

This worked for me! thanks

this is the the only way out ,try to remember your very first password when you made iTunes account and finger crossed it will work(worked for me) goodluck  .

mine was my phones 6 (or four) digit pass code. also make sure you have no pending emails that need to be verified. Like ones you have as back ups as these were my issues twice. I tried all other older passwords and t didn't work but the phone unlock screen worked.

USE 1234

!!!!

100% The first password that was used to set up iTunes

Unless legitimately it had been encrypted recently and you changed the password

I know you posted this 4 years ago, but it helped me so much today. I really love you

The "password," WHICH I NEVER SET UP for iPhone backup, despite what good ol' Mr. Know-It-All Finch says, was my 4 digit screen unlock code.

thanks, the old password works for me too.

Well here's my tuppence worth - today I went and bought myself a new iPhoneSE. Before I set off for the Apple Store, I backed up my iPhone5 to my work laptop's iTunes (this is a PC laptop running win7, for what it's worth).  When I tried to restore that backup to my brand new iPhoneSE, I also got the prompt to enter a password to unlock the backup.
Here is the thing - I have NEVER backed up the phone to this laptop previously, it was always backed up at the iMac at home, so I know for definite that I hadn't entered a backup encryption password previously, and this morning I wasn't asked for a password when I performed (what the laptop version of iTunes considers) the first and only iPhone backup. 
I've tried my iTunes (AppleID) account password, the admin user password for the machine, the passcode for the phone, none of these unlock the backup. So where has the encryption backup  password come from?

ADDENDUM
Since posting the above, I have solved where the password comes from, it's actually held on the phone.  It is not dependent on which instance of iTunes you use to back up.Thankfully, the password was in my mac's keychain, so I am happily restoring now

That makes some sense to me.

I bought a new laptop

installed itunes

Ran a backup of my 6plus (encrypt backup was already set and couldn't be unset...???...not sure why)

it did not ask for a password to be set.

new 6plus from applecare today, Asks for password to unlock backup.....What?  No password was ever set or requested on this virgin machine, virgin iphone.

I did the "every password I ever used" route.  One finally worked. 

Must have stored it in my icloud keychain.  Go figure.  Always test backups before you trust them.

Doc

Yes it worked for me too. I used my iTunes account password to restore the iPhone backup.

Message is misleading: "password to unlock your iphone backup file" makes you think you need to enter the iPhone passcode.

Since posting the above, I have solved where the password comes from, it's actually held on the phone. 

It is not dependent on which instance of iTunes you use to back up.Thankfully, the password was in my mac's keychain, so I am happily restoring now

Your first point is not accurate . Your second is. The only password/passcode entries stored on a physical phone are device passcodes and restrictions passcode.

An encrypted password for an iTunes backup is stored within the backup file itself. That is why if you can't recall it, you have to set up a device as new and "break" the chain. This also why the version or even installation of iTunes is not part of the issue. You can "move" backup file from one PC to another. The encrypted password would go with the backup file.

Yes!  Thanks for the info.. I entered my oldest iTunes password which I had setup when bought the very first generation of iPhone and it worked!!!