I have idea:
- choose any address that contained in both the ciphered wallet and unencrypted backup
- extract private key for address from unencrypted backup
- extract ciphered private key from ciphered wallet
- compare two extracted strings and get password for the wallet
I have superficial knowledge of cryptography, but this should work

Anyone know about software that can do what I described?
This is called a "known-plaintext attack". Every wallet I've seen to date uses the AES cipher which is believed to be invulnerable to this type of attack, sorry:
https://en.wikipedia.org/wiki/Known-plaintext_attack#Present_day 
Do you have any recollection of your password? If so, you might be able to use one of the tools in this thread, or you could hire a service to try to recover your password.