I’ve lost my password for bitcoin wallet

But I have unencrypted backup of the wallet that was made a year ago.
Unfortunately, bitcoins stored on addresses that contained only in ciphered wallet, not in unencrypted backup.
But some addresses are contained both in the encrypted and unencrypted wallet backup

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

my idea is feasible?
Anyone know about software that can do what I described?
Can anyone create such software for reward?