Keystore error with mismatching key and keystore passwords for certificates.

This problem is reproducible using Java Keytool Command:

For the below code sample, let's say that our password for the "key password" was set to 1234567 initially. Salesforce only requests the "keystore password" be set, so Salesforce needs to be able to decrypt the certificates with this alone by having the passwords match. Thus, when we run the below;

keytool -importkeystore -srckeystore keystore.jks -destkeystore keystore-in-pkcs12.p12 -deststoretype PKCS12 
Enter destination keystore password: <123456> 
Re-enter new password: <123456> 
Enter source keystore password: <123456> 
Enter key password for <salesforce> <123456> 
keytool error: java.security.UnrecoverableKeyException: Cannot recover key 

The "keystore" and "key" passwords do not match, so it will throw an 'UnrecoverableKeyException' error.

Conclusion:
In order to avoid this error, ensure that the Private Key and the Keystore are encrypted using same password.