Adding method for decrypt the encrypted text.

[shagihan]

Purpose

Since there is no method for decrypting the encrypted text with the cipher-tool, Created a new method to decrypt.

Approach

Users can use -Ddecrypt parameter when running the cipher-tool and by providing necessary parameters could decrypt encrypted text.

[CLAassistant]

All committers have signed the CLA.

[sachithKay]

Cipher-tool is only focussed on encryption. Decryption is handled at runtime. If we let users to run the cipher tool and retrieve the password, wouldn't it create a vulnerability?
What would be a proper use case for this?

[shagihan]

1. Cipher tool is not publicly accessible and this is an option only used by the system administrators who is having the the file system access and having execution permissions.
2. Even to run the decryption, It's required to have the password of the keystore, Which used to encrypt the passwords with cipher tool. In that case, If someone knows the password of the keystore, It's just running several commands to decrypt the cipher text and extract the passwords.

The intention of this modification is just to make some convenience.