If you lose or never receive the email containing the decrypt key, it will be impossible to retrieve the decrypt key, it will be impossible to retrieve the decrypted card number.
Data is automatically encrypted when it's written to the hard disk and automatically decrypted before being loaded into memory.
Information encrypted with the public key cannot be decrypted without the corresponding private key, which only Velocity Pay has.
Once a message is encrypted with the public key it cannot be decrypted with the public key but only by the corresponding private key.
She checked the comms from the mountain and fed the decrypted messages back into the computer.