"To decrypt the message" means to translate or convert an encoded or secret message back into its original form that can be easily understood. Full definition
This all might sound like a lot to handle, but 10 untrained users were able to decrypt messages using the technique. (sciencemag.org)
While Apple has been waging a very public battle, it turns out that Canadian police have been decrypting the messages of millions of Blackberry users. (gizmodo.com)
But these keys are sent to a central server along with user passwords in plain, unencrypted text, meaning that anyone who can break into the server can decrypt the message traffic, he said. (businessinsider.com)