A couple of days ago I wrote about universal ElGamal ciphertexts and about the importance of digital signatures. Although the story of a rather unremarkable piece of malware served us well as an example, it was not an example a reader could easily relate to or get their hands on. This time, I provide real-world examples in the form of actual messages and keys made of genuine bits.
ElGamal encryption is a mandatory part of OpenPGP, a comprehensive cryptographic standard also used to secure electronic mail. Until about 2009, ElGamal was the default public-key encryption method of GNU Privacy Guard, a free software implementation of OpenPGP. This text is about universal OpenPGP ciphertexts, fake encryption keys silently disabling encryption and about the importance of digital signatures.
In typical applications of cryptography, there usually are several distinct parties involved in a protocol. That might be part of the reason why cryptography has become so complicated. Even in simpler scenarios, where the sender and the recipient of a message are essentially the same person, there are applications for the arguably more advanced public-key primitives. There is also plenty of room for mistakes to be made.
Mallory has managed to install malware onto a machine she normally has no business of accessing. To carry out her evil plans, she has set up a way to control the victim machine remotely. She is able to send commands to and receive responses from the malware running there. This text is about the way Mallory applies cryptography to secure her messages.
It was recently revealed that the network of the Swiss company RUAG had been compromised. The GovCERT unit of the federal Reporting and Analysis Centre for Information Assurance MELANI was involved in the investigation and released a technical report on the espionage case.
On a few dozen pages, the document explains how the attack was probably carried out. The report also provides information on the malware used by the attackers. There is a rather remarkable five-page section on how a particular piece of malware implemented cryptography. Let us have a closer look at what GovCERT had to say and what was missing.