Introduction to Cyber-Warfare - Proiect SEMPER FIDELIS

STOLEN KEYING MATERIAL163of the system. Due to the incredibly broad nature of this attack surface, vulnerabilities in theoperating system kernel have historically been plentiful and are generally described as “privilegeescalation vulnerabilities.”STOLEN KEYING MATERIALDuqu and Stuxnet turned heads in the computer security community by making use ofstolen code-signing keys. Starting with Windows Vista, Microsoft began requiring that anycompany or individual who wanted to create a device driver for Windows had to use theglobal Public Key Infrastructure (PKI) to “sign” device drivers. Such a signature would attestthat the device driver was actually produced by the company that produced it.Digitally signing a message, whether or not that message is human-readable text or thebinary code of a device driver, allows for verification that the text has not been altered. Withsuch a set of rules in place, the operating system can guarantee that only code that was signedby appropriate parties is executed.Keys in the PKI are split into two halves, a public half and a private half. The public half ispublished and globally available, and the private half is kept secret and should be known onlyto the owner of that key. In the case of the code-signing PKI, the owners of code-signing keyswould be companies that produce device drivers, and Microsoft, the operating systemvendor. However, private keys are files that are stored on general purpose computers. Technologyexists to protect private keys by storing them within high security modules whoseonly purpose is protecting cryptographic keys. However, the infrastructure that is used toproduce signed device drivers is not compatible with the high security module infrastructure.In such an environment, companies also have to work with their private keys practically.Microsoft provides a mechanism to place Windows into “test signing” mode, so that devicedrivers that are not signed with a globally recognized key may still be loaded. However, “testsigning” mode is cumbersome and requires, effectively, the maintenance of a secondary PKIwithin the company writing device drivers. Additionally, the threat of theft of a code-signingprivate key, until recently, has been seen as both remote and abstract. The code-signing keyshad little value and, apparently, no organization was attempting their mass compromise. 5It is not generally known how the Duqu and Stuxnet authors obtained the code-signingcertificates to sign their device drivers. All that is known is that stolen certificates in Stuxnetwere from Realtek Semiconductor Corp. and JMicron Technology Corp., 6 while the Duqu certificateswere stolen from C-Media Electronics, Inc. 7 It can be assumed that these companieswere not complicit in the development of malicious software. Therefore, the best explanationfor the use of the code-signing certificates is that they were stolen. It is notable that bothRealtek and JMicron have offices in Hsinchu Science Park, Taiwan. 8 Hence, the geographicproximity may suggest physical theft in the case of Stuxnet. Further, C-Media is also aTaiwanese company. 9This is not wholly remarkable. The theft of private keys has always been a problem withdeployments of PKI. For this reason, high-security modules were developed that could betrusted with holding private keys. These high-security modules have memory to store theprivate key and processors to interact with data and the private key, but they do not allowthe transfer of the private key off of the high-security module. Using this technology, theftof a private key is only possible by the theft of the physical module.