Security Engineering. Ross Anderson

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СКАЧАТЬ find suspects and identify strong selectors (such as email addresses, phone numbers or IP addresses) for more conventional collection.

      Xkeyscore is a federated system, where one query scans all sites. Its components buffer information at collection points – in 2008, 700 servers at 150 sites. Some appear to be hacked systems overseas from which the NSA malware can exfiltrate data matching a submitted query. The only judicial approval required is a prompt for the analyst to enter a reason why they believe that one of the parties to the conversation is not resident in the USA. The volumes are such that traffic data are kept for 30 days but content for only 3–5 days. Tasked items are extracted and sent on to whoever requested them, and there's a notification system (Trafficthief) for tipping off analysts when their targets do anything of interest. Extraction is based either on fingerprints or plugins – the latter allow analysts to respond quickly with detectors for new challenges like steganography and homebrew encryption.

      Xkeyscore can also be used for target discovery: one of the training queries is “Show me all the exploitable machines in country X” (machine fingerprints are compiled by a crawler called Mugshot). For example, it came out in 2015 that GCHQ and the NSA hacked the world's leading provider of SIM cards, the Franco-Dutch company Gemalto, to compromise the keys needed to intercept (and if need be spoof) the traffic from hundreds of millions of mobile phones [1661]. The hack used Xkeyscore to identify the firm's sysadmins, who were then phished; agents were also able to compromise billing servers to suppress SMS billing and authentication servers to steal keys; another technique was to harvest keys in transit from Gemalto to mobile service providers. According to an interview with Snowden in 2014, Xkeyscore also lets an analyst build a fingerprint of any target's online activity so that they can be followed automatically round the world. The successes of this system are claimed to include the capture of over 300 terrorists; in one case, Al-Qaida's Sheikh Atiyatallah blew his cover by googling himself, his various aliases, an associate and the name of his book [1661].

      There's a collection of decks on Xkeyscore with a survey by Morgan Marquis-Boire, Glenn Greenwald and Micah Lee [1232]; a careful reading of the decks can be a good starting point for exploring the Snowden hoard⁴.

       2.2.1.7 Longhaul

      Bulk key theft and supply-chain tampering are not the only ways to defeat cryptography. The Xkeyscore training deck gives an example: “Show me all the VPN startups in country X, and give me the data so I can decrypt and discover the users”. VPNs appear to be easily defeated; a decryption service called Longhaul ingests ciphertext and returns plaintext. The detailed description of cryptanalytic techniques is held as Extremely Compartmented Information (ECI) and is not found in the Snowden papers, but some of them talk of recent breakthroughs in cryptanalysis. What might these be?

      The leaks do show diligent collection of the protocol messages used to set up VPN encryption, so some cryptographers suggested in 2015 that some variant of the “Logjam attack” is feasible for a nation-state attacker against the 1024-bit prime used by most VPNs and many TLS connections with Diffie-Hellman key exchange [26]. Others pointed to the involvement of NSA cryptographers in the relevant standard, and a protocol flaw discovered later; yet others pointed out that even with advances in number theory or protocol exploits, the NSA has enough money to simply break 1024-bit Diffie-Hellman by brute force, and this would be easily justified if many people used the same small number of prime moduli – which they do [854]. I'll discuss cryptanalysis in more detail in Chapter 5.

       2.2.1.8 Quantum

      There is a long history of attacks on protocols, which can be spoofed, replayed and manipulated in various ways. (We'll discuss this topic in detail in Chapter 4.) The best-documented NSA attack on Internet traffic goes under the codename of Quantum and involves the dynamic exploitation of one of the communication end-points. Thus, to tap an encrypted SSL/TLS session to a webmail provider, the Quantum system fires a ‘shot’ that exploits the browser. There are various flavours; in ‘Quantuminsert’, an injected packet redirects the browser to a ‘Foxacid’ attack server. Other variants attack software updates and the advertising networks whose code runs in mobile phone apps [1999].

2.2.1.9 CNE

Computer and Network Exploitation (CNE) is the generic NSA term for hacking, and it can be used for more than just key theft or TLS session hijacking; it can be used to acquire access to traffic too. Operation Socialist was the GCHQ codename for a hack of Belgium's main telco Belgacom⁵ in 2010–11. GCHQ attackers used Xkeyscore to identify three key Belgacom technical staff, then used Quantuminsert to take over their PCs when they visited sites like LinkedIn. The attackers then used their sysadmin privileges to install malware on dozens of servers, including authentication servers to leverage further access, billing servers so they could cover their tracks, and the company's core Cisco routers [734]. This gave them access to large quantities of mobile roaming traffic, as Belgacom provides service to many foreign providers when their subscribers roam in Europe. The idea that one NATO and EU member state would conduct a cyber-attack on the critical infrastructure of another took many by surprise. The attack also gave GCHQ access to the phone system in the European Commission and other European institutions. Given that these institutions make many of the laws for the UK and other member states, this was almost as if a US state governor had got his state troopers to hack AT&T so he could wiretap Congress and the White House.

      Belgacom engineers started to suspect something was wrong in 2012, and realised they'd been hacked in the spring of 2013; an anti-virus company found sophisticated malware masquerading as Windows files. The story went public in September 2013, and the German news magazine Der Spiegel published Snowden documents showing that GCHQ was responsible. After the Belgian prosecutor reported in February 2018, we learned that the attack must have been authorised by then UK Foreign Secretary William Hague, but there was not enough evidence to prosecute anyone; the investigation had been hampered in all sorts of ways both technical and political; the software started deleting itself within minutes of discovery, and institutions such as Europol (whose head was British) refused to help. The Belgian minister responsible for telecomms, Alexander de Croo, even suggested that Belgium's own intelligence service might have informally given the operation a green light [735]. Europol later adopted a policy that it will help investigate hacks of ‘suspected criminal origin’; it has nothing to say about hacks by governments.

      A GCHQ slide deck on CNE explains that it's used to support conventional Sigint both by redirecting traffic and by “enabling” (breaking) cryptography; that it must always be “UK deniable”; and that it can also be used for “effects”, such as degrading communications or “changing users' passwords on extremist website” [735]. Other papers show that the agencies frequently target admins of phone companies and ISPs in the Middle East, Africa and indeed worldwide – compromising a key technician is “generally the entry ticket to the network” [1141]. As one phone company executive explained, “The MNOs were clueless at the time about network security. Most networks were open to their suppliers for remote maintenance with an ID and password and the techie in China or India had no clue that their PC had been hacked”.

      The hacking tools and methods used by the NSA and its allies are now fairly well understood; some are shared with law enforcement. The Snowden papers reveal an internal store where analysts can get a variety of tools; a series of leaks in 2016–7 by the Shadow Brokers (thought to be Russian military intelligence, the GRU) disclosed a number of actual NSA malware samples, used by hackers at the NSA's Tailored Access Operations team to launch attacks [239]. (Some of these tools were repurposed by the Russians to launch the NotPetya worm and by the North Koreans in Wannacry, as I'll discuss later.) The best documentation of all is probably about a separate store of goodies used by the СКАЧАТЬ