(…) the NSA cryptologists divided their targets into five levels corresponding to the degree of the difficulty of the attack and the outcome, ranging from "trivial" to "catastrophic."
Monitoring a document's path through the Internet is classified as "trivial." Recording Facebook chats is considered a "minor" task, while the level of difficulty involved in decrypting emails sent through Moscow-based Internet service provider "mail.ru" is considered "moderate." Still, all three of those classifications don't appear to pose any significant problems for the NSA.
Things first become troublesome at the fourth level. The presentation states that the NSA encounters "major" problems in its attempts to decrypt messages sent through heavily encrypted email service providers like Zoho or in monitoring users of the Tor network*, which was developed for surfing the web anonymously. Tor, otherwise known as The Onion Router, is free and open source software that allows users to surf the web through a network of more than 6,000 linked volunteer computers. The software automatically encrypts data in a way that ensures that no single computer in the network has all of a user's information. For surveillance experts, it becomes very difficult to trace the whereabouts of a person who visits a particular website or to attack a specific person while they are using Tor to surf the Web.
The NSA also has "major" problems with Truecrypt, a program for encrypting files on computers. Truecrypt's developers stopped their work on the program last May, prompting speculation about pressures from government agencies. A protocol called Off-the-Record (OTR) for encrypting instant messaging in an end-to-end encryption process also seems to cause the NSA major problems. Both are programs whose source code can be viewed, modified, shared and used by anyone. Experts agree it is far more difficult for intelligence agencies to manipulate open source software programs than many of the closed systems developed by companies like Apple and Microsoft. Since anyone can view free and open source software, it becomes difficult to insert secret back doors without it being noticed. Transcripts of intercepted chats using OTR encryption handed over to the intelligence agency by a partner in Prism -- an NSA program that accesses data from at least nine American internet companies such as Google, Facebook and Apple -- show that the NSA's efforts appear to have been thwarted in these cases: "No decrypt available for this OTR message." This shows that OTR at least sometimes makes communications impossible to read for the NSA.
Things become "catastrophic" for the NSA at level five - when, for example, a subject uses a combination of Tor, another anonymization service, the instant messaging system CSpace and a system for Internet telephony (voice over IP) called ZRTP. This type of combination results in a "near-total loss/lack of insight to target communications, presence," the NSA document states.
ZRTP, which is used to securely encrypt conversations and text chats on mobile phones, is used in free and open source programs like RedPhone and Signal. "It's satisfying to know that the NSA considers encrypted communication from our apps to be truly opaque," says RedPhone developer Moxie Marlinspike.
VPN connections can be based on a number of different protocols. The most widely used ones are called Point-to-Point Tunneling Protocol (PPTP) and Internet Protocol Security (Ipsec). Both seem to pose few problems for the NSA spies if they really want to crack a connection. Experts have considered PPTP insecure for some time now, but it is still in use in many commercial systems. (…) Ipsec as a protocol seems to create slightly more trouble for the spies. But the NSA has the resources to actively attack routers involved in the communication process to get to the keys to unlock the encryption rather than trying to break it, courtesy of the unit called Tailored Access Operations: "TAO got on the router through which banking traffic of interest flows," it says in one presentation.
Even more vulnerable than VPN systems are the supposedly secure connections ordinary Internet users must rely on all the time for Web applications like financial services, e-commerce or accessing webmail accounts. A lay user can recognize these allegedly secure connections by looking at the address bar in his or her Web browser: With these connections, the first letters of the address there are not just http -- for Hypertext Transfer Protocol -- but https. The "s" stands for "secure". The problem is that there isn't really anything secure about them. (…) The NSA and its allies routinely intercept such connections -- by the millions. According to an NSA document, the agency intended to crack 10 million intercepted https connections a day by late 2012. (…)
The NSA also has a program with which it claims it can sometimes decrypt the Secure Shell protocol (SSH). This is typically used by systems administrators to log into employees' computers remotely, largely for use in the infrastructure of businesses, core Internet routers and other similarly important systems. The NSA combines the data collected in this manner with other information to leverage access to important systems of interest.