Читать книгу Security Engineering - Ross Anderson - Страница 199

Very few attacks on systems nowadays involve cryptanalysis in the sense of a mathematical attack on the encryption algorithm or key. There have indeed been attacks on systems designed in the 20th century, mostly involving keys that were kept too short by export-control rules, clueless designs or both. I already discussed in section 4.3.1 how weak crypto has facilitated a wave of car theft, as all the devices used for remote key entry were defeated one after another in 2005–15. In later chapters, I give examples of how the crypto wars and their export control rules resulted in attacks on door locks (section 13.2.5), mobile phones (section 22.3.1) and copyright enforcement (section 24.2.5).

Most attacks nowadays exploit the implementation. In chapter 2, I mentioned the scandal of NIST standardising a complicated random number generator based on elliptic curves that turned out to contain an NSA backdoor; see section 2.2.1.5. Poor random number generators have led to many other failures: RSA keys with common factors [1142], predictable seeds for discrete logs [1679], etc. These vulnerabilities have continued; thanks to the Internet of Things, the proportion of RSA certs one can find out there on the Internet that share a common factor with other RSA keys has actually risen between 2012 and 2020; 1 in 172 IoT certs are trivially vulnerable [1048].

Many of the practical attacks on cryptographic implementations that have forced significant changes over the past 20 years have exploited side channels such as timing and power analysis; I devote Chapter 19 to these.

In Chapter 20, I'll discuss a number of systems that use public-key mechanisms in intricate ways to get interesting emergent properties, including the Signal messaging protocol, the TOR anonymity system, and cryptocurrencies. I'll also look at the crypto aspects of SGX enclaves. These also have interesting failure modes, some but not all of them relating to side channels.

In Chapter 21, I'll discuss protocols used in network infrastructure such as DKIM, DNSSec versus DNS over HTTP, and SSH.