Backdoor (computing)
A backdoor is a typically covert method of bypassing normal authentication or encryption in a computer, product, embedded device (e.g. a home router), or its embodiment (e.g. part of a cryptosystem, algorithm, chipset, or even a "homunculus computer"—a tiny computer-within-a-computer such as that found in Intel's AMT technology).
[14] In 1993, the United States government attempted to deploy an encryption system, the Clipper chip, with an explicit backdoor for law enforcement and national security access.
[17] They noted a class of active infiltration attacks that use "trapdoor" entry points into the system to bypass security facilities and permit direct access to data.
More generally, such security breaches were discussed at length in a RAND Corporation task force report published under DARPA sponsorship by J.P. Anderson and D.J.
Programmers have even succeeded in secretly installing large amounts of benign code as Easter eggs in programs, although such cases may involve official forbearance, if not actual permission.
In some cases, these might begin life as an actual bug (inadvertent error), which, once discovered are then deliberately left unfixed and undisclosed, whether by a rogue employee for personal advantage, or with executive awareness and oversight.
[note 1] In general terms, the long dependency-chains in the modern, highly specialized technological economy and innumerable human-elements process control-points make it difficult to conclusively pinpoint responsibility at such time as a covert backdoor becomes unveiled.
Others, such as the Sony/BMG rootkit, placed secretly on millions of music CDs through late 2005, are intended as DRM measures—and, in that case, as data-gathering agents, since both surreptitious programs they installed routinely contacted central servers.
A sophisticated attempt to plant a backdoor in the Linux kernel, exposed in November 2003, added a small and subtle code change by subverting the revision control system.
The Samsung proprietary Android versions are fitted with a backdoor that provides remote access to the data stored on the device.
In particular, the Samsung Android software that is in charge of handling the communications with the modem, using the Samsung IPC protocol, implements a class of requests known as remote file server (RFS) commands, that allows the backdoor operator to perform via modem remote I/O operations on the device hard disk or other storage.
As the modem is running Samsung proprietary Android software, it is likely that it offers over-the-air remote control that could then be used to issue the RFS commands and thus to access the file system on the device.
Thus for such backdoors to avoid detection, all extant copies of a binary must be subverted, and any validation checksums must also be compromised, and source must be unavailable, to prevent recompilation.
The notion of an asymmetric backdoor was introduced by Adam Young and Moti Yung in the Proceedings of Advances in Cryptology – Crypto '96.
This OpenSSL RSA backdoor, designed by Young and Yung, utilizes a twisted pair of elliptic curves, and has been made available.
Karger and Schell gave an updated analysis of the original exploit in 2002, and, in 2009, Wheeler wrote a historical overview and survey of the literature.
The virus introduced its own code to the compilation of new Delphi programs, allowing it to infect and propagate to many systems, without the knowledge of the software programmer.
The virus looks for a Delphi installation, modifies the SysConst.pas file, which is the source code of a part of the standard library and compiles it.
[note 5] In 2015, a malicious copy of Xcode, XcodeGhost, also performed a similar attack and infected iOS apps from a dozen of software companies in China.
It was not a true Thompson Trojan, as it does not infect development tools themselves, but it did prove that toolchain poisoning can cause substantial damages.
A formal proof is given that the latter comparison guarantees that the purported source code and executable of the compiler-under-test correspond, under some assumptions.
[30] In practice such verifications are not done by end users, except in extreme circumstances of intrusion detection and analysis, due to the rarity of such sophisticated attacks, and because programs are typically distributed in binary form.
