Encryption Backdoor: What Is It & How Does It Work?

The Renewed Push for Backdoors in Encrypted Services

Discussions surrounding potential vulnerabilities in encrypted services have resurfaced following reports that the U.K. government is attempting to compel Apple to provide access to iCloud’s end-to-end encrypted (E2EE) device backup functionality. It is alleged that officials are pressuring Apple to engineer a “backdoor” within the service, enabling state actors to view data in an unencrypted format.

U.K. Surveillance Powers and Apple's Data Protection

Since the passage of a 2016 update to state surveillance legislation, the U.K. possesses extensive authority to restrict the implementation of robust encryption by technology companies. Reports in the Washington Post indicate that U.K. authorities are utilizing the Investigatory Powers Act (IPA) to demand this access from Apple – specifically, seeking “blanket” access to data protected by its iCloud Advanced Data Protection (ADP) service, even from Apple itself.

The ADP service’s technical design ensures that Apple does not possess the encryption keys, leveraging end-to-end encryption (E2EE) to guarantee “zero knowledge” of user data.

Understanding the Concept of a "Backdoor"

A “backdoor” generally refers to a deliberately introduced security flaw within code, designed to bypass security protocols and grant access to unauthorized third parties. In the context of iCloud, this order would allow U.K. intelligence or law enforcement to access users’ encrypted information.

While the U.K. government typically declines to confirm or deny reports of IPA-issued notices, security professionals caution that such a directive could have widespread consequences if Apple is forced to compromise the security safeguards offered to all users, regardless of location.

The Risks of Introducing Vulnerabilities

The creation of a vulnerability in software introduces the possibility of exploitation by malicious actors, such as hackers, who may seek to steal identities, acquire sensitive data, or deploy ransomware.

This explains why discussions surrounding state-sponsored attempts to access E2EE often employ the metaphor of a “backdoor”; explicitly requesting a vulnerability to be intentionally incorporated into code highlights the inherent trade-offs.

The Analogy of Physical Security

Consider a physical door: exclusive access is never guaranteed. Someone could duplicate a key or forcibly breach the door.

There is no perfectly selective access point; if entry is possible, others may also be able to utilize it.

This principle extends directly to vulnerabilities introduced into software or hardware.

The "NOBUS" Backdoor Concept

Security services have previously proposed the concept of “NOBUS” (“nobody but us”) backdoors, predicated on the belief that their technical capabilities for exploiting a vulnerability surpass those of all others – essentially a more secure backdoor accessible only to their agents.

However, technological prowess is constantly evolving, and accurately assessing the capabilities of unknown entities is challenging. The “NOBUS” concept relies on questionable assumptions, as any third-party access creates new attack vectors, including social engineering.

Consequently, many security experts dismiss NOBUS as fundamentally flawed, asserting that any access inherently creates risk, making the pursuit of backdoors counterproductive to strong security.

Secrecy and Legal Frameworks

The term “backdoor” also suggests a degree of secrecy, as these requests are often not made public – mirroring the non-public nature of backdoors themselves. Under the U.K.’s IPA, a request to compromise encryption via a “technical capability notice” (TCN) cannot be legally disclosed by the recipient.

The law intends for such backdoors to remain secret by design, although leaks to the press can circumvent this information block.

Historical Context of "Backdoors"

According to the Electronic Frontier Foundation, the term “backdoor” originated in the 1980s, referring to secret accounts or passwords granting unauthorized system access. Over time, it has encompassed a broader range of attempts to undermine encryption-enabled data security.

Data access demands are not new; in the 1990s, the U.S. National Security Agency (NSA) developed encrypted hardware, the “Clipper Chip,” with a built-in backdoor to allow interception of encrypted communications through key escrow.

The Failure of the Clipper Chip and the Rise of Strong Encryption

The NSA’s attempt to mandate the use of chips with built-in backdoors was unsuccessful due to security and privacy concerns. However, it spurred cryptographers to develop and disseminate strong encryption software to protect data from government surveillance.

The Clipper Chip demonstrates that backdoor attempts don’t always need to be covert.

Government Propaganda and Public Pressure

Governments often employ emotive language to garner public support for data access demands, framing them as necessary to combat issues like child abuse or terrorism.

The Risks of Backdoors: A Recent Example

Backdoors can have unintended consequences. China-backed hackers compromised federally mandated wiretap systems last fall, gaining access to U.S. telco and ISP user data due to a 30-year-old law requiring backdoor access to non-E2EE data.

Foreign Backdoors and National Security

Governments must also consider the risks posed by foreign backdoors to their own citizens and national security. Concerns about potential backdoors in Chinese hardware and software have led some countries, including the U.K., to restrict their use in critical infrastructure.