Cryptographic backdoor

A cryptographic backdoor is a deliberate vulnerability inserted into an encryption system that allows an authorized party — typically a government or intelligence agency — to bypass the system's security guarantees while the system remains secure against all other adversaries. The concept became central to the cryptography wars of the 1990s and 2010s, when governments proposed key escrow systems requiring manufacturers to build in lawful access mechanisms. The structural problem, articulated by Martin Hellman and others, is that a backdoor for legitimate access is mathematically indistinguishable from a vulnerability to malicious exploitation: the mathematics does not know the intent of the user. Any system with a backdoor is a system that is not secure, regardless of who holds the key.