In cryptography, black-bag cryptanalysis is a euphemism for the acquisition of cryptographic secrets via burglary, or other covert means – rather than mathematical or technical cryptanalytic attack.
Regardless of the technique used, such methods are intended to capture highly sensitive information e.g. cryptographic keys, key-rings, passwords or unencrypted plaintext.
The required information is usually copied without removing or destroying it, so capture often takes place without the victim realizing it has occurred.
[4] Although sophisticated technology is often used, black bag cryptanalysis can also be as simple as the process of copying a password which someone has unwisely written down on a piece of paper and left inside their desk drawer.
The case of United States v. Scarfo highlighted one instance in which FBI agents using a sneak and peek warrant placed a keystroke logger on an alleged criminal gang leader.