Many activities require secure electronic communications. To facilitate secure electronic communications, an encryption/decryption system may be implemented on an electronic assembly or printed circuit board assembly that is included in equipment connected to a communications network. Such an electronic assembly is an enticing target for malefactors since it may contain codes or keys to decrypt intercepted messages, or to encode fraudulent messages. To prevent this, an electronic assembly may be mounted in an enclosure, which is then wrapped in a security sensor and encapsulated with polyurethane resin. A security sensor may be, in one or more embodiments, a web or sheet of insulating material with circuit elements, such as closely-spaced, conductive lines fabricated on it. The circuit elements are disrupted if the sensor is torn, and the tear can be sensed in order to generate an alarm signal. The alarm signal may be conveyed to a monitor circuit in order to reveal an attack on the integrity of the assembly. The alarm signal may also trigger an erasure of encryption/decryption keys stored within the electronic assembly.