  Quantum computing is under rapid development, and today there are several
cloud-based, quantum computers (QCs) of modest size (>100s of physical qubits).
Although these QCs, along with their highly-specialized classical support
infrastructure, are in limited supply, they are readily available for remote
access and programming. This work shows the viability of using intrinsic
quantum hardware properties for fingerprinting cloud-based QCs that exist
today. We demonstrate the reliability of intrinsic fingerprinting with real QC
characterization data, as well as simulated QC data, and we detail a quantum
physically unclonable function (Q-PUF) scheme for secure key generation using
unique fingerprint data combined with fuzzy extraction. We use fixed-frequency
transmon qubits for prototyping our methods.
