February 05, 2026 -- While the current digital world relies on a few fundamental building blocks known as cryptographic primitives, many of these are threatened by the potential rise of large-scale quantum computers. To address this, researchers are developing quantum cryptography, a discipline that uses the fundamental laws of physics to provide security levels that are often impossible to achieve with classical resources. While quantum key distribution (QKD) is the most mature of these technologies, in this recent publication, QSNP researchers from the University of Vienna illustrate a massive landscape of “beyond-QKD” primitives that are essential for the future of secure communication and computation.

The foundation of these protocols’ security lies in quantum tools such as conjugate coding and the no-cloning theorem. Conjugate coding, originally proposed by Stephen Wiesner, leverages the uncertainty principle to encode information in a way that measuring one property of a quantum system inherently disturbs another. This means a hacker trying to intercept information without knowing the correct “basis” will alter the state, a change that honest parties can detect. Complementing this is the no-cloning theorem, which states that it is physically impossible to create an identical copy of an unknown quantum state without introducing noise. These principles provide the backbone for quantum advantage, allowing for security that relies on quantum theory rather than just the difficulty of solving a math problem.

One major branch of this field is trustful quantum cryptography, in which at least one participant in the communication is honest. A pioneering application here is unforgeable tokens, or quantum money, which uses the no-cloning theorem to create banknotes that are physically impossible to duplicate. In this scenario, a bank encodes secret keys into qubits. Since an attacker cannot perfectly copy the state of these qubits, any attempt to produce a second valid note for “double spending” would be detected during verification. Other applications include unclonable encryption, where any attempt by an eavesdropper to copy a ciphertext for later decryption is fundamentally detectable, and covert communication, which aims to hide the very existence of a message from unauthorized parties. Examples relating to non-digital credentials also exist: in quantum position verification for instance, one party can verify that a given message originates from a specific geographical position (such as a trusted ally military base).

When the participants themselves don’t trust each other, we enter the realm of mistrustful quantum cryptography. This area covers tasks like digital signatures, which verify the authenticity of a message, and bit commitment, a process often compared to putting a bit in a “locked safe” to be revealed later. Although “no-go” theorems have proven that perfect, information-theoretically secure bit commitment and oblivious transfer (where a receiver gets only one of two messages without the sender knowing which) are impossible with quantum resources alone, they can still be achieved by accepting a small, finite cheating probability. Furthermore, these limitations can be avoided by introducing additional physical assumptions, such as special relativity. Relativistic protocols use no-signaling constraints to ensure that a dishonest party cannot cheat by delaying their quantum measurements in time.

As we move toward global quantum networks, multipartite primitives become necessary to coordinate many users simultaneously. Secret sharing allows a central authority to divide a secret among a group so that it can only be retrieved if a specific subset of them collaborates. This is vital for high-stakes scenarios, such as the distributed storage of cryptographic keys. Other network-level tasks include Byzantine agreement, which allows a system of processors to reach a consensus even if some are acting as traitors, and randomized leader election, which picks a “leader” among a group of potentially dishonest participants. These networks also require anonymous communication protocols, which protect the identity of the sender or receiver of a message, ensuring that the act of communicating does not reveal who is involved.

In their review, the QSNP researchers also explore secure quantum computation, which focuses on delegating tasks to powerful but untrusted servers. Blind quantum computation allows the clients with very limited hardware to run a program on a remote server while keeping their input, the program’s nature, and the final output completely hidden from that server. To ensure the server actually implemented the correct algorithm, verifiable computation incorporates “traps”, qubits with predetermined outcomes known only to the client, that allow the client to check the server’s integrity. While early versions required the client to have some quantum capabilities, newer research into fully homomorphic encryption and classical-client protocols aims to allow users with entirely classical devices to verify the work of a quantum cloud server.

In summary, this review represents a meaningful step towards making quantum cryptography beyond QKD understandable for a broader community. By offering an intuitive classification of quantum-cryptographic primitives, outlining the current capabilities and limitations the article helps bridge the gap between theory and experiment.

Looking ahead, progress will depend on identifying concrete use cases, developing noise and loss-tolerant security proofs, and matching quantum primitives with the most suitable hardware platforms. By lowering the entry barrier to this field, this work aims to empower the next generation of researchers to contribute to the development of secure quantum networks and to shape the future of quantum communications.