Post-Quantum Cryptography: IT Security in the Era of Quantum Technology

A quantum computer is a new type of computer that is clearly superior to the classic PC in terms of some problems. Instead of bits, a quantum computer works with qubits.

Qubits are the quantum computer equivalent of the classical bit. A bit can only store information as either “0” or “1”, but a qubit can also be in an intermediate state.

• Asymmetric Cryptography: cryptography using two distinct keys, a private one (restricted to the key's owner) and an associated public key (known to everyone); each pair of public and private key can be used for an operation and its counterpart (e.g. encryption with public key, decryption with private key; signature generation with private key, signature validation with public key); can be used to communicate via untrusted channels without prior exchange of keys

• Classical Cryptography: if used in context of post-quantum cryptography: mainly referring to asymmetric algorithms which are not secure against attacks with a quantum computer, e.g. RSA, ECC, DH, ECDSA

• Key Exchange: computation of a shared secret by several parties in a protocol run; exchanged messages do not require confidentiality (but authenticity) to keep computed secret confidential

• Post-Quantum Cryptography: cryptography, which can be used on classical computers and which is secure against both classical attacks as well as known attacks with quantum computer; uses different mathematical problems than classical cryptography; does not require a quantum computer

• Superposition: property of quantum object to reside in a state between two basis states (e.g. 0 and 1); in contrast to common intuition, where objects are “either-or”: either here or there, either one or zero, etc.; in quantum physics (physics of small particles) this is not the case, but particles can be in an intermediate state

• Symmetric Cryptography: cryptography using the same (pre-shared) key for an operation and its counterpart (e.g. encryption/decryption; creation/validation of a message authentication code); requires secure sharing of this key prior to first use

• Quantum Computer: new kind of computing device highly superior to classical computers for specific tasks; instead of bits, quantum computers use qubits

• Quantum Computing: computation using a quantum computer

• Quantum Cryptography: cryptography using quantum physics with new hardware and new protocols

• Entanglement: combination of several quantum objects acting as one entity; any change on one of these objects results in a simultaneous change of all entangled partners

• Quantum Key Distribution: secure distribution of key material using quantum physical effects; currently still slow and with limited range between partners

• Qubit: the quantum computer’s analogon to the classical bit; while a bit stores information as either a “0” or a “1”, a qubit can also reside in an intermediate state between 0 and 1

There are different assumptions in research as to when the first commercial quantum computers will be available. Some experts assume that quantum computers could be able to break cryptographic procedures in the next 10 to 20 years. Others estimate that this could take longer.

Yes, as post-quantum cryptography also works on conventional computers, no quantum computer is required to develop, implement or use PQC. Companies can therefore start the transition at an early stage.