> What a future quantum computer would break, the new standards, and hybrid key exchange in TLS today. Chapters and guides in one place. Source: https://pkizerotohero.com/topics/post-quantum/ Topic # Post-quantum cryptography A large enough quantum computer would break the public-key algorithms in use today, such as RSA and elliptic-curve cryptography, while symmetric encryption such as AES is only weakened, not broken. Data recorded now could be decrypted later. New post-quantum algorithms are standardised, and hybrid key exchange already protects many TLS connections. This hub explains what changes, what to do now and how to test it. ## Understand it: handbook chapters Plain words first, then the real mechanism, what it looks like at work and why it matters. Chapter 26 ### [Post-quantum cryptography](https://pkizerotohero.com/handbook/post-quantum/) A large quantum computer would break RSA and elliptic-curve cryptography, so key exchange is already moving to ML-KEM, and signatures and certificates come next. - Expert - Leader - IT ops Chapter 4 ### [Key exchange and hybrid encryption](https://pkizerotohero.com/handbook/key-exchange/) Two parties can agree a shared secret over an open network without ever sending it, then derive fast symmetric keys from it to protect the actual data. - Developer - IT ops - Beginner Chapter 6 ### [Digital signatures](https://pkizerotohero.com/handbook/digital-signatures/) A digital signature is a value only the private-key holder can compute for a message, and anyone with the public key can check that it matches that exact, unchanged message. - Beginner - Developer - IT ops ## Do it: how-to guides Step-by-step, with real commands and a way to check it worked. ### [How to test post-quantum hybrid TLS](https://pkizerotohero.com/guides/post-quantum-tls-test/) You will know whether your servers and network negotiate the X25519MLKEM768 hybrid key exchange, and how to read, force and troubleshoot it with OpenSSL 3.5. - Linux - macOS - Windows ### [How to configure TLS securely (versions, ciphers, HSTS)](https://pkizerotohero.com/guides/tls-configuration/) You will have a web server that offers only TLS 1.2 and 1.3 with forward-secret ciphers, staples OCSP only where it still applies, sends HSTS safely, and passes testing. - nginx - Apache - Linux - Windows ## The big picture: crash course Short lessons of about nine minutes each, with check questions. - [Lesson 2: Two keys](https://pkizerotohero.com/course/two-keys/) - [Lesson 3: Fingerprints and signatures](https://pkizerotohero.com/course/fingerprints-and-signatures/) - [Lesson 10: Beyond the browser, and what comes next](https://pkizerotohero.com/course/beyond-the-browser/) ## Look it up: glossary terms Every term in plain words, linked to its full entry. - [Crypto-agility](https://pkizerotohero.com/handbook/glossary/#crypto-agility "The ability to replace cryptographic algorithms and keys quickly, without rebuilding the systems that use them.") - [Diffie-Hellman](https://pkizerotohero.com/handbook/glossary/#diffie-hellman "A method for two parties to agree a shared secret over a public channel, without ever sending the secret itself.") - [Digital signature](https://pkizerotohero.com/handbook/glossary/#digital-signature "A value computed from a message and a private key that anyone with the public key can check, proving who signed and that nothing changed.") - [ECDHE](https://pkizerotohero.com/handbook/glossary/#ecdhe "Elliptic-curve Diffie-Hellman Ephemeral: the usual key exchange in TLS 1.3, agreeing a fresh secret for every connection.") - [ECDSA](https://pkizerotohero.com/handbook/glossary/#ecdsa "The Elliptic Curve Digital Signature Algorithm, widely used in TLS certificates, often on the P-256 curve.") - [Grover's algorithm](https://pkizerotohero.com/handbook/glossary/#grovers-algorithm "A quantum algorithm that speeds up brute-force search, roughly halving the effective strength of symmetric keys and hashes.") - [Harvest now, decrypt later](https://pkizerotohero.com/handbook/glossary/#harvest-now-decrypt-later "Recording encrypted traffic today in the hope of decrypting it once a large quantum computer can break the key exchange.") - [Hybrid encryption](https://pkizerotohero.com/handbook/glossary/#hybrid-encryption "Using public-key cryptography to agree or protect a symmetric key, and that fast symmetric key to encrypt the actual data.") - [Hybrid key exchange](https://pkizerotohero.com/handbook/glossary/#hybrid-key-exchange "Running a classical and a post-quantum key exchange together and combining both secrets, so the result is safe if either one holds.") - [Key encapsulation mechanism (KEM)](https://pkizerotohero.com/handbook/glossary/#key-encapsulation-mechanism "A way to agree a shared secret: one side encapsulates a fresh secret to a public key, and only the private key recovers it.") - [Key exchange](https://pkizerotohero.com/handbook/glossary/#key-exchange "A protocol by which two parties agree a shared secret over an open network, so they can then use fast symmetric encryption.") - [ML-DSA](https://pkizerotohero.com/handbook/glossary/#ml-dsa "Module-Lattice-Based Digital Signature Algorithm: a post-quantum signature standard (FIPS 204), derived from CRYSTALS-Dilithium.") - [ML-KEM](https://pkizerotohero.com/handbook/glossary/#ml-kem "Module-Lattice-Based Key-Encapsulation Mechanism: the post-quantum key agreement standard (FIPS 203), derived from CRYSTALS-Kyber.") - [Post-quantum cryptography (PQC)](https://pkizerotohero.com/handbook/glossary/#post-quantum-cryptography "Public-key algorithms designed to stay secure even against large quantum computers, running on ordinary hardware.") - [Session key](https://pkizerotohero.com/handbook/glossary/#session-key "A symmetric key that protects one connection or session, then is thrown away.") - [Shor's algorithm](https://pkizerotohero.com/handbook/glossary/#shors-algorithm "A quantum algorithm that could factor large numbers and compute discrete logarithms, breaking RSA and elliptic-curve cryptography.") - [SLH-DSA](https://pkizerotohero.com/handbook/glossary/#slh-dsa "Stateless Hash-Based Digital Signature Algorithm: a post-quantum signature standard (FIPS 205) whose security rests only on hash functions.") - [X25519](https://pkizerotohero.com/handbook/glossary/#x25519 "A fast, widely used elliptic-curve Diffie-Hellman function on Curve25519, the default key exchange in most TLS 1.3 connections.") ## Other topics - [Certificates](https://pkizerotohero.com/topics/certificates/) - [Chains and trust stores](https://pkizerotohero.com/topics/chains-and-trust/) - [TLS and HTTPS](https://pkizerotohero.com/topics/tls/) - [Lifecycle and automation](https://pkizerotohero.com/topics/lifecycle-and-automation/) - [Revocation and transparency](https://pkizerotohero.com/topics/revocation-and-transparency/) - [Private PKI](https://pkizerotohero.com/topics/private-pki/) - [Hashes and signatures](https://pkizerotohero.com/topics/signing/)