Cryptographic Protocols & Ciphers

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Abstractions about securing information through cryptographic and authentication schemes — classical ciphers like the Caesar and transposition ciphers and frequency analysis, quantum key-distribution protocols such as BB84, B92, and the six-state protocol, and hardness assumptions and authentication models like multi-factor and passwordless authentication.

15 abstractions in this family — domain-specific abstractions that sit near one another in structural-signature space (k-means over structural-signature embeddings). Each is shown with its short description.

• Anonymous P2P — A peer-to-peer architecture designed to hide or minimize linkability between participants and their network locations.
• B92 protocol — A two-state quantum key-distribution protocol whose security relies on the impossibility of perfectly distinguishing nonorthogonal quantum states without disturbance.
• BB84 — A quantum key-distribution protocol in which randomly chosen conjugate encoding bases let two parties sift correlated bits and estimate whether interception disturbed the channel before deriving a shorter secret key.
• Biba Model — A mandatory access-control integrity model that orders subjects and objects by integrity level and restricts information flow to prevent lower-integrity data from contaminating higher-integrity state.
• Caesar cipher — A monoalphabetic substitution cipher replacing each symbol with the symbol a fixed offset away in a cyclic alphabet.
• Decisional Diffie–Hellman assumption — The cryptographic hardness assumption that a genuine Diffie–Hellman tuple is computationally indistinguishable from one with an independent random final group element.
• Frequency analysis — Cryptanalysis that exploits nonuniform symbol or pattern frequencies in ciphertext to infer a substitution or other weak classical encoding.
• Multi-factor authentication — Authentication requiring evidence from at least two independent factor categories such as knowledge, possession, and inherence before granting access.
• Nothing-up-my-sleeve number — A cryptographic constant selected by a simple publicly verifiable procedure with little discretionary freedom, reducing suspicion that hidden properties or a backdoor were chosen deliberately.
• Passwordless authentication — Authentication that verifies a claimant without requiring entry of a memorized knowledge secret, usually through a registered device, cryptographic key or inherence factor.
• Quantum digital signature — A signature protocol using quantum-state distribution and measurement properties to provide message authentication, transferability and resistance to repudiation or forgery.
• Quantum key distribution — A cryptographic key-establishment method that encodes and measures quantum states so eavesdropping creates detectable disturbance, followed by authenticated classical reconciliation and privacy amplification.
• Six-state protocol — Distribute quantum-key bits by randomly preparing and measuring qubits in three mutually unbiased bases, then sift, estimate errors, reconcile, and privacy-amplify the retained data.
• Symmetric-Key Cipher — Symmetric-key algorithms are algorithms for cryptography that use the same cryptographic keys for both the encryption of plaintext and the decryption of ciphertext.
• Transposition cipher — A classical cipher that permutes plaintext symbol positions according to a key while preserving the symbol multiset, unlike substitution which changes symbol identities.