Cryptography Cheat Sheet

The core ideas of Cryptography distilled into a single, scannable reference — perfect for review or quick lookup.

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Quick Reference

Symmetric-Key Encryption

An encryption scheme where the same secret key is used for both encryption and decryption. Both the sender and receiver must possess the identical key, which must be kept secret from all other parties.

Public-Key (Asymmetric) Cryptography

A cryptographic system that uses a pair of mathematically related keys: a public key that can be freely shared for encryption, and a private key kept secret for decryption. It solves the key distribution problem inherent in symmetric cryptography.

Hash Functions

One-way mathematical functions that take an input of any size and produce a fixed-size output (digest) that is computationally infeasible to reverse. Even a tiny change in input produces a completely different hash, a property called the avalanche effect.

Digital Signatures

A cryptographic mechanism that allows the signer to prove the authenticity and integrity of a message. The sender signs with their private key, and anyone can verify the signature using the sender's public key, providing authentication and non-repudiation.

Key Exchange Protocols

Methods that allow two parties to establish a shared secret key over an insecure channel without any prior shared secret. The Diffie-Hellman protocol was the first practical solution to this fundamental problem.

Block Ciphers vs. Stream Ciphers

Block ciphers encrypt fixed-size blocks of plaintext (e.g., 128 bits for AES), while stream ciphers encrypt data one bit or byte at a time using a pseudorandom keystream. Each has different performance characteristics and use cases.

Cryptanalysis

The study of methods for obtaining the meaning of encrypted information without access to the secret key. It encompasses techniques ranging from brute-force attacks to sophisticated mathematical analysis exploiting weaknesses in cryptographic algorithms.

Public Key Infrastructure (PKI)

A framework of policies, hardware, software, and procedures used to create, manage, distribute, store, and revoke digital certificates. PKI establishes a chain of trust that binds public keys to the identities of their owners.

Zero-Knowledge Proofs

A cryptographic method by which one party (the prover) can prove to another party (the verifier) that a given statement is true without revealing any information beyond the validity of the statement itself.

Post-Quantum Cryptography

Cryptographic algorithms designed to be secure against attacks by both classical and quantum computers. These algorithms rely on mathematical problems believed to be hard even for quantum computers, such as lattice-based and hash-based problems.

Key Terms at a Glance

AES:Advanced Encryption Standard; a symmetric block cipher with 128-bit blocks and key sizes of 128, 192, or 256 bits.

Asymmetric Encryption:Encryption using a pair of keys: one public for encryption, one private for decryption.

Authentication:The process of verifying the identity of a user, device, or other entity in a communication.

Avalanche Effect:A property of cryptographic algorithms where a small change in input causes a significant change in output.

Block Cipher:A symmetric cipher that encrypts data in fixed-size blocks using a secret key.

Certificate Authority:A trusted entity that issues digital certificates binding public keys to verified identities.

Cipher:An algorithm for performing encryption or decryption, transforming plaintext into ciphertext and vice versa.

Ciphertext:The encrypted, unreadable form of a message produced by applying an encryption algorithm.

Collision Resistance:The property of a hash function that makes it computationally infeasible to find two different inputs that produce the same output.

Cryptanalysis:The study of methods for breaking cryptographic systems and obtaining encrypted information without the key.

Decryption:The process of converting ciphertext back into readable plaintext using a key or algorithm.

Digital Certificate:An electronic document that uses a digital signature to bind a public key with an identity.

Diffie-Hellman:A key exchange protocol allowing two parties to establish a shared secret over an insecure channel.

Elliptic Curve Cryptography:Public-key cryptography based on elliptic curves, offering strong security with smaller key sizes than RSA.

Encryption:The process of converting readable plaintext into unreadable ciphertext to protect its confidentiality.

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