Cryptography

Definition\n\nCryptography is the study and practice of techniques for secure communication in the presence of adversaries. It underpins blockchain security through two core tools: cryptographic hash functions and public-key cryptography.\n\n## Hash Functions\n\nHash functions map arbitrary data to fixed-length outputs that are fast to compute but practically impossible to invert. Changing any input changes the hash unpredictably, which makes them ideal for tamper detection and for linking blocks.\n\n## Public-Key Cryptography\n\nPublic-key cryptography uses a key pair: a public key for verification and a private key for signing. Users sign transactions with their private key, and anyone can verify the signature with the public key.\n\n## Role in Blockchain\n\nBlockchain networks depend on cryptography for data integrity (hashing), identity (digital signatures), and the Proof-of-Work puzzle itself.