/ˈkrɪp.təˌɡræ.fi/
noun — "the art and science of keeping information secret and verifiable."
Cryptography is the study and practice of techniques for securing communication and data from unauthorized access, manipulation, or interception. It involves transforming readable data (plaintext) into an encoded form (ciphertext) using mathematical algorithms and keys, ensuring confidentiality, integrity, authentication, and non-repudiation. Cryptography underpins secure digital communication, online banking, blockchain systems, and password protection.
Technically, cryptography encompasses symmetric-key methods, where the same key is used for encryption and decryption, and asymmetric-key methods (public-key cryptography), where a public key encrypts data and a private key decrypts it. Hash functions create fixed-length digests to verify data integrity without revealing the original content. Modern cryptography also includes digital signatures, zero-knowledge proofs, and authenticated encryption schemes for secure protocols like TLS/SSL and VPNs.
Key characteristics of cryptography include:
- Confidentiality: prevents unauthorized parties from reading sensitive data.
- Integrity: ensures data has not been altered during transmission.
- Authentication: verifies the identity of communicating parties.
- Non-repudiation: prevents senders from denying actions, often via digital signatures.
- Algorithm-driven: relies on mathematical functions, keys, and protocols to secure data.
In practical workflows, cryptography is implemented in secure messaging, online payments, data storage, and network protocols. For example, a secure website uses asymmetric cryptography to exchange a session key, which then enables symmetric encryption for faster communication. Engineers also apply hashing algorithms like SHA-256 to verify file integrity and use digital certificates to validate identity in public-key infrastructures (PKI).
Conceptually, cryptography is like sealing a message in a locked, uniquely keyed box: only someone with the correct key can open it, and any tampering is immediately detectable.
Intuition anchor: cryptography transforms information into a form that is intelligible only to those authorized, forming the invisible shield of digital trust.