Cipher

A cipher is a cryptographic algorithm, a set of well-defined rules used to encrypt readable data (plaintext) into unreadable data (ciphertext), and to decrypt ciphertext back into plaintext. Ciphers are foundational to modern cryptography because they let people and systems exchange information privately, even over public networks.

Encryption with a cipher typically involves an input message and a key. The key is a secret value (or, in some designs, one of a public and private pair) that controls the transformation. Without the correct key, ciphertext should be computationally infeasible to reverse into the original plaintext. This is what makes encrypted data safe to store, transmit, and verify in hostile environments.

There are two broad ways ciphers are used. In symmetric encryption, the same secret key encrypts and decrypts, which is efficient for large amounts of data. In asymmetric, or public-key cryptography, one key encrypts and a different key decrypts, enabling secure communication without first sharing a secret in person.

Blockchains rely on cryptography in multiple layers, and ciphers are a core tool for protecting wallets, nodes, and users. For example, many wallets encrypt sensitive material such as private keys or seed phrases at rest, meaning on your device, using a cipher and a key derived from your password. Network connections between nodes can also use encryption to reduce the risk of eavesdropping and tampering.

It is important to distinguish ciphers from hash functions and digital signatures. Hashes help ensure data integrity, and signatures prove authorization, while ciphers focus on confidentiality by keeping information secret.