Hash, Encryption and Digital Signature: Three Different Tools

Hash functions, encryption, and digital signatures are often mentioned together in discussions of blockchain and data security. They are related — all three are cryptographic tools — but they do different things and should not be confused.

A hash function takes an input of any size and produces a fixed-length output, called a hash or digest. SHA-256, used in Bitcoin, always produces a 256-bit output regardless of whether the input is a single character or a gigabyte of data.

Hash functions are one-way: you can compute the hash from the input, but you cannot reconstruct the input from the hash. They are also deterministic: the same input always produces the same hash. And they are collision-resistant: it is computationally infeasible to find two different inputs that produce the same hash.

Use case: verifying data integrity. If you hash a file before and after transmission, and the hashes match, the file has not been altered.

Encryption transforms data into an unreadable form that can be reversed — decrypted — by someone with the correct key. Unlike hashing, encryption is reversible.

Symmetric encryption uses the same key to encrypt and decrypt. Asymmetric encryption uses a key pair: a public key to encrypt, a private key to decrypt (or vice versa for signatures).

Use case: protecting data in transit or at rest. HTTPS uses asymmetric encryption to establish a session key, then symmetric encryption for the data.

A digital signature uses asymmetric cryptography to prove that a message was created by a specific private key holder and has not been altered since signing.

The process: the signer hashes the message, then encrypts the hash with their private key. The recipient decrypts the hash with the signer's public key and compares it to a fresh hash of the message. If they match, the signature is valid.

Use case: authorising transactions on a blockchain. When you send crypto, you sign the transaction with your private key. The network verifies the signature with your public key.

This article is for information only.