What is Digital Signature?

A cryptographic mechanism that proves the authenticity and integrity of a message or document, confirming it was created by the claimed sender and hasn't been altered.

Digital signatures provide non-repudiation — proof that a specific party signed a specific message.

How It Works

Signer hashes the message
Encrypts the hash with their private key (this is the signature)
Sends the message and signature
Recipient hashes the message independently
Decrypts the signature with the signer's public key
If the hashes match, the signature is valid

Common Algorithms

Ed25519: Fast, secure, deterministic. Recommended for new systems.
RSA-PSS: Based on RSA. Widely supported.
ECDSA: Elliptic curve. Used in Bitcoin and TLS.

Applications

Software code signing (verifying updates are genuine)
Email signing (PGP, S/MIME)
Cryptocurrency transactions
Document signing (contracts, certificates)
TLS certificates

Related Terms

Hash Function

A mathematical function that converts any input data into a fixed-size string of characters (hash). Cryptographic hash functions are one-way, meaning you cannot reverse the process to recover the original data.

PGP

Pretty Good Privacy (PGP) is an encryption program that provides cryptographic privacy and authentication for data communication. It's used for signing, encrypting, and decrypting texts, emails, files, and directories, and is the gold standard for email encryption.

Public Key Cryptography

A cryptographic system that uses pairs of keys: public keys (which may be disseminated widely) and private keys (which are known only to the owner). This enables secure communication between parties who have never met and forms the basis for digital signatures, key exchange, and encrypted communication.

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