A digital signature is a cryptographic proof created by hashing data and signing the hash with a private key. Anyone with the matching public key can verify the signer's identity and that the data is unchanged.
Why it matters
Signatures provide authenticity, integrity and non-repudiation. They underpin TLS certificates, software updates, signed emails, DKIM and JWTs. A changed byte anywhere in the data makes verification fail, so tampering is detectable.
Example
A software vendor signs an installer. Your operating system verifies the signature with the vendor's public key before running it, and shows a warning if the file was modified or the signer is unknown.
Common mistakes
- Confusing it with an image of a handwritten signature.
- Signing without protecting the private key, so others can forge signatures.
- Verifying the signature but not checking that the public key truly belongs to the claimed signer.
Related
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