HMAC vs Digital Signatures: What's the Difference?

HMACs and digital signatures both let a recipient verify that a message is authentic and unaltered. They sound interchangeable, but they rest on different cryptography and prove different things. Choosing the wrong one can leave a real gap in your design.

The core difference: shared secret vs key pair

An HMAC uses a single shared secret that both the sender and verifier hold (symmetric). A digital signature uses a key pair: the sender signs with a private key, and anyone can verify with the matching public key (asymmetric). That one difference drives everything else.

What each one proves

An HMAC proves the message came from someone who holds the shared secret and wasn't altered. But because both parties share the key, the verifier could have produced the tag themselves — so an HMAC can't prove to a third party who created it. A digital signature proves the message was created by the holder of a specific private key, and because only they have that key, anyone with the public key can verify it — including a third party.

Non-repudiation

This leads to the key property: non-repudiation. A digital signature provides it — the signer can't later deny signing, because only their private key could have produced the signature. An HMAC does not provide non-repudiation, because either party with the shared secret could have created the tag. If you need to prove to an outsider who sent something — a signed contract, a software release — you need a signature, not an HMAC.

Speed and simplicity

HMAC's advantage is performance and simplicity. Symmetric operations are much faster than asymmetric ones, and there's no key-pair or certificate infrastructure to manage — just a shared secret. For high-volume internal use where both ends already share a key, HMAC is ideal.

When to use which

• Use HMAC when both parties can share a secret and you just need integrity and authenticity between them: API request signing, webhook signatures, and session tokens. It's fast and simple.
• Use a digital signature when verifiers shouldn't be able to forge messages, when you need non-repudiation, or when many independent parties must verify with a public key: TLS certificates, signed software, signed documents, and JWTs using RS256/ES256.

The JWT connection

JWTs illustrate both. An HS256 token is signed with an HMAC (shared secret) — great when the same party issues and verifies. An RS256 token uses a digital signature (private/public key) — better when many services verify tokens issued by one authority, since the verifiers can't mint their own. We cover this in what is a JWT.

Try it

Compute HMACs with our HMAC generator, and build HMAC- and signature-based tokens with the JWT generator and JWT decoder.