Electronic signature vs. digital signature: what's the difference?

Jakub Król

Hands typing on a laptop at a bright white desk

People use "electronic signature" and "digital signature" as if they mean the same thing. They don't. An electronic signature is a legal idea: any electronic way of showing you agree to a document. A digital signature is a specific technology: a way of using encryption to prove who signed a file and that it has not changed since.

Every digital signature can serve as an electronic signature, but most electronic signatures are not digital signatures. For nearly all business agreements in the United States, an ordinary electronic signature is all the law asks for.

In this article

What an electronic signature is

The federal ESIGN Act defines an electronic signature as an electronic sound, symbol, or process attached to or logically associated with a record and adopted by a person with the intent to sign it. That covers a lot:

  • A signature drawn with a finger or mouse
  • A typed name
  • A clicked "I agree" box, when it is clearly tied to a specific document
  • A recorded "yes" on a phone call, in some settings

The definition is deliberately technology-neutral. What makes an electronic signature count is the signer's intent, their consent to do business electronically, and a record that ties the signature to the document. We cover those requirements in detail in are electronic signatures legally binding?

What a digital signature is

A digital signature is a cryptographic technique built on public-key encryption. The signer has two linked keys: a private key that only they control, and a public key anyone can see.

  1. The software calculates a short fingerprint of the file, called a hash.
  2. That hash is encrypted with the signer's private key. The result is the digital signature, which is attached to the file.
  3. Anyone can decrypt it with the signer's public key and compare it with a fresh hash of the file. If they match, the file is unchanged and was signed with that private key.

On its own, that proves which key signed, not which person. To link the key to a real identity, a certificate authority issues a digital certificate after checking who the key holder is. This is what you see when a PDF viewer shows a signature panel saying the document was signed by a named person and has not been modified since.

The difference, side by side

  • What it is. An electronic signature is a legal category. A digital signature is an encryption method.
  • What it proves. An electronic signature shows intent to sign, backed by whatever evidence was collected. A digital signature proves mathematically that the file is unchanged and was signed with a particular key.
  • Identity. An electronic signature usually relies on evidence such as the email address the signing link was sent to. A digital signature can carry an identity checked by a certificate authority.
  • What signers need. An electronic signature needs nothing but a browser. A certificate-based digital signature often needs the signer to obtain a certificate first.

The two are not rivals. Many e-signature services capture a simple electronic signature from each person and then use cryptography to protect the finished document.

How Inkly protects a signed document

Inkly captures a simple electronic signature from each signer and records the evidence around it: a private signing link sent to each signer's own email address, timestamps for every step, and the IP address, approximate location, and device used. When the last person signs, Inkly calculates a SHA-256 hash of the completed PDF and prints it on the Certificate of Completion. Recompute the hash of any copy and compare: if a single byte has changed, the values will not match. You can see a full example in our guide to what an electronic signature audit trail records.

That fingerprint makes tampering detectable, but it is not a certificate-based digital signature. Inkly does not issue certificates from a certificate authority, so if a regulator or counterparty specifically requires one, you need a provider that does.

When the law asks for a digital signature

In the United States, almost never for everyday agreements. ESIGN and UETA do not require encryption or certificates, so sales contracts, NDAs, offer letters, leases, and consent forms are all fine with a simple electronic signature. A few regulated filings and government systems set their own technical rules, and they say so in their instructions.

In the European Union, the eIDAS regulation defines three levels of electronic signature:

  • Simple electronic signature. The everyday level, suitable for most contracts.
  • Advanced electronic signature. Uniquely linked to and capable of identifying the signer, under their sole control. Usually built on a digital signature.
  • Qualified electronic signature. An advanced signature backed by a qualified certificate from an approved trust provider. It is the only level automatically treated as equal to a handwritten signature in every member state.

Some member states require a qualified signature for particular documents. Our compliance page explains which level Inkly provides.

Which one you need

For most small businesses, the answer is a simple electronic signature with a strong audit trail. It is legally binding, signers need no account or certificate, and the evidence holds up when someone disputes a signature.

You need a certificate-based digital signature when a law, regulator, or government portal names one, when you are signing an EU document that requires an advanced or qualified signature, or when the other party insists on one. Notarized documents are a separate question, covered in whether electronic signatures need a witness or a notary.