Digital Signature vs. Electronic Signature

What’s the Difference?

This is the distinction most people miss — and it matters more than you’d think.

What Is an Electronic Signature?

An electronic signature (or e-signature) is essentially a digital representation of your signature — an image, a typed name, or a drawn mark applied to a document. E-signatures are fast and convenient, and they work well for low-risk, everyday documents.

The limitation: most e-signatures don’t use cryptographic protection. That means there’s no built-in mechanism to detect whether the document was altered after it was signed.

What Is a Digital Signature?

A digital signature goes much further. It uses PKI — Public Key Infrastructure — to create a unique cryptographic seal that is mathematically tied to both the signer’s identity and the exact content of the document at the moment of signing.

If anything in the document changes after signing — even a single character — the seal breaks visibly. Tampered documents are immediately detectable.

In short:

  • Electronic signature = a mark on a document
  • Digital signature = a cryptographic lock on a document

What is Public Key Infrastructure – PKI

cryptographic system that uses two keys, a public key known to everyone and a private key, the private key has full control to the key owner, and has to keep in secured environment. A unique element to the public key system is that the public and private keys are related in such a way that only the public key can be used to encrypt messages and only the corresponding private key can be used to decrypt them. Moreover, it is virtually impossible to deduce the private key if you know the public key.

When David wants to send a secure message to Donna, he uses Donna’s public key to encrypt the message. Donna then uses her private key to decrypt it.

Public key cryptography was invented in 1976 by Whitfield Diffie and Martin Hellman. It is also called asymmetric encryption because it uses two keys instead of one key (symmetric encryption).

Generating a Private and Public Key

Before David can digitally sign any documents, he must first obtain a Private Key and a corresponding Public Key. This is a one-time setup that is typically done by the Secured Signing Service when David first registers.

  • The Private Key is kept secret and is used only by David to sign documents. It is never shared.

  • The Public Key is made available to everyone (including Donna). It is used to validate the signer’s (David’s) digital signature.

Generating a Private and Public Key

Digitally Signing Document

This section details the steps David takes to sign a document and what happens when he sends it to Donna.

Create a Digital Signature

First, a unique cryptographic code called a hash is generated for the document using a mathematical algorithm. This hash is a short string of characters that represents the entire document.

Even a tiny change to the document will result in a completely different hash.

Add the Digital Signature to the Document

To create the final digital signature, the following elements are combined:

  • The document’s hash (from step 1).

  • David’s Digital Certificate (which contains his Public Key).

This is done by using David’s Private Key to encrypt the document’s hash.

The resulting digital signature is unique to both the document and David. Finally, this digital signature is embedded into the document.

David then sends the signed document to Donna.

Donna’s Validation Process

    1. Donna uses David’s Public Key (included in the Digital Certificate) to decrypt the digital signature. This action reveals the original document hash that David created when he signed the document.
    2. Donna compares the original hash (extracted from the signature) with the new hash (she just calculated).

    3. Determine Validity:

      • If the hashes match: The signature is valid, and the document has not been altered since David signed it.

      • If the hashes do not match: The document has been changed after signing, or the signature is invalid.

signing a secured signing document
verified signed document

What is a Certificate Authority (CA)

A Certificate Authority (CA) is a trusted third party that issues digital certificates.

  • Digital Certificates act like a digital ID card, confirming the identity of a signatory (user).

  • The CA issues a certificate after verifying the user’s information.

  • In a digital signature system (PKI), the CA uses its own authority to authenticate the user’s certificate, assuring others that the signatory is genuinely who they claim to be.

How Do Digital Signatures Work?

Digital signatures use a two-key system:

  1. Private key — held securely by the signer, used to create the signature
  2. Public key — available to anyone who needs to verify the signature

When you digitally sign a document, the software generates a unique hash (a mathematical fingerprint) of that document’s contents and encrypts it with your private key. Anyone receiving the document can use your public key to decrypt and verify the hash. If the document content matches the hash, the signature is valid. If anything has changed, it won’t match — and the document is flagged as compromised.

This process is what makes digital signatures tamper-proof, not just tamper-evident.


Why Does This Difference Matter?

For low-stakes documents — internal approvals, informal agreements — a basic e-signature is often enough.

But for anything that carries legal, financial, regulatory, or compliance weight, the type of signature you use matters significantly:

  • Legal enforceability: Digital signatures provide a stronger, more auditable proof of signing intent and document integrity.
  • Regulatory compliance: Industries like healthcare (HIPAA), life sciences (21 CFR Part 11), and financial services often require or strongly favour PKI-based digital signatures.
  • Fraud prevention: Because the signature is cryptographically tied to the document, any post-signing alteration is immediately detectable.
  • Trust: Every party — signer, recipient, regulator — can independently verify that a digitally signed document hasn’t been changed.

What Makes a Digital Signature Tamper-Proof?

Tamper-proof means the document cannot be altered without detection. With PKI digital signatures, the moment any change is made to a signed document — a word edited, a clause removed, a number adjusted — the cryptographic hash no longer matches. The signature becomes invalid, and the broken seal is visible.

This is fundamentally different from a document signed with a basic e-signature, where the signature image can often remain in place even if the underlying document is edited.

 

Sign smarter, faster, and safer with Secured Signing — tamper-proof digital signatures that protect every document from first click to final seal.