How Electronic Signatures Work
Understanding the technology, security, and authentication process behind electronic signatures. Learn how eSignatures ensure legal validity and document integrity.
Quick Answer
Electronic signatures work by capturing a user's intent to sign a document through authentication (verifying identity), creating a cryptographic signature using encryption keys, binding the signature to the document with a hash, and generating an audit trail. The entire process ensures the document cannot be altered after signing and provides legal proof of consent.
256-bit encryption + PKI
30 seconds average
Legally binding globally
What Is an Electronic Signature?
An electronic signature (eSignature) is a digital representation of a person's intent to agree to the contents of a document or contract. Unlike a wet ink signature on paper, an electronic signature uses cryptographic technology to bind a signer's identity to a document, creating a tamper-evident seal that proves authenticity and prevents document alteration.
Electronic signatures are legally binding in over 180 countries and are governed by laws like the U.S. ESIGN Act (2000) and UETA (Uniform Electronic Transactions Act). When implemented correctly, eSignatures are as legally enforceable as traditional handwritten signatures—and often more secure.
The Electronic Signature Process: Step by Step
When you sign a document electronically, several security and authentication steps happen behind the scenes to ensure legal validity and tamper protection.
Signer Authentication
Verifying the identity of the person signing
Before anyone can sign a document electronically, the eSignature platform must verify the signer's identity. This prevents unauthorized individuals from signing on behalf of someone else.
Authentication Method:
Email Verification
A unique signing link is sent to the signer's email address to verify their identity before they can sign the document.
Document Hashing
Creating a unique fingerprint of the document
Once the signer is authenticated, the eSignature platform creates a cryptographic hash of the document. A hash is like a digital fingerprint—a unique string of characters that represents the exact state of the document at the moment of signing.
// Example SHA-256 Hash (simplified)
Original Document:
"This is a contract between Company A and Company B..."
SHA-256 Hash:
5e884898da28047151d0e56f8dc6292773603d0d6aabbdd62a11ef721d1542d8
Why Hashing Matters:
Cryptographic Signature Creation
Encrypting the hash with the signer's private key
After the document is hashed, the eSignature platform uses Public Key Infrastructure (PKI) to create the actual electronic signature. This involves two cryptographic keys:
Private Key
A secret key known only to the signer, used to encrypt the document hash and create the signature.
Public Key
A publicly available key that anyone can use to verify the signature was created by the signer's private key.
How PKI Works:
- 1The signer's private key encrypts the document hash, creating the electronic signature.
- 2This signature is attached to the document along with the signer's public key.
- 3Anyone can use the public key to decrypt the signature and verify it matches the document hash.
- 4If the decrypted hash matches the current document hash, the signature is valid and the document is unaltered.
🔑 Why This Is Secure
Even if someone intercepts the document and signature, they cannot forge a new signature because they don't have access to the signer's private key. The private key is stored securely by the eSignature provider and never exposed.
Binding Signature to Document
Embedding the signature metadata into the file
Once the cryptographic signature is created, it's permanently embedded into the document file itself (usually as metadata in the PDF). This binding process ensures the signature cannot be copied to another document.
What Gets Embedded:
📄 PDF Signature Standards
Most eSignature platforms use the PAdES (PDF Advanced Electronic Signatures) standard, which is recognized internationally and ensures cross-platform verification.
Audit Trail Generation
Creating a tamper-proof record of the signing process
Every action taken during the signing process is recorded in a detailed audit trail. This provides legal evidence of who signed, when they signed, and what authentication methods were used.
Typical Audit Trail Contents:
- Document uploaded/created timestamp
- Email sent to signer with timestamp
- Document opened by signer (IP address, device info)
- Authentication method used and verification result
- Signature applied timestamp and location
- Completed document sent to all parties
⚖️ Legal Admissibility
Courts accept audit trails as evidence because they provide timestamped, tamper-proof documentation of the entire signing process, often stronger than witness testimony for handwritten signatures.
Security Features of Electronic Signatures
Modern eSignature platforms implement multiple layers of security to protect document integrity and prevent fraud:
256-Bit Encryption
All documents and signature data are encrypted using military-grade AES-256 encryption during transmission and storage.
Tamper-Evident Seals
Any modification to the document after signing breaks the cryptographic seal, making tampering immediately visible.
Email Authentication
Email verification ensures only authorized individuals with access to the specified email address can sign the document.
Timestamping
Trusted third-party timestamping services provide cryptographic proof of when a document was signed.
Frequently Asked Questions
Are electronic signatures as secure as handwritten signatures?
Yes, electronic signatures are often more secure than handwritten signatures. While handwritten signatures can be easily forged, electronic signatures use cryptographic technology, email authentication, and tamper-evident seals that make fraud nearly impossible. The audit trail provides stronger legal proof than a simple ink signature.
Can I verify an electronic signature myself?
Yes. Most signed PDFs allow you to verify the signature by opening the document in Adobe Acrobat Reader and clicking on the signature field. The software will check if the document has been altered since signing and display the signer's certificate details.
What's the difference between an electronic signature and a digital signature?
An electronic signature is any digital method of signing (typed names, scanned images, etc.), while a digital signature specifically refers to signatures using PKI encryption. Digital signatures are a more secure subset of electronic signatures. Learn more about the differences.
Do electronic signatures work on mobile devices?
Yes. Modern eSignature platforms like TurboSign are fully mobile-responsive, allowing signers to authenticate, review, and sign documents from smartphones and tablets using touchscreen signature capture.
How long does it take to sign a document electronically?
Most electronic signatures take 30-60 seconds to complete, including authentication. This is significantly faster than printing, signing, scanning, and emailing paper documents, which can take hours or days.
Are electronic signatures legally binding everywhere?
Electronic signatures are legally binding in most countries, including the U.S., Canada, EU member states, UK, Australia, and over 180 other jurisdictions. Read our guide on electronic signature legality.
Related Resources
Are Electronic Signatures Legal?
Learn about the legal framework behind electronic signatures including the ESIGN Act and UETA compliance.
How to Sign a PDF
Put your knowledge into practice with step-by-step instructions for signing PDFs electronically.
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