How Does Digital Signature Work?

• A digital signature is a secure method to sign digital documents using cryptography, ensuring the document is authentic, unchanged, and legally binding.
  
• A digital signature is created with a private key and verified with a public key, as part of public key infrastructure (PKI), which guarantees the signer's identity and protects against tampering.
  
• pdfFiller excels at editing and managing PDFs and supports electronic signatures, which are suitable for many use cases.
  
• A digital signature generates a unique encrypted “fingerprint” of the document, ensuring that even the smallest change (like altering a single character) invalidates the signature and alerts recipients to tampering.
  
• Trusted Certificate Authorities (CAs) issue and manage digital certificates that validate the signer’s identity, making digital signatures legally recognized and compliant with regulations like eIDAS and ESIGN.
  

What is a digital signature?

A digital signature is a cryptographic method used to verify the authenticity and integrity of digital documents. It ensures a document has not been altered and was signed by the claimed person. Unlike handwritten signatures, digital signatures use advanced encryption techniques, such as public-key cryptography, to provide heightened security. They are legally recognized in many jurisdictions under regulations like the EU’s eIDAS and the US’s ESIGN Act.

Methods for creating digital signatures

There are several ways to create digital signatures, each suited to different needs and security levels. The table below compares common methods:

How does a digital signature work step by step?

Digital signatures use public key infrastructure (PKI) to ensure a document’s authenticity and integrity. Here’s the process:

1. Key Generation: The signer generates a key pair—a private key (kept secret) and a public key (shared openly).
   
2. Hashing the Document: A hash function processes the document, creating a unique fixed-length string (hash) that represents its content.
   
3. Signing the Hash: The signer encrypts the hash with their private key, creating the digital signature.
   
4. Attaching the Signature: The digital signature is attached to the document, along with the signer’s public key or a digital certificate.
   
5. Verification: The recipient uses the signer’s public key to decrypt the signature, retrieving the original hash.
   
6. Comparing Hashes: The recipient hashes the received document and compares it with the decrypted hash. If they match, the signature is valid, confirming the document’s integrity and authenticity.
   

This process ensures the document hasn’t been tampered with and was signed by the rightful owner of the private key.

How do I create a digital signature using pdfFiller?

Creating a digital signature involves these steps:

1. Obtain a Digital Signature Certificate: Contact a trusted Certificate Authority (CA) to verify your identity and receive a digital certificate linking your public key to your identity.
   
2. Choose a Signing Tool: Use software or services that support digital signatures. While pdfFiller excels at PDF editing and supports electronic signatures (e.g., drawing or typing your name), cryptographic digital signatures require third-party tools.
   
3. Sign the Document: Follow the tool’s instructions to sign the document using your private key, which is typically stored securely in software or a hardware token.
   

pdfFiller’s robust PDF editing capabilities make it ideal for preparing documents before signing. For cryptographic digital signatures, integrate with third-party services that specialize in digital signature technology. Follow these steps:

1. Contact a trusted Certificate Authority (CA) like GlobalSign or DigiCert.
   
2. They verify your identity and issue a certificate with your public key.
   

1. Use free tools like OpenPGP or GnuPG for signing.
   
2. These work across platforms and don’t need pdfFiller’s built-in support.
   

1. Open the document in the software.
   
2. Select "Sign," choose your certificate, and apply the signature.
   
3. Save or export the signed file.
   

  With pdfFiller, prepare your document first, then export it for signing in a third-party tool.

How to get a digital signature to work?

To ensure a digital signature functions correctly:

• Use Trusted Sources: Obtain your digital signature certificate from a reputable CA to ensure trust and recognition.
  
• Secure Your Private Key: Keep your private key confidential and store it in a secure environment, such as a hardware security module or encrypted software.
  
• Choose Compliant Tools: Use software or services that meet legal standards and security requirements, such as eIDAS in the EU or ESIGN Act in the US.
  
• Verify Regularly: Ensure recipients can verify the signature using your public key or certificate.
  

Understanding key components: Private key, public key, and certificate authority

To fully grasp how digital signatures work, it’s essential to understand three key components: the private key, the public key, and the certificate authority. These elements form the backbone of the cryptographic process that makes digital signatures secure and trustworthy.

Private key

A private key is a secret code known only to the signer. It is used to create the digital signature by encrypting the document’s hash. Think of it like a unique, unforgeable stamp that only you possess. The security of a digital signature relies on keeping the private key confidential—if someone else gains access to it, they could create fraudulent signatures in your name. For this reason, private keys are often stored in secure environments, such as encrypted software or hardware tokens.

Public key

A public key is the counterpart to the private key and is shared openly. It allows others to verify the digital signature by decrypting the hash and confirming the document’s authenticity. While the private key is like a secret stamp, the public key is like a verification tool that anyone can use to check if the stamp is genuine. The public key cannot be used to create signatures, only to verify them, ensuring that only the private key holder can sign documents.

Certificate Authority (CA)

A certificate authority (CA) is a trusted organization that issues digital certificates, which link a public key to a verified identity. When you obtain a digital certificate from a CA, they confirm your identity—similar to how a government issues a driver’s license. This certificate is attached to your signed documents, allowing recipients to trust that the public key belongs to you. CAs play a critical role in establishing trust in digital transactions, especially in industries like finance, healthcare, and law, where identity verification is paramount.

By understanding these components, you can appreciate how digital signatures provide a secure, verifiable way to sign digital documents. The private key ensures only you can sign, the public key allows others to verify, and the certificate authority confirms your identity, creating a chain of trust.

How is a digital signature verified?

Verifying a digital signature ensures the document’s authenticity and integrity:

1. Obtain the Signer’s Public Key: This is usually included in the digital certificate attached to the document.
   
2. Decrypt the Signature: Use the public key to decrypt the digital signature, revealing the original hash.
   
3. Hash the Document: Create a hash of the received document using the same hash function as the signer.
   
4. Compare Hashes: If the hashes match, the signature is valid, confirming the document hasn’t been altered and was signed by the holder of the corresponding private key.
   

What are the benefits of using digital signatures?

Digital signatures offer significant advantages over traditional handwritten signatures:

• Security: Cryptographic techniques prevent forgery and tampering.
  
• Authenticity: They confirm the signer’s identity through a trusted certificate authority.
  
• Integrity: They ensure the document remains unchanged after signing.
  
• Non-repudiation: The signer cannot deny signing the document.
  
• Convenience: They enable remote signing without physical presence.
  
• Cost Savings: They reduce reliance on paper, printing, and storage.
  

Digital signatures are widely used in financial transactions, patient records, legal contracts, and software distribution, where trust and security are paramount.

Digital signatures vs. Electronic signatures

Understanding the difference between digital signatures and electronic signatures is crucial:

• Electronic signatures: A broad category that includes any electronic method to indicate intent to sign, such as typing your name, using a stylus, or clicking “accept” on a contract.
  
• Digital signatures: A specific type of electronic signature that uses cryptographic techniques, such as public-key infrastructure, to ensure authenticity and integrity. They offer heightened security and are often required for legally binding documents.
  

pdfFiller supports electronic signatures, making it easy to add typed or drawn signatures to PDFs. For cryptographic digital signatures, consider third-party tools that provide digital certificates.

Legal standards for digital signatures

Digital signatures are legally binding in many jurisdictions, provided they meet specific standards:

• eIDAS (EU): The Electronic Identification, Authentication and Trust Services regulation defines standards for electronic signatures, including Advanced Electronic Signatures (AES) and Qualified Electronic Signatures (QES), with QES offering the highest assurance.
  
• ESIGN Act (US): The Electronic Signatures in Global and National Commerce Act recognizes electronic signatures as legally binding, provided they meet certain criteria.
  

Always ensure compliance with local regulations to avoid legal issues. pdfFiller adheres to industry standards for document management, ensuring secure handling of your PDFs.

Final thoughts

Digital signatures are a cornerstone of secure digital communication, ensuring authenticity, integrity, and non-repudiation for digital documents. They are essential for businesses and individuals handling sensitive transactions, from contracts to financial records. pdfFiller, a leading PDF solution trusted by millions, excels at editing and managing PDFs, including adding electronic signatures. For cryptographic digital signatures, you can integrate pdfFiller with third-party services that specialize in digital signature technology.

Start your free trial with pdfFiller today and streamline your PDF workflow with ease and efficiency. Whether you’re preparing documents for signing or managing business workflows, pdfFiller has you covered.

Glossary

• Digital signature: A cryptographic method to verify the authenticity and integrity of digital documents.
  
• Private key: A secret key used by the signer to create a digital signature.
  
• Public key: A publicly available key used to verify a digital signature.
  
• Hash function: A mathematical function that converts a document into a fixed-length string (hash) to ensure integrity.
  
• Certificate Authority (CA): A trusted entity that issues digital certificates to verify identities.
  

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