Digital Signature

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What is a Digital Signature?

The definition of a digital signature is a cryptographic technique used to validate the authenticity and integrity of digital messages or documents. It is the digital equivalent of a handwritten signature or a stamped seal, but it offers far more inherent security, as it uses encryption techniques to provide authentication of original and unmodified documentation.


Digital signatures are used in e-commerce, software distribution, financial transactions, and other situations that rely on techniques to detect forgery or tampering.

What is a Digital Signature?

Key Takeaways

  • A digital signature ensures the sender of a message is who they claim to be.
  • A digital signature can be used to verify that a piece of content has not been altered since it was signed.
  • The signer cannot deny having signed a document using a digital signature.
  • Digital signatures are legally binding in many countries.
  • Digitalizing signatures streamlines processes by reducing paper use and speeding up transactions.

How a Digital Signature Works

How a Digital Signature Works

A digital signature works using a process called public key infrastructure (PKI).

It is applied and verified as follows:

  1. The document is passed through a hashing algorithm, generating a unique hash value.

  2. This hash value is encrypted using the sender’s private key, creating the digital signature.

  3. The sender, using the private key, appends the encrypted signature to the message or document to sign it digitally.
  4. The document or message sender (signer) or public/private key supplier shares the public key with the recipient(s).
  5. The recipient decrypts the hash using the sender’s public key. If the decrypted hash matches a new hash created from the document, the signature is verified, which lets the recipient know that the document is from the original sender. 

Digital Signature vs. Electronic Signature

While it might be tempting to use the terms interchangeably, there is a distinction between a digital signature and an electronic signature.

  • Digital signature: Uses cryptographic methods to secure the document and verify the signer’s identity.
  • Electronic signature: Any electronic indication of intent to sign a document (e.g. a scanned image of a handwritten signature) without inherent security features.

Digital Signature vs. Electronic Signature

Types and Classes of Digital Signatures

There are different types of digital signatures based on their security features, legal standing, and the level of assurance they provide. Understanding these distinctions helps users choose the right type of digital signature for their specific needs.

Simple Digital Signatures

Simple digital signatures, also known as basic electronic signatures, provide a basic level of security and are often used in low-risk scenarios. They do not require any form of identity verification. They are typically easy to create and implement and are mainly used in informal agreements, non-sensitive communications, and internal company approvals to confirm the intent to sign a document.

Advanced Digital Signatures

Advanced digital signatures require the signer to be uniquely linked to and identified by the signature, ensuring that any change to the signed data is detectable. These signatures use cryptographic methods for higher security.

The signer’s identity is verified through digital certificates issued by trusted certificate authorities (CAs). Any alteration to the signed document invalidates the signature. As this provides a higher level of assurance compared to simple digital signatures, advanced signatures tend to be used in legal contracts and agreements, financial transactions, and sensitive corporate communications.

Qualified Digital Signatures

Qualified digital signatures are subject to strict regulatory standards and are equivalent to handwritten signatures in the eyes of the law in many jurisdictions. These signatures are created using a qualified signature creation device (QSCD) and are backed by a qualified certificate issued by a trusted certification authority, providing the highest level of security and legal acceptance. A qualified digital signature is strongly linked to the signer’s identity, providing irrefutable evidence of the signer’s intent. This makes it suitable for high-value transactions, legal and regulatory documents, and government forms and applications.

Digital signatures are also classified into three different main classes based on their use and the level of trust they provide.

Class 1 signatures
Intended for use in environments where there is minimal risk. They provide basic assurance and are typically used for internal company documents and non-critical email communications.

Class 2 signatures
Used in environments with a moderate level of risk. They provide a higher level of assurance compared to Class 1 and are often used for business transactions where identity verification is important, e-filing of tax returns, and online banking transactions.

Class 3 signatures
Offer the highest level of assurance and are used in environments where there is a high risk of data compromise. These signatures require the signer to be present before a certifying authority to verify their identity. Uses include high-value business transactions, court documents, and government applications requiring the highest level of trust.

Why Should You Use PKI or PGP With Digital Signatures?

Public Key Infrastructure (PKI) and Pretty Good Privacy (PGP) are systems that manage keys and certificates, ensuring the security and integrity of digital signatures. They provide robust frameworks for key management, handling the creation, distribution, and revocation of keys. They ensure that only authorized parties can access the signed documents.

Digital Signature Uses

  • Ensuring the authenticity and integrity of contracts and agreements.
  • Verifying the sender and content of emails.
  • Confirming the origin and integrity of distributed software.
  • Securing online banking and transactions.
  • Signing court documents.
  • Submitting application forms and other documents to government agencies.

Digital Signature Attacks

While digital signatures are encrypted and designed to be more secure than physical signatures, they can be vulnerable to cyberattacks, such as:

Man-in-the-Middle (MitM) attack

Fraudulent attempts to obtain sensitive information by disguising it as a trustworthy entity.

You should consider using a password manager to protect a digital signature’s private key from unauthorized access.

Digital Signature Security

There are several steps to ensuring the security of digital signatures:

  • Use strong encryption – employ robust algorithms and key lengths.
  • Regularly update software to protect against vulnerabilities.
  • Employ multifactor authentication (MFA) to add an extra layer of security.
  • Regularly review security policies to stay on top of new threats and technologies.

Digital Signature Pros and Cons


  • Enhanced security and trust
  • Legally binding
  • Reduces paperwork and speeds up transactions
  • Verifies document integrity


  • Requires technical infrastructure
  • Potentially vulnerable to sophisticated attacks
  • Legal acceptance varies by country

The Bottom Line

The meaning of a digital signature is a way of signing documents electronically, providing a secure, efficient, and legally recognized way to authenticate them. By understanding the digital signature process and employing best practices, individuals and organizations can enhance their security posture and streamline their operations.


What is a Digital Signature in simple terms?

How do I do a digital signature?

What is a simple example of a digital signature?

What are the three types of digital signatures?


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Nicole Willing
Technology Journalist
Nicole Willing
Technology Journalist

Nicole is a professional journalist with 20 years of experience in writing and editing. Her expertise spans both the tech and financial industries. She has developed expertise in covering commodity, equity, and cryptocurrency markets, as well as the latest trends across the technology sector, from semiconductors to electric vehicles. She holds a degree in Journalism from City University, London. Having embraced the digital nomad lifestyle, she can usually be found on the beach brushing sand out of her keyboard in between snorkeling trips.