Digital Signatures: What They Are & How They Work

Learn why Top Industry Analysts consistently name Okta and Auth0 as the Identity Leader

A digital signature uses a mathematical algorithm to guarantee secure message transmission and authenticity.

Digital signatures use asymmetric cryptography and rely on the PKI (public key infrastructure). A digital signature provides a high level of security and is backed by a standard, publicly trusted, and universal format.

Digital signatures are legally binding, and the PKI can ensure that the message is authentic and retains its integrity. Digital signatures often require the use of a certificate authority (CA), which is a trusted signer for the public key.

Digital signatures can prove the authenticity of a sender. With the use of a matching private key, they make sure that only the intended recipient can read it.

What is a digital signature?

An authentication mechanism, a digital signature is a type of code that is attached to a message by a sender that verifies that they are who they say they are. It associates a particular signer with a specific document.

In this way, a digital signature is unique to the creator and signer of the message. Each signer will have a specific private key that will need to be matched to a corresponding public key for verification and authentication purposes.

A digital signature is a form of cryptography that uses the public key infrastructure, or PKI, to securely transmit messages and authenticate senders. Digital signatures require both a public and a private key to be decrypted. The public key will be signed by a trusted CA and will need to match the private key.

A digital signature can offer a high level of security, as it helps to verify the integrity of messages and authenticity of the sender.

Differences between a signing certificate and certificate authority

A code signing certificate is a digital certificate that is signed by the developer of software or a particular application. This can help to authenticate that the product is real and has not been tampered with or altered. They are not, however, signed by a public certificate authority.

A code signing certificate can be a helpful tool when downloading software or an application from a third-party website or organization to ensure that it is legitimate and what you are actually trying to access.

A certificate authority, on the other hand, is a highly vetted and publicly trusted entity that signs public keys for the PKI. These keys are widely available and distributed. The CA often signs public keys for the TLS/SSL (Transport Layer Security/ Secure Sockets Layer) protocol, which can authenticate websites to web browsers.

Only the trusted CA can sign digital certificates to validate and authenticate the identity of the user with the matching private key.

Benefits of a digital signature

A digital signature can work the same way as a traditional pen-and-paper signature, offering verification of the identity of the signer. A digital signature offers the following benefits:

  • Heightened security: Digital signatures contain “fingerprint”-type data that is unique and permanently embedded within the document. The coded message contained within the digital signature can identify and verify the signer and link them with the specific recorded document. The PKI encryption verification technology is considered one of the most secure and verifiable standards for identification authentication.  
  • Independent verification and integrity: Highly regarded companies providing digital signatures can hold up through independent verification methods. Message integrity is guaranteed as the digital signature cannot be altered by a third party.  
  • Legal compliance and wide acceptance: Digital signatures are being globally accepted as legally binding. Laws such as the Electronic Signatures in Global and National Commerce Act (E-Sign Act) regulate companies providing digital signatures as well as prove their legal status.  
  • Speed and efficiency: The electronic signing of a document can be done easily and quickly, saving the time and money required with in-person document signing and manual data entry. This can make the transaction cost lower and the experience more user-friendly.  
  • High standard: The PKI is highly regarded, and CAs are strictly regulating, which elevates public trust and can ensure message integrity, verification of identification, and authenticity  

How digital signatures work

Digital signatures use complex mathematical algorithms, such as the following three:

  1. Key generation algorithm: This selects a private key and matches it with a corresponding public key that is generated and provided by a trusted CA.  
  2. Signing algorithm: This produces the signature using a cryptographic hash, such as the digital signature algorithm (DSA) developed by the National Institute of Standards and Technology (NIST).  
  3. Signature verifying algorithm: This will check the encrypted signature and the private key against the matching public key for authentication.

The first mathematical algorithms are used to create two long numbers, or keys — both of which are required to encrypt and decrypt the message. The private key is kept by the signer and used to create the unique digital signature. The second algorithm creates the cryptographic hash, working like a cipher, to encrypt the data. This becomes the digital signature, which will also contain a timestamp of when it was signed.

The third algorithm checks the public key, which is sent along with the signed document. It should be able to decrypt the signature from the cipher that created the keys. When this matches, the digital signature is verified, and the message is decrypted. If the digital signature does not match or the document was altered after signing, the digital signature is invalidated.

PKI is a specific protocol involving reliable CAs, and digital signature providers are required to meet PKI requirements. The PKI protocol can ensure security and trusted authentication and verification methods.

Who uses digital signatures?

Digital signatures are used globally through a variety of industries and identity verification purposes. They are used by individuals to sign individual documents in a secure manner as well as by email service providers to ensure that messages remain between the sender and intended recipient.

Digital signatures are also used by software developers to prove the authenticity of their product. Another use for digital signatures is for financial transactions, which are required to be secure, and identity verification is crucial.

Digital signatures using PKI involve a trusted third party that can keep data secure and ensure the integrity of messages and documents. As more and more transactions and interactions are moving to an online format, the importance of digital signatures becomes even greater.

Key takeaways

Digital signatures are similar to traditional signatures; however, they involve complex mathematical algorithms and cryptographic methods.

Digital signatures involve asymmetric cryptography, and they generate both a public and a private key to encrypt and decrypt messages. The public key is signed by a trusted public certificate authority and uses the public key infrastructure (PKI) protocol.

In addition to the corresponding keys, another algorithm creates the actual digital signature, which uses a cryptographic hash function to sign. The signature is then attached to a document and time stamped. If the document is altered after the signing, it will be obvious that the document has been tampered with and the signature is no longer valid.

Digital signatures using the PKI protocol adhere to a high industry standard. They can provide a heightened sense of security and ensure the integrity of the document or data as well as ensure the authenticity of the sender. Digital signatures are legally binding and accepted globally as valid methods of identity verification and document security and integrity.



Electronic Signatures in Global and National Commerce Act. (January 2014). FDIC Consumer Compliance Examination Manual.

Digital Signature Algorithm (DSA). National Institute of Standards and Technology (NIST).

Understanding Digital Signatures. (August 2020). Cybersecurity & Infrastructure Security Agency (CISA).