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Difference Between Digital Signature and Digital Certificate

Lumena Mukherjee
SectigoStore is the Platinum Partner of Sectigo CA (previously known as Comodo CA). We offer website security products.
・4 min read

Starting with man-in-the-middle attacks to fake illegitimate websites, attackers have often taken it upon themselves to sniff out our credentials, conversations, or other sensitive details. Fortunately, we have technologies that we can leverage to secure our communications. With HTTPS, it is now possible to set up a secure connection between two endpoints. Similarly, it is possible to digitally sign our emails, software, etc. Digital certificates and digital signatures provide a way to encrypt our data and assure its legitimacy in terms of who is sending the message or if the server you’re connecting to is who it says it is. Let’s understand what they are and the role they play in securing our communication.

What is a Digital Signature?

The National Institute of Standards and Technology (NIST) issued the Digital Signature Standard (DSS) in 1991. It uses the Digital Signature Algorithm (DSA), a Federal Information Processing Standard, based on public-key cryptography. A digital signature is a cryptographic technique that provides message integrity, authentication, and non-repudiation to a message, software, or digital document. It validates the sender’s identity and assures that the message is free from any undesirable alterations. A digital signature is associated with two keys – public and private. The public key is used to validate the sender's authenticity, and the private key is used to create the signature itself. Presume two friends, Alice and Todd, want to communicate securely and ensure that the message truly is coming from the other, without being modified. Let’s see how this would work if Alice were to send a message to Todd.

  • Alice generates a one-way hash of the message (if she were signing a software, she would hash the executable file) and encrypts it using her private key.
  • Next, the message along with the digital signature is transmitted.
  • Todd decrypts the hash using Alice’s public key. This step verifies that Alice indeed sent the message since only she could encrypt the message with the corresponding private key.
  • Todd then creates a new hash of the message and compares it with the one generated by Alice. The two values must match in order to maintain integrity.
  • If they do, it indicates the message hasn’t been tampered with since Alice last signed it.

What is a Digital Certificate?

Digital certificates, also known as SSL/TLS certificates, are a type of X.509 certificates. They are used to establish an encrypted communication channel between the client and the server. Every time you visit a site with a padlock running over HTTPS, you’re communicating via a secured link that uses SSL certificates. According to Research and Markets, the global market value of digital certificates is projected to grow 10% annually to $123.8 million in 2023. These certificates are typically issued by trusted third party certificate authorities (CA). The time and effort required depends upon the validation level of the certificate (domain validation, organization validation, or extended validation). The CA assesses and verifies the evidence submitted before signing and sending a certificate to the applicant.

Digital Signature vs. Digital Certificate

Though both digital certificates and digital signatures are both used to communicate securely, one secures the actual data, and the other establishes trustworthiness. Let’s take a look at the table below to better understand their similarities and differences:

Digital Signature Digital Certificate Comparison Criteria
Purpose A digital signature authenticates the signer claiming to send or create the message or software. A digital certificate is a file in X.509 format that’s typically used on websites to identify the site and establish trust in its users.
Security A digital signature is the actual electronic authentication mechanism that authenticates the signer, assures integrity, and provides non-repudiation. A digital certificate is used to bind the signature to an entity. It provides authentication and security.
Process The message is hashed and encrypted by the signer using a private key before it is sent. The receiver uses the signer’s public key to decrypt and read the message. They can also hash the message again and compare the two hashes to verify message integrity. After the CA conducts its vetting process and issues the certificate, the applicant needs to install it and configure their client or server to enable HTTPS. Once that’s in place, the connection itself is established, starting with an SSL/TLS handshake.

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