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TLS/SSL Certificate

Other names:

  • SSL Certificate
  • TSL Certificate
  • TLS/SSL server certificate

What is an SSL/TLS Certificate?

Definition: An SSL (Secure Sockets Layer) or TLS (Transport Layer Security) certificate is a digital certificate that authenticates the identity of a website and enables an encrypted connection between the web server and the user's browser.

Purpose: Certificates ensure that data transmitted between the user and the server is secure and that the website is genuine, helping to establish trust.

How SSL Certificates work

Step 1: Certificate Issuance

  1. Certificate Signing Request (CSR):
    • The website owner generates a CSR, which includes the public key and information about the organization (e.g., domain name, organization name).
    • This CSR is sent to a Certificate Authority (CA) to request an SSL certificate.
  2. Validation:
    • The CA verifies the information provided in the CSR. Depending on the type of certificate (Domain Validation, Organization Validation, or Extended Validation), this process may vary in complexity.
  3. Certificate Issuance:
    • Once validated, the CA issues the SSL certificate, which includes the website's public key, information about the issuer, the validity period, and the digital signature of the CA.

Step 2: SSL Handshake

  1. Client Connection:
    • When a user accesses a website (e.g., https://www.example.com), the browser initiates a connection to the server.
  2. Server Response:
    • The server responds by sending its SSL certificate to the browser.
  3. Validation by Client:
    • The browser checks the certificate:
      • It verifies the certificate's validity period.
      • It checks that the certificate is issued by a trusted CA.
      • It ensures that the domain name matches the one in the certificate.
  4. Public Key Exchange:
    • If the certificate is valid, the browser uses the public key from the certificate to encrypt a randomly generated session key.
  5. Session Key Establishment:
    • The encrypted session key is sent to the server, which uses its private key to decrypt it. Now both the server and client share a session key for symmetric encryption.

Step 3: Encrypted Communication

  • With the session key established, all subsequent data transmitted between the client and server is encrypted using this symmetric key, ensuring confidentiality and integrity.

Connection to Routing

  • Secure Routing: When a user enters a URL starting with https://, the browser requests a secure connection to the server. The server presents its SSL/TLS certificate during the connection process.
  • SSL Handshake: This process involves the browser and server exchanging cryptographic keys to establish a secure session. The certificate is used to authenticate the server's identity, ensuring that the user is connecting to the intended website and not an imposter.
  • Trust Chain: Certificates are issued by trusted certificate authorities (CAs). Browsers come preloaded with a list of trusted CAs. If the certificate is valid and signed by a trusted CA, the browser establishes a secure connection.

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