SSL (now more commonly TLS) ensures secure communication between your browser and a web server through a series of steps involving certificate verification and encryption. Here's a breakdown of the process:
1. Connection Request
When you type a website address that starts with "https://" (indicating SSL/TLS is in use) into your browser, or when your browser encounters an https link, it initiates a secure connection to the web server.
2. Server Identification and Certificate Presentation
The browser requests that the web server identify itself. The server responds by sending a copy of its SSL/TLS certificate to the browser. This certificate contains information about the server's identity, including its domain name and the certificate authority (CA) that issued the certificate.
3. Certificate Validation
The browser performs several checks to determine if it trusts the SSL/TLS certificate:
- Certificate Authority (CA) Trust: The browser checks if the certificate was issued by a trusted CA. Browsers maintain a list of trusted CAs. If the CA is not on this list, the browser will display a warning.
- Validity Period: The browser verifies that the certificate is still within its validity period (i.e., not expired or not yet valid).
- Domain Name Verification: The browser checks if the domain name in the certificate matches the domain name of the website you are trying to access. This prevents man-in-the-middle attacks.
- Revocation Status (Optional): Browsers can optionally check the certificate's revocation status using protocols like OCSP (Online Certificate Status Protocol) or CRL (Certificate Revocation List) to ensure the certificate hasn't been revoked due to compromise.
4. Key Exchange and Secure Communication
If the certificate is valid, the browser and server negotiate a symmetric encryption algorithm and session keys using asymmetric encryption (public/private key cryptography). The server's public key, which is included in the SSL/TLS certificate, is used for this initial secure key exchange.
5. Encrypted Data Transfer
Once the secure connection is established, all data transmitted between the browser and the server is encrypted using the agreed-upon symmetric encryption algorithm and session keys. This prevents eavesdropping and tampering by third parties.
Visual Summary
| Step | Action | Purpose |
|---|---|---|
| 1. Connection Request | Browser requests a secure connection to the web server. | Initiates the secure communication process. |
| 2. Certificate Presentation | Server sends its SSL/TLS certificate to the browser. | Provides the browser with the server's identity and public key. |
| 3. Certificate Validation | Browser verifies the certificate's authenticity and validity. | Ensures the server is who it claims to be and prevents fraudulent certificates. |
| 4. Key Exchange | Browser and server negotiate encryption algorithms and session keys. | Establishes a secure channel for encrypted communication. |
| 5. Encrypted Data Transfer | All data transmitted between the browser and server is encrypted. | Protects sensitive information from eavesdropping and tampering. |
In essence, SSL/TLS in a browser ensures a secure, encrypted connection, verifying the website's identity and protecting your data.
