What is Transport Layer Security?

What is TLS?

Transport Layer Security (TLS) is a cryptographic protocol that provides secure communication over a computer network, most commonly the internet. TLS encrypts data exchanged between client and server systems — such as a web browser and a website — ensuring that the data remains private and unaltered in transit.

TLS is the successor to SSL (Secure Sockets Layer) and is widely used to secure applications like HTTPS websites, email, instant messaging, and VoIP services.

TSL vs. SSL

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Although "SSL" is still commonly referenced, nearly all secure internet communication today uses TLS, not SSL.

Why TLS Matters

1. Protects privacy: TLS encrypts data to prevent unauthorized access or surveillance.
2. Authenticates identities: Ensures that the server (and sometimes the client) is who it claims to be via certificates.
3. Preserves data integrity: Prevents tampering or alteration of data during transmission.
4. Builds user trust: Enables HTTPS, which displays a padlock in browsers to signal secure connections.
5. Supports compliance: TLS is a requirement for standards like PCI-DSS, HIPAA, and GDPR.

TLS is essential for protecting sensitive data across public and private networks.

How TLS Works

1. Handshake Phase
   
   • The client and server agree on encryption methods (cipher suites).
   • The server presents its TLS certificate, which is verified by the client.
   • A session key is securely exchanged using asymmetric cryptography.
2. Data Encryption Phase
   
   • Once the handshake is complete, symmetric encryption is used to protect data during the session.
3. Session Integrity
   
   • TLS uses message authentication codes (MACs) to ensure that transmitted data isn’t altered.

Common TLS Use Cases

• HTTPS websites: Secure online transactions, logins, and personal data.
• Email servers (SMTP, IMAP, POP3): Protects email in transit.
• VPNs and remote access: Secures connections over public networks.
• APIs and microservices: Ensures secure communication between services.
• VoIP and chat apps: Encrypts voice and messaging data.

TLS Versions

• TLS 1.0 and 1.1: Deprecated due to weak encryption.
• TLS 1.2: Most widely used version today.
• TLS 1.3: Faster, more secure, and removes outdated cryptographic functions.

Organizations should disable older versions and enforce TLS 1.2+ to maintain strong security postures.

FAQs

1. Is TLS the same as HTTPS?

Not exactly. HTTPS is HTTP over TLS. TLS provides the encryption layer that secures HTTP connections.

2. What’s the difference between TLS and SSL?

TLS is the modern, more secure evolution of SSL. SSL is outdated and should no longer be used.

3. How can I tell if a site uses TLS?

Look for “https://” in the URL and a padlock icon in the browser’s address bar.

4. Can TLS stop all attacks?

No. TLS encrypts data in transit but doesn’t prevent endpoint or application-layer attacks. It’s one layer in a defense-in-depth strategy.

How Illumio Supports TLS-Based Security

While TLS secures data in transit, it doesn't address lateral movement or insider threats within an organization’s internal network. Illumio complements TLS by visualizing and segmenting application traffic to prevent unauthorized access, even between trusted systems. With Illumio, you can see and control how services communicate across environments, strengthening your defense beyond perimeter encryption.

Summary

Transport Layer Security (TLS) is the foundation of secure communication on the internet. By encrypting data, authenticating servers, and verifying message integrity, TLS protects users and systems from eavesdropping, tampering, and impersonation. It’s a critical component of modern cybersecurity, but not the only one. 

Organizations should pair TLS with endpoint protection, segmentation, and layered defenses for end-to-end security. Read more on Illumio Segmentation to get end-to-end security for your organization.