Secure Socket Layer (SSL) (original) (raw)

Last Updated : 28 Apr, 2026

Secure Sockets Layer (SSL) is an Internet security protocol that encrypts data to ensure secure communication between devices over a network.

Developed by Netscape in 1995, SSL provides privacy, authentication and data integrity for online communications.
It is the predecessor of TLS (Transport Layer Security), which is now the standard protocol for secure communications on the Internet.

handshake_protocol

Secure Socket Layer (SSL)

**Note: Websites using SSL/TLS display "HTTPS" in their URLs instead of "HTTP," indicating that communications are encrypted and secure.

Working of SSL

SSL ensures secure communication through three main mechanisms:

**Encryption: Data transmitted over the network is encrypted, preventing unauthorized parties from reading it. If intercepted, encrypted data appears as an unreadable jumble of characters.
**Authentication: SSL uses a handshake process to authenticate both the client and server, ensuring each party is legitimate and not an imposter.
**Data Integrity: SSL digitally signs transmitted data to detect any tampering, ensuring that the data received is exactly what was sent.

Before SSL, web data was transmitted in plaintext, making it vulnerable to interception. SSL solves this by:

Encrypting sensitive information such as login credentials, financial transactions and personal data.
Authenticating web servers to prevent users from connecting to fraudulent websites.
Ensuring data integrity so transmitted information cannot be modified during transit.

**Note: SSL protects against cyber threats by providing confidentiality, authentication and integrity for online communications.

SSL consists of several protocols, each handling a different aspect of secure communication

application_data

SSL Record Protocol

Provides confidentiality and message integrity.
Application data is divided into fragments, optionally compressed and appended with a Message Authentication Code (MAC).
The data is then encrypted and transmitted with an SSL header.

Establishes SSL sessions and authenticates clients and servers.

ssl_handshake_protocol

SSL Handshake Protocol Phases diagrammatic representation

**Four phases:

1_byte

Change Cipher Spec Protocol

Signals that pending cryptographic parameters from the handshake should now become active.
Consists of a single 1-byte message.

level_

Alert Protocol

Communicates SSL-related warnings or errors.
**Warning alerts (level 1): Non-critical issues, such as expired or unsupported certificates.
**Fatal alerts (level 2): Critical errors, such as handshake failures, bad record MAC or illegal parameters, which terminate the connection.

Version	Release Year	Notes
SSL 1	Never released	Insecure
SSL 2	1995	First public release
SSL 3	1996	Improved security
TLS 1.0	1999	Successor to SSL 3.0
TLS 1.1	2006	Improved encryption and security
TLS 1.2	2008	Widely adopted, strong encryption
TLS 1.3	2018	Modern, efficient, secure protocol

**Note: Today, TLS has replaced SSL, but the term "SSL" is still commonly used.

SSL certificates are digital certificates issued by trusted Certificate Authorities (CAs) to secure and verify websites.

**Encryption: Protects sensitive information during transmission.
**Authentication: Confirms the identity of the website or service.
**Integrity: Ensures transmitted data is not altered.
**Non-repudiation: Prevents denial of transmitted messages.
**Public-key cryptography: Facilitates secure key exchange.
**Session management: Allows resumption of secure sessions after interruptions.

**Domain Validation (DV): Confirms domain ownership.
**Organization Validation (OV): Confirms the organization's identity.
**Extended Validation (EV): Rigorous verification, highest trust level, often indicated by a green address bar.

**SSL: Older protocol, no longer considered secure.
**TLS: Updated and more secure version of SSL.
Despite TLS being the standard, the term "SSL" is still widely used in marketing and casual references.