Software-Engineering

TLS/SSL Protocols

What is SSL/TLS?

SSL (Secure Sockets Layer) and TLS (Transport Layer Security) are cryptographic protocols that provide secure communication over computer networks. TLS is the successor to SSL and is widely used to secure web traffic (HTTPS), email, VoIP, and other communications.

SSL vs TLS

• SSL: Developed by Netscape in 1995, deprecated due to vulnerabilities
• TLS: IETF standardization of SSL, backward compatible
• Current Standard: TLS 1.3 (RFC 8446, 2018)

Why is TLS Needed?

TLS addresses fundamental security requirements:

• Confidentiality: Protects data from eavesdropping
• Integrity: Ensures data hasn’t been modified
• Authentication: Verifies identity of communicating parties
• Non-repudiation: Prevents denial of actions

Without TLS, network communications are vulnerable to:

• Man-in-the-middle attacks
• Data interception
• Tampering
• Impersonation

How Does TLS Work?

TLS operates as a sublayer between application protocols (HTTP, SMTP) and transport protocols (TCP). It provides:

1. Encryption: Symmetric cryptography for data protection
2. Authentication: Digital certificates for identity verification
3. Integrity: Message authentication codes (MAC) for tamper detection

TLS Handshake Process

The TLS handshake establishes a secure connection:

sequenceDiagram
    participant Client
    participant Server

    Client->>Server: Client Hello<br/>(TLS version, cipher suites, random)
    Server->>Client: Server Hello<br/>(chosen cipher, random, session ID)
    Server->>Client: Certificate<br/>(server's public key certificate)
    Server->>Client: Server Key Exchange<br/>(if needed for key exchange)
    Server->>Client: Certificate Request<br/>(if client auth required)
    Server->>Client: Server Hello Done
    Client->>Server: Certificate<br/>(client cert if requested)
    Client->>Server: Client Key Exchange<br/>(pre-master secret encrypted with server's public key)
    Client->>Server: Certificate Verify<br/>(if client cert sent)
    Client->>Server: Change Cipher Spec
    Client->>Server: Finished<br/>(verify handshake integrity)
    Server->>Client: Change Cipher Spec
    Server->>Client: Finished

Handshake Steps Explained

1. Client Hello: Client proposes TLS version and cipher suites
2. Server Hello: Server selects protocol parameters
3. Certificate: Server sends its certificate for authentication
4. Key Exchange: Parties exchange information to generate session keys
5. Change Cipher Spec: Switch to encrypted communication
6. Finished: Verify handshake was not tampered with

Cryptographic Primitives

Symmetric Encryption

• Used for bulk data encryption after handshake
• Fast, efficient for large data volumes
• Examples: AES-128-GCM, ChaCha20-Poly1305

Asymmetric Encryption

• Used during handshake for key exchange
• Slower, used for small amounts of data
• Examples: RSA, ECDHE (Elliptic Curve Diffie-Hellman)

Hash Functions

• Provide integrity and generate MACs
• Examples: SHA-256, SHA-384

Digital Signatures

• Verify authenticity of certificates
• Examples: RSA signatures, ECDSA

TLS Versions

SSL 1.0 (1995)

• Never publicly released due to security flaws

SSL 2.0 (1995)

• Initial public version
• Vulnerable to man-in-the-middle attacks
• Deprecated in 2011

SSL 3.0 (1996)

• Improved security over SSL 2.0
• Vulnerable to POODLE attack
• Deprecated in 2015

TLS 1.0 (1999)

• First TLS version
• Vulnerable to BEAST attack
• Deprecated in 2020

TLS 1.1 (2006)

• Protection against CBC attacks
• Still vulnerable to some attacks

TLS 1.2 (2008)

• Widely used, considered secure with proper ciphers
• Supports modern cipher suites
• Still current for many applications

TLS 1.3 (2018)

• Major overhaul for better security and performance
• 1-RTT handshake (vs 2-RTT in 1.2)
• Perfect forward secrecy by default
• Removed vulnerable cipher suites

Common TLS Attacks and Mitigations

Attack	Description	Mitigation
POODLE	SSL 3.0 padding oracle	Disable SSL 3.0
BEAST	CBC mode attack	Use TLS 1.1+ or AEAD ciphers
Heartbleed	OpenSSL buffer overflow	Update OpenSSL, use TLS 1.2+
Logjam	Weak DH parameters	Use strong DH parameters
FREAK	RSA export cipher suites	Disable export ciphers
DROWN	Cross-protocol attack	Disable SSL/TLS on same server