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SSL/TLS

SSL (Secure Sockets Layer) and TLS (Transport Layer Security) are cryptographic protocols designed to provide secure communication over a computer network, most commonly the internet. They ensure that data transmitted between a client (e.g., a web browser) and a server (e.g., a website) is encrypted and secure from eavesdropping, tampering, or forgery.

  • SSL: The older protocol, now deprecated due to security vulnerabilities.

  • TLS: The modern, more secure version that has replaced SSL. Despite the name change, many people still refer to TLS as SSL.

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How SSL/TLS Works

SSL/TLS works by establishing an encrypted connection between the client and server. This process involves several steps:

1. Handshake Protocol

  • The client and server agree on the version of SSL/TLS to use.

  • The server sends its digital certificate (containing its public key) to the client.

  • The client verifies the certificate with a trusted Certificate Authority (CA).

  • The client and server generate a shared symmetric key (session key) for encryption.

2. Key Exchange

  • The client encrypts a pre-master secret with the server's public key and sends it to the server.

  • Both the client and server use this pre-master secret to generate the same symmetric session key.

3. Encrypted Communication

  • Once the session key is established, all data exchanged between the client and server is encrypted using this key.

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Key Components of SSL/TLS

  1. Encryption:

    • SSL/TLS uses both symmetric encryption (for speed) and asymmetric encryption (for secure key exchange).

    • Symmetric encryption uses the same key for both encryption and decryption.

    • Asymmetric encryption uses a public key for encryption and a private key for decryption.

  2. Digital Certificates:

    • A digital certificate is issued by a trusted Certificate Authority (CA).

    • It contains the server's public key, domain name, and the CA's digital signature.

    • Examples of CAs: Let's Encrypt, DigiCert, Comodo.

  3. Cipher Suites:

    • A combination of algorithms used for encryption, key exchange, and message authentication.

    • Example: TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256.

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SSL/TLS in HTTPS

HTTPS (Hypertext Transfer Protocol Secure) is HTTP over SSL/TLS. When you visit a website using HTTPS, the following happens:

  1. The browser connects to the server using HTTPS (port 443).

  2. The server presents its SSL/TLS certificate.

  3. The browser verifies the certificate.

  4. An encrypted connection is established, and data is transmitted securely.

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Example of SSL/TLS in Action

  1. Client Hello:

    • The client sends a "Client Hello" message to the server, specifying the SSL/TLS version and supported cipher suites.

  2. Server Hello:

    • The server responds with a "Server Hello" message, selecting the SSL/TLS version and cipher suite.

  3. Certificate Exchange:

    • The server sends its digital certificate to the client.

  4. Key Exchange:

    • The client and server exchange keys to establish a secure session.

  5. Encrypted Communication:

    • Data is encrypted and transmitted securely.

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Benefits of SSL/TLS

  1. Data Encryption:

    • Protects sensitive information (e.g., passwords, credit card numbers) from being intercepted.

  2. Data Integrity:

    • Ensures that data is not tampered with during transmission.

  3. Authentication:

    • Verifies the identity of the server (and optionally the client).

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SSL vs. TLS

Feature
SSL
TLS

Versions

SSL 2.0, SSL 3.0

TLS 1.0, TLS 1.1, TLS 1.2, TLS 1.3

Security

Less secure (deprecated)

More secure

Encryption

Uses older encryption algorithms

Uses modern, stronger algorithms

Adoption

No longer used

Widely used

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Example of TLS 1.3 Handshake

  1. Client Hello:

    • Client sends supported TLS version, cipher suites, and a random number.

  2. Server Hello:

    • Server selects TLS version, cipher suite, and sends its certificate and a random number.

  3. Key Exchange:

    • Client and server exchange keys to establish a shared secret.

  4. Finished:

    • Both parties verify the handshake and begin encrypted communication.

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Summary

  • SSL/TLS ensures secure communication over the internet by encrypting data and verifying identities.

  • TLS is the modern, secure replacement for SSL.

  • HTTPS uses SSL/TLS to secure HTTP traffic.

  • SSL/TLS provides encryption, data integrity, and authentication, making it essential for secure web communication.

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