> For the complete documentation index, see [llms.txt](https://chunhthanhde.gitbook.io/google-learning-programs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://chunhthanhde.gitbook.io/google-learning-programs/google-it-support-professional-certificate/course-5-it-security-defense-against-the-digital-dark-arts/module-2-pelcgbybtl-cryptology/4.cryptography-applications/3.cryptography-in-action.md).

# Cryptography in Action 🔒💻

## **HTTPS and TLS** 🌐🔐

* **HTTPS**:
  * Secure version of HTTP (Hypertext Transfer Protocol).
  * Utilizes SSL (Secure Sockets Layer) or TLS (Transport Layer Security) to encrypt HTTP traffic.
  * Ensures encrypted communication over the internet, protecting data from eavesdroppers, verifying both parties, and maintaining data integrity.
* **TLS**:
  * A protocol for secure communications beyond just web browsing (e.g., VoIP calls, email, instant messaging, Wi-Fi security).
  * **Functions**:
    1. **Secure Communication**: Protects data from potential eavesdroppers.
    2. **Authentication**: Verifies the identity of communicating parties (typically the server to the client).
    3. **Integrity**: Ensures messages are not lost or altered in transit.
* **TLS Handshake**:
  * **ClientHello**: Client initiates connection with supported TLS version and cipher suites.
  * **ServerHello**: Server responds with selected protocol version and cipher suite, transmits its digital certificate.
  * **Certificate Validation**: Client checks the server's certificate for validity and hostname.
  * **ClientKeyExchange**: Establishes a shared secret for symmetric encryption.
  * **ChangeCipherSpec**: Signals the switch to secure communication.
  * **Finished Messages**: Verifies successful completion of the handshake and secure channel establishment.
* **Forward Secrecy**:
  * Ensures session keys remain secure even if private keys are compromised.

## **SSH (Secure Shell)** 🔐🖥️

* **Overview**:
  * Secure network protocol for accessing network services over unsecured networks.
  * Commonly used for remote command-line login.
  * Replaces unsecured protocols like Telnet, rlogin, and rexec.
* **Features**:
  * Uses public key cryptography for remote machine authentication.
  * Supports various key exchange mechanisms and symmetric encryption ciphers.
  * Can tunnel arbitrary network ports and traffic over the encrypted channel.
* **Public Key Authentication**:
  * User generates a key pair, distributing the public key to systems for authentication.
  * SSH verifies the public key against the private key, which remains secure with the user.

## **PGP (Pretty Good Privacy)** 📧🔐

* **Overview**:
  * An encryption application for authenticating data and ensuring privacy.
  * Commonly used for encrypted email, disk encryption, and file protection.
  * Developed by Phil Zimmermann in 1991 as a tool for secure communications among activists.
* **Historical Context**:
  * Faced legal challenges due to U.S. export restrictions on encryption technology.
  * Zimmermann creatively challenged restrictions by publishing the source code in a printed book, protected by the First Amendment.
  * Investigation closed in 1996 without charges.
* **Security**:
  * Highly secure, comparable to military-grade encryption.
  * Historically used RSA algorithm, later replaced by DSA to avoid licensing issues.

🔒🗝️


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