> 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/3.hashing/2.hashing-algorithms.md).

# Hashing Algorithms 🛠️

### **MD5 (Message-Digest Algorithm 5)** 📜

* **Introduction**: Developed in the early 1990s, MD5 generates a 128-bit hash digest from 512-bit blocks.
* **Issues**:
  * **Design Flaw**: Discovered in 1996, leading cryptographers to recommend SHA1 as a more secure alternative.
  * **Collision Vulnerability**: By 2004, it was found that MD5 was susceptible to hash collisions, allowing different inputs to produce the same hash.
  * **Exploitation**: In 2008, researchers demonstrated creating a fake SSL certificate using MD5 collisions, leading to serious security breaches like the Flame malware in 2012.
* **Recommendation**: By 2010, it was advised to stop using MD5 for cryptographic applications due to its vulnerabilities.

### **SHA1 (Secure Hash Algorithm 1)** 🔐

* **Introduction**: Part of the Secure Hash Algorithm suite published by NSA in 1995. It generates a 160-bit hash digest from 512-bit blocks.
* **Usage**: Employed in various protocols like TLS/SSL, PGP/SSH, IPSec, and version control systems like Git.
* **Vulnerabilities**:
  * **Weaknesses**: Theoretical attacks were developed in the 2000s, with practical implications emerging in 2015. A full collision attack was estimated to be feasible with significant computing resources.
  * **Full Collision**: In 2017, researchers published the first full SHA1 collision, using substantial CPU and GPU resources equivalent to 6,500 years of a single CPU and 110 years of a single GPU.
* **Recommendation**: SHA1 should be replaced with SHA2 or SHA3 due to its vulnerabilities.

### **Message Integrity Check (MIC) vs. Message Authentication Code (MAC)** 🔍

* **MIC (Message Integrity Check)**:
  * **Function**: A hash digest of a message ensuring that its contents remain unchanged during transit.
  * **Limitations**: Does not use secret keys, hence it does not authenticate the message. It is susceptible to tampering if an attacker can recompute the checksum.
  * **Use Case**: Protects against accidental corruption or loss, but not against intentional modifications.
* **MAC (Message Authentication Code)**:
  * **Function**: Provides both integrity and authentication by using a secret key.

### **Summary** 📜

* **MD5**: Once popular but now obsolete for cryptographic purposes due to serious vulnerabilities and hash collisions.
* **SHA1**: Still used but vulnerable to collisions, and should be replaced by more secure algorithms like SHA2 or SHA3.
* **MIC**: Ensures data integrity but does not offer message authentication.

🔐📉💻

***

## Hashing Algorithms and Security Measures 🔐

### **Authentication and Password Hashing** 🔑

* **Importance of Hashing**:
  * **Why Hash Instead of Plain Text**: Storing passwords in plain text is insecure. If a system is compromised, attackers would gain access to all user passwords.
  * **Hashing Process**: Instead of storing passwords directly, systems store a hash of the password. During login, the entered password is hashed and compared to the stored hash. If they match, authentication is successful.

### **Brute Force Attacks** 🛡️

* **Definition**:
  * An attacker tries all possible input values to find a match for a hashed password.
  * **Computational Intensity**: Brute force attacks are time and resource-intensive. Theoretically, any system can be attacked with unlimited resources, so the goal is to make this process impractically difficult.
* **Mitigation**:
  * **Hashing Iterations**: Increasing the number of times a password is hashed (e.g., thousands of times) makes brute force attacks more difficult and time-consuming.

### **Rainbow Tables** 🌈

* **Definition**:
  * A precomputed table of possible passwords and their corresponding hashes.
  * **Purpose**: Speed up the process of cracking hashed passwords by looking up precomputed values instead of hashing each guess.
* **Protection Against Rainbow Tables**:
  * **Salting**: Adding a unique, random value (salt) to the password before hashing.
    * **How It Works**:
      * A random salt is concatenated with the password and hashed together.
      * The salt is stored along with the hash, making each password hash unique.
    * **Impact**: Attackers would need to generate a separate rainbow table for each possible salt value, making it computationally and storage-wise impractical.
* **Salt Size**:
  * **Early Systems**: Used 12-bit salts (about 4,096 possible values).
  * **Modern Systems**: Use 128-bit salts (over 340 undecillion possible values), raising the difficulty to infeasible levels.

### **Summary** 📜

* **Hashing**: Essential for secure password storage. Avoids storing sensitive data in plain text.
* **Brute Force Attacks**: Difficult to prevent entirely but can be mitigated by increasing the number of hashing iterations.
* **Rainbow Tables**: Precomputed tables of hashes can be defeated by using salts, which make each password hash unique and harder to crack.

🔑🛡️💻