Key Stretching

From binaryoption
Jump to navigation Jump to search
Баннер1
  1. Key Stretching

Key stretching is a fundamental security practice used in cryptography and information security to protect passwords and other sensitive data. It is a process of repeatedly applying a one-way function, such as a cryptographic hash function, to a password (or key) along with a salt. This transforms the password into a longer, more complex representation, making it significantly harder for attackers to crack through methods like brute-force attacks, rainbow table attacks, and dictionary attacks. This article details the concepts behind key stretching, its importance, common algorithms, and practical considerations for implementation.

The Problem: Why Simple Hashing Isn't Enough

Traditionally, storing passwords involved simply hashing them. A hash function takes an input (the password) and produces a fixed-size output (the hash). The hash is then stored, not the password itself. When a user tries to log in, the entered password is hashed, and the resulting hash is compared to the stored hash. If they match, the authentication succeeds.

However, this approach has several weaknesses:

  • **Speed of Hashing:** Modern computing power allows attackers to rapidly compute hashes for a massive number of passwords. If an attacker gains access to the database of stored hashes, they can quickly try to find matches for common passwords.
  • **Rainbow Tables:** Rainbow tables are precomputed tables of hashes for a large set of passwords. Attackers can use these tables to quickly reverse the hashing process and identify the original passwords.
  • **Dictionary Attacks:** Attackers can hash words from a dictionary and compare them to the stored hashes.
  • **Brute-Force Attacks:** Attackers can systematically try all possible combinations of characters until a match is found.

The speed at which these attacks can be performed is a critical flaw. A weak password can be cracked in seconds, even minutes.

How Key Stretching Works

Key stretching addresses these vulnerabilities by intentionally *slowing down* the hashing process. Instead of hashing the password once, key stretching algorithms repeat the hashing process many times (thousands or even millions), making it computationally expensive for attackers.

The basic process involves:

1. **Salt Generation:** A random string called a salt is generated for each password. The salt is unique for each user and is stored alongside the stretched hash. The salt prevents rainbow table attacks because each password will have a different salt, resulting in a different hash even if the passwords are the same. A unique salt for each password is crucial; using the same salt for all users defeats the purpose. 2. **Combining Password and Salt:** The password and salt are combined (often by concatenation). 3. **Iterative Hashing:** The combined password and salt are fed into a hash function repeatedly. The number of iterations is a configurable parameter, often referred to as the cost factor or work factor. Higher cost factors increase security but also increase the time required for authentication. 4. **Storing the Stretched Hash and Salt:** The final stretched hash and the salt are stored in the database.

During authentication, the same process is repeated – the entered password is combined with the stored salt, iteratively hashed with the same cost factor, and the result is compared to the stored stretched hash.

Key Stretching Algorithms

Several key stretching algorithms are commonly used. Here are some of the most prominent:

  • **PBKDF2 (Password-Based Key Derivation Function 2):** PBKDF2 is a widely used and well-respected algorithm defined in RFC 6070. It applies a pseudorandom function (PRF), typically HMAC-SHA256, to the password and salt repeatedly. It allows for specifying the iteration count, salt length, and desired key length. It’s considered a strong algorithm, especially with a sufficiently high iteration count. Cryptographic hash function selection significantly impacts the security.
  • **bcrypt:** bcrypt is another popular algorithm specifically designed for password hashing. It incorporates a work factor that automatically adjusts the hashing time based on the available computing power. This makes it resistant to attacks even as hardware improves. bcrypt is known for its robustness and is often recommended. Security best practices often include bcrypt.
  • **scrypt:** scrypt is a key derivation function that is designed to be resistant to both CPU and GPU-based attacks. It requires a large amount of memory, making it more difficult and expensive for attackers to parallelize the cracking process. scrypt is considered very secure but can be more resource-intensive than PBKDF2 or bcrypt. Computational complexity is a key consideration.
  • **Argon2:** Argon2 is a modern key derivation function that won the Password Hashing Competition in 2015. It offers three variants (Argon2d, Argon2i, and Argon2id), each optimized for different attack scenarios. Argon2 is highly configurable and provides excellent security. Password Hashing Competition results highlighted Argon2's strengths.

Choosing the Right Algorithm and Parameters

Selecting the appropriate key stretching algorithm and parameters is crucial. Here's a breakdown of considerations:

  • **Algorithm Choice:** Argon2 is generally considered the most secure option currently available. bcrypt is a strong and well-established alternative. PBKDF2 is still acceptable if implemented with a sufficiently high iteration count. scrypt is a viable option, but its memory requirements may be a concern.
  • **Iteration Count/Work Factor:** This parameter determines the computational cost of key stretching. A higher value increases security but also increases authentication time. The ideal value depends on the available hardware and the desired level of security. Regularly reassess and increase the iteration count as computing power increases.
  • **Salt Length:** The salt should be at least 16 bytes (128 bits) long and generated using a cryptographically secure random number generator. Longer salts provide better protection against rainbow table attacks. Random Number Generation is critical for salt creation.
  • **Hash Length:** The length of the resulting hash should be sufficient to prevent collisions. A hash length of at least 256 bits is recommended.
  • **Memory Usage (for scrypt and Argon2):** scrypt and Argon2 require a significant amount of memory. Ensure that your system has enough memory to handle the chosen parameters.

Implementation Considerations

  • **Use Established Libraries:** Do not attempt to implement key stretching algorithms yourself. Use well-vetted and maintained libraries provided by your programming language or framework. These libraries handle the complexities of the algorithms correctly and are less prone to vulnerabilities. Software libraries are essential for secure implementation.
  • **Secure Random Number Generator:** Use a cryptographically secure random number generator to generate salts. Avoid using pseudo-random number generators that are not suitable for security-sensitive applications.
  • **Storage Security:** Protect the stored stretched hashes and salts from unauthorized access. Ensure that your database is properly secured and that access controls are in place.
  • **Regular Updates:** Stay up-to-date with the latest security recommendations and update your key stretching algorithms and parameters as needed. As computing power increases, you may need to increase the iteration count or switch to a more secure algorithm.
  • **Error Handling:** Implement robust error handling to prevent information leakage. Avoid displaying detailed error messages to users that could reveal information about the hashing process.
  • **Database Design**: Efficiently storing salts and stretched hashes is important for performance. Consider using appropriate data types and indexing strategies. Database optimization can improve application speed.

Common Mistakes to Avoid

  • **Using Weak Salts:** Using short or predictable salts makes the system vulnerable to attack.
  • **Using Low Iteration Counts:** A low iteration count provides insufficient protection against brute-force attacks.
  • **Implementing Algorithms Incorrectly:** Incorrectly implementing key stretching algorithms can introduce vulnerabilities.
  • **Storing Passwords in Plain Text:** Never store passwords in plain text.
  • **Using the Same Salt for All Users:** Using the same salt defeats the purpose of salting.
  • **Ignoring Updates:** Failing to update algorithms and parameters as computing power increases.
  • **Insufficient Entropy for Salt Generation:** Using a weak random number generator for salt creation.
  • **Not Protecting Stored Hashes and Salts:** Leaving sensitive data exposed to unauthorized access.
  • **Relying on Custom Implementations:** Using untested or poorly reviewed code instead of established libraries.

Relationship to Other Security Concepts

Key stretching is closely related to several other security concepts:

  • **Authentication**: Key stretching is a crucial component of secure authentication systems.
  • **Authorization**: While key stretching protects the password itself, authorization determines what resources a user has access to after successful authentication.
  • **Cryptography**: Key stretching relies on cryptographic hash functions and other cryptographic principles.
  • **Data Security**: Protecting passwords is a critical aspect of overall data security.
  • **Security Auditing**: Regularly auditing your key stretching implementation can help identify and address vulnerabilities.
  • **Two-Factor Authentication**: Combining key stretching with two-factor authentication provides an even higher level of security.
  • **Least Privilege**: Ensuring that only authorized personnel have access to sensitive data, including stored hashes and salts.
  • **Defense in Depth**: Implementing multiple layers of security, including key stretching, to protect against various types of attacks.
  • **Penetration Testing**: Regularly conducting penetration tests can help identify vulnerabilities in your key stretching implementation.
  • **Vulnerability Management**: Proactively identifying and addressing vulnerabilities in your system.

Advanced Topics

  • **Adaptive Hashing:** Algorithms like bcrypt and Argon2 automatically adjust the work factor based on the available computing power.
  • **Hardware Acceleration:** Some key stretching algorithms can be accelerated using specialized hardware.
  • **Side-Channel Attacks:** These attacks attempt to extract information about the password by analyzing the timing or power consumption of the hashing process.
  • **Homomorphic Encryption:** While not directly related to key stretching, homomorphic encryption allows computations to be performed on encrypted data without decrypting it, offering a potential future direction for password security.
  • **Post-Quantum Cryptography:** As quantum computers develop, existing cryptographic algorithms may become vulnerable. Research into post-quantum cryptography is ongoing, and future key stretching algorithms may need to incorporate post-quantum resistant hash functions.

Resources and Further Reading

Hashing, Salting, Password Security, Data Encryption, Cryptographic Algorithms, Authentication Methods, Security Protocols, Cybersecurity, Information Security, Network Security

Start Trading Now

Sign up at IQ Option (Minimum deposit $10) Open an account at Pocket Option (Minimum deposit $5)

Join Our Community

Subscribe to our Telegram channel @strategybin to receive: ✓ Daily trading signals ✓ Exclusive strategy analysis ✓ Market trend alerts ✓ Educational materials for beginners

Баннер
Retrieved from "https://binaryoption.wiki/index.php?title=Key_Stretching&oldid=44568"