Hashing
Hashing Algorithms
Hashing algorithms take an input (or 'message') and produce a fixed-length string of characters, which is typically a digest that is unique (within reason) to each unique input. A good hash function makes it hard to find two different inputs that produce the same output.
Key Properties of Cryptographic Hash Functions:
Deterministic: For a given input, the output (hash) will always be the same.
Fast to compute: For any given input, the computation of the hash value should be quick.
Pre-image resistant: Given a hash, it should be computationally infeasible to find an input that hashes to that value.
Small changes in input produce drastic changes in output: Even a single-bit change in input should produce an entirely different hash.
Collision resistant: It should be computationally infeasible to find two different inputs that produce the same hash.
Fixed-size output: Regardless of the length of the input, the hash value should be of a fixed length.
Common Hashing Algorithms:
MD5 (Message Digest Algorithm 5):
Output Size: 128 bits
Status: Unsafe. Vulnerable to collision attacks.
Usage: Initially used for integrity checking, password storage, and more.
Issues: Multiple vulnerabilities discovered, making it unsuitable for further use.
SHA-1 (Secure Hash Algorithm 1):
Output Size: 160 bits
Status: Unsafe. Vulnerable to collision attacks.
Usage: Used in digital signatures, certificates, and more.
Issues: Cryptanalysts have found collision cases for SHA-1, making it unsuitable for cryptographic security.
SHA-256/SHA-3 (part of SHA-2 and SHA-3 families):
Output Size: 256 bits (can vary for different SHA-2 functions like SHA-512)
Status: Safe (as of current knowledge).
Usage: Used in many security certificates and encryption technologies. Bitcoin's proof-of-work consensus algorithm also uses SHA-256.
Features: SHA-2 is a family of functions (like SHA-224, SHA-256, SHA-384, SHA-512). SHA-3 is the latest member of the Secure Hash Algorithm family, designed to provide a higher security level.
bcrypt:
Purpose: Password hashing.
Status: Safe (as of current knowledge).
Features: Incorporates a salt to protect against rainbow table attacks. Adaptive over time (work factor can be increased as hardware gets faster).
scrypt:
Purpose: Password hashing.
Status: Safe (as of current knowledge).
Features: Designed to be memory-hard to make brute-force attacks using custom hardware much more difficult.
Argon2:
Purpose: Password hashing.
Status: Safe (as of current knowledge). Winner of the Password Hashing Competition in 2015.
Features: Provides resistance against GPU-based attacks, optimizing for multiple cores and even using a level of threading.
Recommendations and Best Practices:
Avoid MD5 and SHA-1: Due to their vulnerabilities, they should not be used for cryptographic purposes.
Prefer SHA-2 or SHA-3 for General Hashing: For tasks requiring cryptographic hashing (but not password hashing), SHA-256 (or another member of the SHA-2 family) is currently recommended.
Use Password-Specific Hash Functions: For hashing passwords, prefer bcrypt, scrypt, or Argon2. They're designed to be slow and incorporate features like salting to counteract the typical ways attackers crack passwords.
Use Salts: Always use a unique salt for hash computations, especially for passwords, to prevent pre-computed 'rainbow table' attacks.
Regularly Update and Migrate: Cryptography is an evolving field. Regularly review and update cryptographic practices. If an algorithm starts showing signs of weakness, migrate to a stronger one.
Conclusion:
Hashing is a foundational concept in cryptography, ensuring data integrity and serving as a building block for many other cryptographic techniques. Given the evolving landscape, with researchers continually analyzing and finding weaknesses in algorithms, it's imperative to stay updated and use algorithms that are currently considered secure.
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