SHA-256
SHA-256 (Secure Hash Algorithm 256-bit) is a cryptographic hash function that belongs to the SHA-2 family, designed by the National Security Agency (NSA) and published by the National Institute of Standards and Technology (NIST) as part of their Federal Information Processing Standards (FIPS) in 2001. Here are key aspects of SHA-256:
Functionality and Design
- Input: SHA-256 can accept an input of any length, padding it if necessary to ensure it is a multiple of 512 bits.
- Output: It produces a 256-bit (32-byte) hash value, commonly rendered as a 64-character hexadecimal number.
- Structure: It uses a Merkle–Damgård construction, where the input message is divided into 512-bit blocks. Each block goes through several rounds of compression functions which involve bitwise operations, modular additions, and logical functions.
Security Properties
- Collision Resistance: It is designed to make finding two different messages with the same hash (a collision) computationally infeasible. The current theoretical attack on SHA-256 would require approximately \(2^{128}\) operations, far beyond current computational capabilities.
- Pre-image Resistance: Given a hash, it should be hard to find any message that produces that hash.
- Second Pre-image Resistance: Given an input, it should be hard to find another input with the same hash.
Applications
- Digital Signatures - Used for ensuring the integrity of documents and software.
- Data Integrity - To verify that data has not been altered.
- Password Hashing - Although not recommended as the sole method for password protection, SHA-256 can be used in conjunction with other techniques.
- Blockchain - SHA-256 is used in Bitcoin for mining and transaction verification.
History
- SHA-256 was introduced as part of the SHA-2 standard in 2001, in response to weaknesses found in the earlier SHA-1 algorithm.
- The development of SHA-2 was motivated by the theoretical vulnerabilities found in SHA-1, including the possibility of finding collisions faster than brute force.
Performance
- SHA-256 is more computationally intensive than SHA-1 but is still considered efficient for many applications, especially where security is paramount.
- On modern hardware, SHA-256 can process data at speeds sufficient for real-time applications.
Current Status
- As of now, SHA-256 remains secure against practical attacks, although there are ongoing efforts to develop even more secure algorithms like those in the SHA-3 family.
- It is widely used and trusted for applications requiring high security.
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