Cryptographic hash function

Cryptographic Hash Function

A cryptographic hash function is a type of hash function that is designed to be a one-way function, meaning it is infeasible to invert or reverse the process. These functions take an input (or 'message') and return a fixed-size string of bytes. The output, typically a 'digest', is unique to each unique input, making cryptographic hash functions a fundamental component in various cryptography applications.

Properties

Cryptographic hash functions have several important properties:

• **Deterministic**: The same input will always produce the same output.
• **Quick Computation**: The hash value is computed quickly.
• **Pre-image Resistance**: Given a hash value, it should be infeasible to find the original input.
• **Small Changes in Input Change the Output**: A small change to the input should produce a significantly different hash.
• **Collision Resistance**: It should be infeasible to find two different inputs that produce the same hash output.
• **Second Pre-image Resistance**: Given an input and its hash, it should be infeasible to find a different input with the same hash.

Applications

Cryptographic hash functions are used in various applications, including:

• **Digital signatures**: Ensuring the integrity and authenticity of a message.
• **Message authentication codes (MACs)**: Verifying the integrity and authenticity of a message.
• **Password hashing**: Storing passwords securely.
• **Data integrity**: Verifying that data has not been altered.
• **Blockchain**: Ensuring the integrity of the blockchain ledger.

Common Cryptographic Hash Functions

Some widely used cryptographic hash functions include:

• MD5
• SHA-1
• SHA-2
• SHA-3
• RIPEMD

Security Considerations

The security of a cryptographic hash function is critical. Weaknesses in hash functions can lead to vulnerabilities in the systems that rely on them. For example, the discovery of collisions in MD5 and SHA-1 has led to their deprecation in favor of more secure algorithms like SHA-2 and SHA-3.

See Also

• Hash function
• Cryptography
• Digital signature
• Message authentication code
• Password hashing
• Data integrity
• Blockchain

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