🔑Hashing

NEW

Also known as: Data Encoding

Transforming input data to a fixed-size output using a deterministic algorithm, often for indexing, integrity, or security.

DESCRIPTION

Hashing applies a deterministic function to map arbitrary-length input to a fixed-size digest. Cryptographic hashes (e.g., SHA-256) are designed to be collision-resistant and preimage-resistant. Non-cryptographic hashes power hash tables and partitioning. Use cases include integrity checks, deduplication, password storage (with salting and key stretching), and load balancing via consistent hashing. Selection must align with security and performance needs.

ALTERNATIVE DEFINITIONS

NIST

A function that maps a bit string of arbitrary length to a fixed-length bit string.

Concise formal definition of a hash function’s mapping.

Source

Wikipedia

A hash function is any function that can be used to map data of arbitrary size to fixed-size values.

General-purpose definition across contexts.

Source

Cloudflare

A cryptographic hash function takes an input and returns a fixed-size string of bytes. The output is typically a ‘digest’ that is unique to each unique input.

Focuses on cryptographic properties and uniqueness expectations.

Source

RELATED TERMS

Hash Table Cryptographic Hash SHA-256 MD5 Checksum Salting Bloom Filter Fingerprint Consistent Hashing

COMPETING TERMS

Data Encryption

RELATIONS

• Narrower: Consistent Hashing Feature Hashing Locality-Sensitive Hashing NTLM Windows Hashing Password Hashing

KNOWLEDGE AREAS

Data Security Data Engineering Mathematics Software Engineering Data Storage & Operations

TARGET AUDIENCE

Software Developer Data Engineer DevOps Engineer Data Architect

EXTERNAL SOURCES

• Wikipedia - Hash function
• NIST - Official hash function definition
• IETF - SHA implementations and definitions
• Cloudflare - Cryptographic hash overview

TOP QUESTIONS

What makes a hash function cryptographically secure?

It should be preimage-resistant, second-preimage-resistant, and collision-resistant. Modern choices include SHA-256 and SHA-3.

Category: Requirements

How is hashing different from encryption?

Hashing is one-way and irreversible; encryption is reversible with a key. They serve different purposes.

Category: Misunderstanding

Why add salt to hashed passwords?

Salts prevent precomputed attacks and make identical passwords produce different hashes, strengthening security.

Category: BestPractice

What are common non-cryptographic hashes?

MurmurHash, xxHash, and CityHash are fast for hash tables and partitioning but not for security.

Category: Technology

What is consistent hashing used for?

It distributes keys across nodes while minimizing remapping during scaling, useful in distributed systems.

Category: Application

Can two inputs share the same hash?

Yes, collisions are possible due to pigeonhole principle, though rare for good functions.

Category: Explanation

How to verify file integrity with hashing?

Compute and compare checksums (e.g., SHA-256). Use authenticated methods for tamper resistance.

Category: BestPractice

Is MD5 still safe?

No. MD5 is vulnerable to collisions and should not be used for security-sensitive purposes.

Category: Risk

Where is hashing used in databases?

Hash indexes, partitioning, deduplication, and change detection rely on hashing for speed and integrity.

Category: Application