Hashing

Hashing is a cryptographic technique that transforms any input — such as a password, file, or message — into a fixed-length string of characters known as a hash value or digest. Unlike encryption, hashing is a one-way function: once data has been hashed, it cannot be reversed back to its original form. This property makes hashing ideal for verifying data integrity and securely storing sensitive information. In cybersecurity, hashing is widely used for password storage, digital signatures, file integrity checks, and blockchain technology. Popular algorithms include SHA-256, SHA-3, and the older but less secure MD5. Hashing ensures that even the smallest change in input produces a completely different output, which is critical for detecting tampering or corruption.

How it works

Hash functions process input data through a mathematical algorithm and output a unique digest of fixed length.

• Deterministic → the same input always produces the same hash.
• Irreversible → it’s computationally infeasible to recover the original input from the hash.
• Collision-resistant → ideally, no two different inputs produce the same hash.
• Avalanche effect → small input changes create drastically different outputs.

Why it matters

Hashing plays a crucial role in protecting data and maintaining trust in digital systems. Passwords are stored as hashes rather than plain text, ensuring attackers cannot easily use them even if a database is leaked. Hashing also verifies the authenticity of downloads, software updates, and blockchain transactions, ensuring no unauthorized alterations have occurred.

Examples

• Websites store password hashes using algorithms like bcrypt or Argon2.
• File integrity is checked by comparing downloaded software’s SHA-256 hash with the one provided by the vendor.
• Blockchain transactions are secured using hashing functions to link blocks together.