What is a Cryptographic Hash?

[pwgit-create]

A cryptographic hash is a mathematical function that converts data (like a file, password, or message) into a fixed-size string of characters called a hash value, digest, or checksum.

Example:

hello.txt
↓
SHA-256
↓
2cf24dba5fb0a30e26e83b2ac5b9e29e...

Even a tiny change in the file produces a completely different hash.

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Main properties of a cryptographic hash

1. Deterministic

The same input always produces the same hash.

"hello" → same hash every time

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2. One-way function

You cannot realistically reverse the hash to recover the original data.

This is what makes hashes useful for:

• password storage
• integrity verification
• digital signatures

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3. Avalanche effect

A tiny modification completely changes the output.

Example:

hello
↓
2cf24d...

hello!
↓
ce0609...

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4. Fixed output size

Regardless of input size, the hash length stays the same.

Examples:

• SHA-256 → always 256 bits
• SHA3 → configurable
• BLAKE2b → configurable, often 512 bits

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Why cryptographic hashes matter for file integrity

Your scanner works because:

1. A file is hashed during the initial scan
2. The hash is stored
3. Future scans recompute the hash
4. If the hashes differ, the file changed

This allows detection of:

• tampering
• corruption
• unauthorized modifications
• malware-altered files

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