What is hashing?
Hashing turns any data into a fixed length fingerprint that cannot be reversed, used to check files and store passwords.
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Hashing runs data through a one way function that produces a short, fixed size fingerprint called a hash or digest. Change a single letter in the input and the whole hash changes. It is like a fingerprint of a person: it identifies them, but you cannot rebuild the person from the print. Common algorithms are SHA-256 for files and bcrypt or Argon2 for passwords.
Download pages publish a SHA-256 checksum so you can verify the file was not corrupted or tampered with. Git names every commit by its hash. Websites never store your password, only its hash; at login they hash what you typed and compare. Encryption is different: it can be undone with a key, hashing cannot.
sha256sum ubuntu.iso
echo -n "hello" | sha256sumSee also: What is encryption? and What is a commit?
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See also
- 0354 sudo rules: give a user exactly the rights they need Write sudoers rules with visudo: full admin for operators, a short list of commands for a deploy account, no-password rules for automation,… Intermediate · Step by step · Linux Article Secrets & access · Users, sudo & hardening 15 Oct 2026
- 0357 Keep secrets out of git: .env files, gitignore and what to do after a leak Load passwords and API keys from an untracked .env file, commit a safe .env.example instead, catch mistakes before they are pushed, and… Beginner · Step by step · Any system Article Housekeeping · Secrets & access 15 Oct 2026
Repos in the wild
- Gitleaks: find secrets that were committed to a Git repository gitleaks/gitleaks Gitleaks scans Git history, working trees and arbitrary files for passwords, API keys, tokens and private keys using a library of patterns, and is usually run as a pre-commit hook and in CI. GitHub
- age: a small, modern tool for encrypting files FiloSottile/age age is a simple file encryption tool and Go library with short public keys, SSH key support and no configuration options, designed as a modern replacement for ad hoc GPG use when you need to encrypt a backup or a secret. GitHub
History
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- Dominik +792 chars