Cryptographic hash
A cryptographic hash is a fixed-length digest computed from input data by a deterministic function designed to resist preimage, second-preimage, and collision attacks.
Software Security for Developers
A cryptographic hash function maps input data to a fixed-size digest designed to detect changes while resisting reversal and collision generation.
- How it is used
- Uses fixed-size digests to detect accidental changes in files and support security technologies such as HMAC, TLS, JWT, JWE, and JWS.
- How deep it goes
- Explains determinism, fixed-size output, one-wayness, collision resistance, verification steps, limitations, algorithm choice, and Java APIs.
- Examples
- Uses ACME refunds.json validation, SHA-256 file digests, Maven Central artifacts, Git commits, and Java SHA-3 examples.
- What you can do after
- Apply it via Java MessageDigest to detect file corruption and select safer standardized algorithms without confusing integrity with authenticity.
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Real-World Cryptography
A hash function designed to provide security properties such as collision resistance, pre-image resistance, and second pre-image resistance.
- How it is used
- Uses digests to verify downloaded content, external scripts, peer-to-peer chunks, and public-key identities.
- How deep it goes
- Explains security properties, limitations, applications, and SHA-2 and SHA-3 constructions, but defers secret hashing and password hashing.
- Examples
- Shows OpenSSL file and message commands, subresource integrity, BitTorrent chunks, Tor onion addresses, and hexadecimal digests.
- What you can do after
- Apply it via OpenSSL to verify downloaded files and recognize when a digest alone cannot authenticate an untrusted source.
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The Well-Grounded Python Developer: How the pros use Python and Flask
A cryptographic hash is a one-way transformation that maps data to a fixed-format digest designed to make recovery of the original data computationally difficult.
- How it is used
- Protects stored login credentials while allowing submitted passwords to be checked during authentication.
- How deep it goes
- Explains model-level hashing and verification, but does not describe the hash algorithm or its internals.
- Examples
- Uses a `User` model with a write-only password property, a `hashed_password` attribute, and login-form verification.
- What you can do after
- Apply it via Flask-Bcrypt to store password hashes and check submitted passwords in a user model.
Build Python Web Apps with Streamlit
A cryptographic hash function transforms input into a fixed-looking digest such that recovering the original input is computationally difficult.
- How it is used
- Protects user passwords when building signup, login, and database-backed authentication features.
- How deep it goes
- Explains one-way behavior and demonstrates bcrypt storage and verification, without descending into hashing algorithms’ mathematics.
- Examples
- Uses a password-to-digest comparison, a bcrypt User model, and a database row containing a password_hash.
- What you can do after
- Apply bcrypt to store password hashes and verify entered passwords in a Python authentication service.
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Related concepts
- hash functionproduced by · A hash function deterministically maps input data to a value in a bounded output range, commonly for indexing, lookup, comparison, or integrity checking.
- secure hash algorithmincludes · The Secure Hash Algorithm is a family of standardized cryptographic hash functions that map input data to fixed-size digests.
- hash valueproduces · A hash value is a deterministic, typically fixed-size value produced by applying a hash function to input data, often for lookup, comparison, identification, or integrity checking.
- hexadecimal numberuses · A hexadecimal number is a numeral represented in the base-sixteen positional system using symbols 0–9 and A–F for values zero through fifteen.
- data corruptionaddresses · Data corruption is the unintended alteration, loss, or damage of data that makes it inaccurate, invalid, inconsistent, or unusable.
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