Hash function
A hash function deterministically maps input data to a value in a bounded output range, commonly for indexing, lookup, comparison, or integrity checking.
Real-World Cryptography
A hash function maps input data to a fixed-size output and may provide cryptographic properties such as one-wayness and collision resistance.
- How it is used
- Uses fixed-size digests to check integrity, support authenticity, and build cryptographic protocols.
- How deep it goes
- Explains the mapping, three security properties, limitations, applications, algorithm choices, and serialization hazards without implementation-level internals.
- Examples
- Demonstrates file checks, OpenSSL commands, BitTorrent chunks, Tor addresses, commitments, and tampered cryptocurrency transactions.
- What you can do after
- Apply hashing via OpenSSL, compare trusted digests, distinguish cryptographic hashes from checksums, and avoid predictable or ambiguous inputs.
Hacking Cryptography
A function that maps input data to a fixed-size digest, typically designed so that recovering or finding inputs with specified relationships is computationally infeasible.
- How it is used
- Supports password comparison, file-integrity checking, and fixed-size data fingerprints.
- How deep it goes
- Defines resistance properties and constructions, then traces rainbow-table and length-extension failure modes.
- Examples
- Uses password login, DVD checksums, colliding PDFs, rainbow tables, and forged bank API requests.
- What you can do after
- Evaluate/understand where hashes provide comparison or integrity and where password protection or authentication needs stronger constructions.
Grokking Algorithms, Second Edition
A hash function is a deterministic function that maps a key to a value used to determine its storage location in a hash table.
- How it is used
- Turns keys into array locations so a hash table can retrieve stored values without searching through the array.
- How deep it goes
- Works through consistent indexing and collisions with linked-list handling, but stops short of implementing a hash function.
- Examples
- Uses produce-price lookups and exercises comparing how candidate functions distribute phonebook names, battery sizes, and book titles.
- What you can do after
- Evaluate/understand it by checking consistency and distribution and relating collisions to hash-table lookup performance.
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Grokking Data Structures
A hash function is a function that maps input data to a bounded hash value used to compute or organize lookup keys.
- How it is used
- Maps keys to valid array indexes so a hash table can use less space than a direct-access table.
- How deep it goes
- Defines valid outputs and distribution goals, then works through the multiplication method and its use in a chaining implementation.
- Examples
- Uses a baseball-card collection and Python code that extracts object keys and computes bucket indexes.
- What you can do after
- Build it from scratch: compute a bucket index and use it in a hash table with chaining.
Spring Security in Action, Second Edition
A hashing algorithm deterministically transforms input data into an output from which the original input is intended to be impractical to recover.
- How it is used
- Applies hashing to stored data, particularly passwords, within explicitly configured Spring Security authentication and data-protection components.
- How deep it goes
- Explains the security role and configuration boundary but stops short of comparing individual hashing algorithms or implementation internals.
- Examples
- Uses password handling and protected data storage as the principal application examples.
- What you can do after
- Apply it via Spring Security's PasswordEncoder and configure hashing where the application stores protected data.
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Troubleshooting Java, Second Edition
Hashing is the transformation of data into a fixed-size digest that can be compared to detect content differences without transmitting the original data.
- How it is used
- Compares large datasets efficiently during reconciliation and data-integrity checks.
- How deep it goes
- Explains digests, batch and hierarchical comparison, stateless reconciliation, and collision risk, then defers exact mismatch analysis.
- Examples
- Uses SHA-256, daily invoice entries, partitions, batches, replicas, caches, and integration points.
- What you can do after
- Diagnose mismatches efficiently and decide when to perform deeper record-level comparisons.
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Grokking Relational Database Design
A hash function is a function that maps variable-length input data to a fixed-length output value.
- How it is used
- Protects stored passwords by replacing reusable plain text with one-way hash values.
- How deep it goes
- Defines hashing, explains salts and attack methods, and demonstrates storage and login verification.
- Examples
- Uses bcrypt output, Base64 encoding, CHAR(60), and a password comparison during login.
- What you can do after
- Apply bcrypt password hashing, size the database column, and verify login credentials by comparing hashes.
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The Joy of JavaScript
The process of computing a fixed-size digest or hash value from input data using a hash function.
- How it is used
- Uses hashing for transaction identifiers, lookup, integrity checks, and cryptographic links between blockchain blocks.
- How deep it goes
- Explains input assembly, character-based computation, collisions, functional decomposition, purity, and replacement with a more secure algorithm.
- Examples
- Demonstrates transaction objects, a money transaction, chained blockchain blocks, and JavaScript calculateHash implementations.
- What you can do after
- Builds a basic JavaScript hash method, refactors it into composable functions, and swaps in a more secure Node.js crypto algorithm.
First-Party Data Activation
The transformation of input data into a fixed-length value designed for integrity checking, lookup, or comparison without retaining the original representation.
- How it is used
- Enables matching of customer identifiers across partner datasets in a data clean room without exposing raw identifiers during matching.
- How deep it goes
- Defines the transformation and traces a high-level matching workflow, stopping short of hash-algorithm internals.
- Examples
- Uses hashed email addresses and loyalty IDs, plus Google Ads Data Hub’s partner-side and platform-side SHA-256 options.
- What you can do after
- Evaluate/understand it as a matching safeguard while assessing platform trust and controls before sharing customer data.
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Effective Data Analysis
A hash algorithm is a computational procedure that deterministically maps data to a fixed-size hash code.
- How it is used
- Uses deterministic codes to join records while keeping sensitive identifiers out of analytical tables.
- How deep it goes
- Explains deterministic behavior, fixed-size output, practical hashing, and security caveats without detailing algorithm internals.
- Examples
- Demonstrates SHA-256 email hashing in pandas and compares anonymized and pseudonymized records across domains.
- What you can do after
- Apply it via Python hashlib and pandas to create pseudonymous identifiers and separate original values from analysis tables.
Grokking Web Application Security
A hashing algorithm deterministically maps input data to a fixed-size hash value while being designed to make different inputs produce different values with high probability.
- How it is used
- Uses hashes to detect changed data and verify credentials without storing original inputs.
- How deep it goes
- Explains deterministic, one-way behavior, collisions, brute force, and hash comparison through security scenarios.
- Examples
- Uses CDN script verification and Ruby bcrypt password hashing with a salt and comparison.
- What you can do after
- Apply it via Subresource Integrity and bcrypt to detect tampering and verify passwords without storing plain text.
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Python How-To
Hashing is the computation of a compact hash value from input data using a hash function.
- How it is used
- Explains how dictionaries and sets index hashable keys and items, while motivating efficient membership lookup.
- How deep it goes
- Defines hash computation, consistency, collisions, one-way behavior, and hashability, but does not detail collision-resolution algorithms.
- Examples
- Uses Python hash calls, password comparison, dictionary keys, set items, and list-versus-set membership timing.
- What you can do after
- Apply it via Python's hash function to inspect hash values and reason about dictionary keys and set items.
ASP.NET Core in Action, 3e
A hash is a deterministic compact value computed from data such that modifying the data normally changes the resulting value.
- How it is used
- Uses deterministic content values to refresh browser caches and store passwords without retaining plaintext.
- How deep it goes
- Explains content-based cache busting and password-storage guidance, but stops short of hash algorithm internals.
- Examples
- Demonstrates asp-append-version on a script and contrasts unchanged versus modified file query strings.
- What you can do after
- Apply it via ASP.NET Core Tag Helpers for automatic asset versioning and choose expensive password-hashing algorithms for stored credentials.
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Akka in Action, Second Edition
A hashing algorithm is an algorithm that deterministically maps input data to hash values.
- How it is used
- Routes related messages consistently across Akka routees in a group router.
- How deep it goes
- Explains key extraction, hashing, virtual-node selection, and routee selection, while leaving Akka internals invisible to normal users.
- Examples
- Uses command IDs, an Aggregator protocol, and Akka Scala configuration with ServiceKey and a group router.
- What you can do after
- Apply Akka consistent-hashing routing by defining a stable message-key mapping and configuring virtual-node capacity.
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Acing the CCNA Exam: Volume 2 Advanced Networking and Security
A hashing algorithm transforms input data into a fixed-size digest that can support password protection and integrity verification.
- How it is used
- Protects Cisco IOS passwords at rest and supports authentication without storing the original password.
- How deep it goes
- Defines one-way fixed-length conversion and contrasts password storage options, but does not explain algorithm internals.
- Examples
- Uses Cisco IOS enable-secret configuration and running-configuration verification with scrypt output.
- What you can do after
- Configure and verify a Cisco IOS enable secret stored with a selected hashing algorithm.
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Python Workout, Second Edition
A hash function is a function that maps a hashable Python object to an integer hash value used by hash-based data structures.
- How it is used
- Uses hashing to restrict dictionary keys to hashable objects and make key lookup fast.
- How deep it goes
- Explains hash-based lookup through an office analogy and contrasts it with linear sequence search, without detailing collision handling.
- Examples
- Uses numbered offices and surname initials to illustrate direct lookup compared with checking offices sequentially.
- What you can do after
- Evaluate why dictionaries require hashable keys and why their lookups can outperform searches through strings, lists, or tuples.
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Related concepts
- 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.
- SHA-256includes · SHA-256 is a standardized cryptographic hash function in the SHA-2 family that maps arbitrary input data to a fixed-length 256-bit digest.
- cryptographic hashproduces · 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.
- bloom filterused by · A Bloom filter is a space-efficient probabilistic data structure for testing set membership that permits false positives but not false negatives.
- SHA-2includes · SHA-2 is a standardized family of cryptographic hash algorithms that produces fixed-length digests, including SHA-224, SHA-256, SHA-384, and SHA-512.
- HMACused by · HMAC is a keyed message authentication code constructed from a cryptographic hash function and a secret key to authenticate data and verify its integrity.
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