SHA-3

As explained in Real-World Cryptography

SHA-3 is a standardized family of cryptographic hash functions based on the Keccak sponge construction.

When a hash must resist collisions, pre-image attacks, and second pre-image attacks—and avoid length-extension attacks—SHA-3 offers a modern standardized choice. It is based on Keccak’s sponge construction rather than the Merkle–Damgård construction used by SHA-2. section 2.5.2 section 2.7

A high-level SHA-3 computation proceeds through these ideas:

• Start with a reversible permutation, keccak-f, which maps a state to another state of the same size. section 2.5.2
• Split the permutation state into a rate and a capacity, then absorb input by XORing blocks into the rate and permuting repeatedly. section 2.5.2
• Squeeze the digest by repeatedly permuting the state and retrieving as much rate as the requested output requires. section 2.5.2

Choosing a SHA-3 variant

SHA-3-256 produces a 256-bit digest; the standardized family also includes SHA-3-224, SHA-3-384, and SHA-3-512. section 2.5.2

Figure 2.6 SHA-2 and SHA-3, the two most widely adopted hash functions. SHA-2 is based on the Merkle–Damgård construction, while SHA-3 is based on the sponge construction.

Use the comparison diagram to distinguish SHA-3’s sponge construction from SHA-2’s Merkle–Damgård construction. section 2.5

How Real-World Cryptography covers it

How deep it goes

Explains permutations, rate, capacity, absorption, and squeezing at a high level while deferring keccak-f internals.

Examples

Uses permutation diagrams, rate-and-capacity diagrams, XOR absorption examples, and SHA-3 output variants.

What it assumes

Assumes basic hash-function security properties while explaining the sponge construction from its permutation components.

What you can do after

Evaluate SHA-3 variants and understand how sponge absorption and squeezing produce a digest.

How it connects

Connects SHA-3 with SHA-2, Keccak, sponge construction, Merkle–Damgård construction, and length-extension attacks.

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Also explained in

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  Software Security for DevelopersSHA-3 is a family of cryptographic hash algorithms standardized with multiple output sizes including 224, 256, 384, and 512 bits.
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Related concepts

• sponge constructionimplements · A sponge construction absorbs input into a state through repeated permutation applications and squeezes output from that state, supporting outputs of arbitrary length.
• hash functionkind of · A hash function deterministically maps input data to a value in a bounded output range, commonly for indexing, lookup, comparison, or integrity checking.
• cryptographic hashkind of · 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.
• cryptographic algorithmkind of · A cryptographic algorithm is a mathematical procedure that transforms data or generates cryptographic values to provide security properties such as confidentiality, integrity, or authentication.

This explainer was generated by Manning's knowledge graph from the text of Real-World Cryptography. The section links point to the parts of the book it draws on.