Rate

As explained in Real-World Cryptography

The rate is the portion of a sponge state through which input is absorbed and output is extracted.

In a sponge construction, the rate is the selected portion of a permutation’s state that absorbs input and later supplies output. The remaining portion is the capacity. section 2.5.2

A sponge uses the rate in two phases:

• Absorption: XOR input blocks with the rate, then apply the permutation; repeat when input exceeds the rate size. section 2.5.2
• Extraction: repeatedly apply the permutation and retrieve successive rate portions until enough digest output is available. section 2.5.2

A five-bit rate

With a five-bit rate initialized to zero, absorbing input 00101 XORs those five bits into the rate before the permutation randomizes the state. section 2.5.2

Figure 2.13 The permutation f randomizes an input of size 8 bits into an output of the same size. In a sponge construction, this permutation’s input and output are divided into two parts: the rate (of size r and the capacity (of size c).

A state diagram shows how the permutation’s equal-sized input and output are divided into rate and capacity. section 2.5.2

How Real-World Cryptography covers it

How deep it goes

Defines the state split and works through XOR absorption and repeated extraction, without explaining permutation design.

Examples

Uses an eight-bit state, a five-bit input block, XOR absorption, and iterative rate extraction.

What it assumes

Assumes familiarity with input and output bits, XOR, and permutations while introducing sponge state division.

What you can do after

Evaluate/understand how sponge constructions absorb messages and produce digests through the rate.

How it connects

Connects sponge construction, permutation, capacity, Keccak-f, and SHA-3.

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Related concepts

• sponge constructionpart of · A sponge construction absorbs input into a state through repeated permutation applications and squeezes output from that state, supporting outputs of arbitrary length.

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.