C implementation of SHA-3 and Keccak with Init/Update/Finalize API
The purpose of this project is:
- provide an API that hashes bytes, not bits
- provide a simple reference implementation of a SHA-3 message digest algorithm, as defined in the FIPS 202 standard
- assist developers in the Etherium blockchain ecosystem by providing the Keccak function used there
- implement the hashing API that employs the IUF paradigm (or
- answer the design questions, such as:
- what does the state for IUF look like?
- how small can the state be (224 bytes on a 64-bit system for a unified SHA-3 algorithm)
- what is the incremental cost of adding e.g. SHA3-384 to a SHA3-256 implementation?
The implementation is written in C and uses
uint64_t types to manage the SHA-3 state. The code will compile and run on 64-bit and 32-bit architectures (
gcc -m32 on
x86_64 were tested).
License, prior work
This work is licensed with a standard MIT license. I appreciate, but do not require, any attribution to this work if you used the code or ideas. I thank you for this in advance.
This is a clean-room implementation of IUF API for SHA3. The
keccakf() is based on the code from keccak.noekeon.org.
1600-bit message hashing test vectors are NIST test vectors.
Overview of the API
Let's hash 'abc' with SHA3-256 using two methods: single buffer (but using IUF paradigm), and using the IUF API.
sha3_context c; uint8_t *hash;
sha3_Init256(&c); sha3_Update(&c, "abc", 3); hash = sha3_Finalize(&c); // 'hash' points to a buffer inside 'c' // with the value of SHA3-256
Alternatively, IUF hashing:
sha3_Init256(&c); sha3_Update(&c, "a", 1); sha3_Update(&c, "bc", 2); hash = sha3_Finalize(&c); // no free for 'c' is needed
hash points to the same
256/8=32 bytes in both cases.
There is also a single-call hashing API:
sha3_HashBuffer(256, SHA3_FLAGS_KECCAK, "abc", 3, out, sizeof(out)); // out contains 256 bits of Keccak256, or less if sizeof(out)<32
How to use Keccak version
sha3_SetFlags(&c, SHA3_FLAGS_KECCAK) immediately after
sha3_InitX or no later than
sha3_Finalize. This change cannot be undone for the given hash context.
Makefile for details. See also below for specific examples.
$ make test Keccak-256 tests passed OK SHA3-256, SHA3-384, SHA3-512 tests passed OK
$ make CFLAGS=-m32 LDFLAGS=-m32 test Keccak-256 tests passed OK SHA3-256, SHA3-384, SHA3-512 tests passed OK
There is also
sha3sum test program that takes following parameters:
sha3sum 256|384|512 file_path
or for Keccak version:
sha3sum 256|384|512 -k file_path
SHA-3 / Linux sha3sum example
$ touch empty.txt $ gcc -Wall sha3.c sha3sum.c -o sha3sum && ./sha3sum 256 empty.txt a7ffc6f8bf1ed76651c14756a061d662f580ff4de43b49fa82d80a4b80f8434a empty.txt
Compare with Linux
$ sha3sum -a 256 empty.txt a7ffc6f8bf1ed76651c14756a061d662f580ff4de43b49fa82d80a4b80f8434a empty.txt
Keccak256 / Solidity example
$ echo -n "abc" > abc $ sha3sum 256 -k abc 4e03657aea45a94fc7d47ba826c8d667c0d1e6e33a64a036ec44f58fa12d6c45 abc
console.log(web3.utils.sha3('abc')); // prints 0x4e03657aea45a94fc7d47ba826c8d667c0d1e6e33a64a036ec44f58fa12d6c45
- the same
sha3_contextobject maintains the state for SHA3-256, SHA3-384, or SHA3-512 algorithm;
- the hash algorithm used is determined by how the context was initialized with
sha3_Finalizeare the same for regardless the type of the algorithm (
- the buffer returned by
Xbits of hash;
sha3_InitXalso works as Reset (zeroization) of the hash context; no Free function is needed;
sha3.h for the exact interface.
Thanks to @ralight for moving the test code into separate
SHA3-224 is not supported, but can easily be added.
The code was written to work with the Microsoft Visual Studio compiler (under
_MSC_VER), but this build target was not tested.
This project was created to support SHA3 in OpenPGP work, but it applies to other protocols and formats, e.g. TLS.