The purpose of this project is:
- provide an API that hashes bytes, not bits
- provide a simple single-file reference implementation of a SHA-3 message digest algorithm, as defined in the FIPS 202 standard;
- implement the hashing API that employs the IUF paradigm (or
Init
,Update
,Finalize
style). - 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 state. The code will compile and run on 64-bit and 32-bit architectures (gcc
and gcc -m32
on x86_64
were tested).
This work is in public domain.
I would appreciate 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.
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;
Single-buffer hashing:
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
The hash
points to the same 256/8=32
bytes in both cases.
$ gcc -Wall sha3.c -o _ && ./_
SHA3-256, SHA3-384, SHA3-512 tests passed OK
or
$ gcc -m32 Wall sha3.c -o _ && ./_
SHA3-256, SHA3-384, SHA3-512 tests passed OK
- the same
sha3_context
object 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_InitX
, e.g.sha3_Init256
,sha3_Init384
, orsha3_Init512
call; sha3_Update
andsha3_Finalize
are the same for regardless the type of the algorithm (X
);- the buffer returned by
sha3_Finalize
will haveX
bits of hash; sha3_InitX
works also as Reset or Free (zeroization) of the hash context.
See sha3.c
for details.
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.