SHAKE(3)

💖 SHAKE(3) — like, the manual page for the SHAKE functions 💖

okay bestie, sit down, hydrate, and let me tell you about SHAKE — it's a real one from the Message Digest (MD4, MD5, etc.) Support Library (that's libmd, link it with -lmd) ✨

No cap, this is the page for the functions that do NIST FIPS PUB 202: SHA-3 Standard: Permutation-Based Hash and Extendable-Output Functions. Say that five times fast, I dare you 🫶

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🦋 LIBRARY 🦋

Message Digest (MD4, MD5, etc.) Support Library — that's libmd, and you link it with -lmd. periodt 💅

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✨ SYNOPSIS ✨

#include <sha3.h>

void
SHAKE128_Init(SHAKE128_CTX *ctx);

void
SHAKE128_Update(SHAKE128_CTX *ctx, const uint8_t *buf, size_t len);

void
SHAKE128_Final(uint8_t *output[], size_t outlen, SHAKE128_CTX *ctx);

void
SHAKE256_Init(SHAKE256_CTX *ctx);

void
SHAKE256_Update(SHAKE256_CTX *ctx, const uint8_t *buf, size_t len);

void
SHAKE256_Final(uint8_t *output[], size_t outlen, SHAKE256_CTX *ctx);

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🌸 DESCRIPTION 🌸

So the SHAKE functions are the extendable-output functions from the NIST SHA-3 standard, FIPS PUB 202. The whole vibe is: you absorb an arbitrary-length message m, and you get back an arbitrary-length output — either SHAKE128(m) or SHAKE256(m) — truncated to a specified number of octets. Arbitrary in, arbitrary out, that's the whole point, iconic behavior fr fr 🔥

Heads up bestie: before you touch the SHAKE functions, your app should first call SHA3_Selftest(3) and confirm that it succeeded. Do not skip this. It's giving "safety check before the main character moment" 💀

Only the SHAKE128 functions are specified in detail here — the SHAKE256 functions are analogous. (Same energy, different number, iykyk 🌈)

The caller must allocate memory for a SHAKE128_CTX object to hold the state of a SHAKE128 computation over a message. And here's the cute part: SHAKE128_CTX objects may be copied or relocated in memory. Slay, they're portable like that 🎀

🧚 SHAKE128_Init(ctx)

Initialize a SHAKE128 context. This must be done before any other operations on ctx. Like, no exceptions, no shortcuts, do it first 💖

🧚 SHAKE128_Update(ctx, data, len)

Append len octets at data to the message. Just keep feeding it, it's hungry, it can take as much as you've got 🍓

🧚 SHAKE128_Final(output, outlen, ctx)

Store at output the first outlen octets of the SHAKE128 output for the message obtained by concatenating all prior inputs to SHAKE128_Update() on ctx. This is the moment, the finale, the main character walk-off 👑

okay so listen: subsequent use of ctx is not allowed after this, unless it is reinitialized with SHAKE128_Init(). No zombie contexts, we don't do that here 🙈

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👀 SEE ALSO 👀

• sha3(3)
• SHA3_Selftest(3)

go read those too, bestie, it's a whole ecosystem 🦋

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⭐ STANDARDS ⭐

National Institute of Standards and Technology, SHA-3 Standard: Permutation-Based Hash and Extendable-Output Functions, August 2015, FIPS PUB 202. The receipt, the source, the whole lore 📜✨

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💜 AUTHORS 💜

Taylor R Campbell <campbell+sha3@mumble.net> — thank you for your service, king 🫶👑

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and that's the tea! this page came to you from Debian, dated October 14, 2015, and it lives at SHAKE(3) in the manual. mwah, go hash something cute 💅💖🌈