LIBKECCAK_SHAKESUM_FD(3)

💅 LIBKECCAK_SHAKESUM_FD(3) — like, the SHAKE hashsum of a file, bestie ✨

okay so you found the libkeccak_shakesum_fd page in the Library Functions Manual and you're like "what is this" — don't worry, I got you 🫶 this one function will take a whole file and turn it into a SHAKE hashsum, and yes it's as iconic as it sounds.

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✨ NAME ✨

libkeccak_shakesum_fd — calculate a SHAKE hashsum of a file 🌸

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🎀 SYNOPSIS 🎀

#include <libkeccak.h>

int libkeccak_shakesum_fd(int fd, struct libkeccak_state *state, long int semicapacity, long int output, void *hashsum);

and like, link with -lkeccak obviously 💅

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🦋 DESCRIPTION 🦋

So libkeccak_shakesum_fd() computes a SHAKE hashsum of a file — and the file is specified by its file descriptor fd, which lowkey should be at the beginning of the file, just saying 👀

The hash algorithm gets tuned by two params, semicapacity and output: they're the half of the capacity and the output size, respectively, both in bits. That's it, that's the vibe check 💜

The hash lands in hashsum, in binary form, no hex prettiness here. And hashsum needs an allocation size of at least (((output + 7) / 8) * sizeof(char)) — no cap, size it right 🙈

bestie listen — *state should not be initialised. libkeccak_shakesum_fd() initialises *state itself. So if *state is already initialised, you get a memory leak. not cute. 💀

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🧚 RETURN VALUES 🧚

• Returns 0 when everything slays ✨
• On error, returns -1 and sets errno to describe the error 🔥

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🌈 ERRORS 🌈

libkeccak_shakesum_fd() may fail for any reason — except those that result in errno being set to EINTR, which are specified for the functions read(2), malloc(3), and realloc(3). So yeah, it can fail, just not that way 💅

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👑 NOTES 👑 (read these fr fr)

• Be aware: libkeccak_shakesum_fd() hashes the file until the end has been reached 🌀 For pipes and sockets, that means until the file has been closed. But for character devices? That usually means never. So attempting to hash files in /dev is usually a bad idea — like, genuinely, don't 😭
• libkeccak_shakesum_fd() does not check for the file length or file type before hashing, because that could limit what you can do and would make the library more complex. main character energy: it trusts you ✨
• libkeccak_shakesum_fd() does not stop if interrupted (read(2) returns EINTR). it's committed to the bit 💀
• libkeccak_shakesum_fd() assumes all information is non-sensitive, and will therefore not perform any secure erasure of information. so don't put your secrets in there 🫶
• libkeccak_shakesum_fd() does not validate the tuning of the algorithm. you're on your own for that one 🙈

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🍓 EXAMPLE 🍓

This example calculates the SHAKE256(, 512) hash of the input from stdin, and prints the hash, in hexadecimal form, to stdout. iconic behaviour honestly 👑

struct libkeccak_state state;
if (libkeccak_shakesum_fd(STDIN_FILENO, &state, 256, 512, binhash) < 0)
     goto fail;
libkeccak_behex_lower(hexhash, binhash, sizeof(binhash));
printf("%s\n", hexhash);
libkeccak_state_destroy(&state);

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⭐ SEE ALSO ⭐

libkeccak_behex_lower(3), libkeccak_behex_upper(3), libkeccak_generalised_sum_fd(3), libkeccak_keccaksum_fd(3), libkeccak_sha3sum_fd(3), libkeccak_rawshakesum_fd(3), libkeccak_spec_shake(3), libkeccak_spec_check(3), libkeccak_generalised_spec_initialise(3), libkeccak_state_initialise(3)

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and that's the whole page bestie 💖 this one comes from the LIBKECCAK library, and it's literally pages 3 of the Library Functions Manual — the same LIBKECCAK_SHAKESUM_FD(3) you started with, wrapped up with a bow 🎀 go forth and hash, ily, bye! 💅✨