SHA256_INIT(3SSL)

📦
version 4.0.3 · 14 versions
, in ubuntu stonking

🌸 SHA256_INIT(3SSL) — bestie's guide to the Secure Hash Algorithm 💅

okay so this is a page from the OpenSSL manual, section 3SSL, and it's literally the whole SHA family hanging out together. pull up a chair, we're hashing 🫶

✨ NAME ✨

SHA1, SHA1_Init, SHA1_Update, SHA1_Final, SHA224, SHA224_Init, SHA224_Update, SHA224_Final, SHA256, SHA256_Init, SHA256_Update, SHA256_Final, SHA384, SHA384_Init, SHA384_Update, SHA384_Final, SHA512, SHA512_Init, SHA512_Update, SHA512_Final — Secure Hash Algorithm 🎀

✨ SYNOPSIS ✨

first things first, you gotta grab the header, bestie:

#include <openssl/sha.h>

these ones are the current glow-up versions, the one-shot baddies:

unsigned char *SHA1(const unsigned char *data, size_t count, unsigned char *md_buf);
unsigned char *SHA224(const unsigned char *data, size_t count, unsigned char *md_buf);
unsigned char *SHA256(const unsigned char *data, size_t count, unsigned char *md_buf);
unsigned char *SHA384(const unsigned char *data, size_t count, unsigned char *md_buf);
unsigned char *SHA512(const unsigned char *data, size_t count, unsigned char *md_buf);
⚠️ and then… the rest. 💀 the following functions have been deprecated since OpenSSL 3.0, and you can hide them entirely by defining OPENSSL_API_COMPAT with a suitable version value — check openssl_user_macros(7) for the deets.
int SHA1_Init(SHA_CTX *c);
int SHA1_Update(SHA_CTX *c, const void *data, size_t len);
int SHA1_Final(unsigned char *md, SHA_CTX *c);

int SHA224_Init(SHA256_CTX *c);
int SHA224_Update(SHA256_CTX *c, const void *data, size_t len);
int SHA224_Final(unsigned char *md, SHA256_CTX *c);

int SHA256_Init(SHA256_CTX *c);
int SHA256_Update(SHA256_CTX *c, const void *data, size_t len);
int SHA256_Final(unsigned char *md, SHA256_CTX *c);

int SHA384_Init(SHA512_CTX *c);
int SHA384_Update(SHA512_CTX *c, const void *data, size_t len);
int SHA384_Final(unsigned char *md, SHA512_CTX *c);

int SHA512_Init(SHA512_CTX *c);
int SHA512_Update(SHA512_CTX *c, const void *data, size_t len);
int SHA512_Final(unsigned char *md, SHA512_CTX *c);

✨ DESCRIPTION ✨

so listen 🫶 — every single function on this page except SHA1(), SHA224(), SHA256(), SHA384() and SHA512() is deprecated. no cap. apps should be using EVP_DigestInit_ex(3), EVP_DigestUpdate(3) and EVP_DigestFinal_ex(3) instead, or the quick one-shot EVP_Q_digest(3). 👑

the good news? SHA1(), SHA224(), SHA256(), SHA384(), and SHA256() can continue to be used. they can also be replaced by, like, this:

    (EVP_Q_digest(d, n, md, NULL, NULL, "SHA256", NULL) ? md : NULL)

🌈 the actual vibe

SHA-1 (Secure Hash Algorithm) is a cryptographic hash function with a 160 bit output. iconic.

SHA1() computes the SHA-1 message digest of the n bytes at d and places it in md — which must have space for SHA_DIGEST_LENGTH == 20 bytes of output. if md is NULL, the digest goes into a static array.

⚠️ heads up bestie: setting md to NULL is not thread safe. like, at all. 🙈

🦋 for when your message isn't all in memory

the following functions may be used if the message is not completely stored in memory:

  • SHA1_Init() — initializes a SHA_CTX structure. it's giving setup era ✨
  • SHA1_Update() — can be called repeatedly with chunks of the message to be hashed (len bytes at data). feed it little by little, she eats 🍓
  • SHA1_Final() — places the message digest in md, which must have space for SHA_DIGEST_LENGTH == 20 bytes of output, and erases the SHA_CTX. clean exit, we love to see it 💅

🌸 the whole family

the SHA224, SHA256, SHA384 and SHA512 families of functions operate in the same way as for the SHA1 functions. noted 📝

  • SHA224 and SHA256 use a SHA256_CTX object instead of SHA_CTX
  • SHA384 and SHA512 use SHA512_CTX
  • the buffer md must have space for the output from the SHA variant being used — defined by SHA224_DIGEST_LENGTH, SHA256_DIGEST_LENGTH, SHA384_DIGEST_LENGTH and SHA512_DIGEST_LENGTH
⚠️ also, just like with SHA1() above, the SHA224(), SHA256(), SHA384() and SHA512() functions are not thread safe if md is NULL. i'm serious, protect your threads 🫶

✨ RETURN VALUES ✨

SHA1(), SHA224(), SHA256(), SHA384() and SHA512() return a pointer to the hash value. that's your girl right there 🔥

SHA1_Init(), SHA1_Update() and SHA1_Final() and equivalent SHA224, SHA256, SHA384 and SHA512 functions return 1 for success, 0 otherwise. simple as. ⭐

✨ CONFORMING TO ✨

  • US Federal Information Processing Standard FIPS PUB 180-4 (Secure Hash Standard)
  • ANSI X9.30

certified. credentialed. official™ 👑

✨ SEE ALSO ✨

go read those, bestie, iykyk 💜

✨ HISTORY ✨

all of these functions except SHA*() were deprecated in OpenSSL 3.0. the glow-up was real. 💀

Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.

aaaaand that's the whole page, no skips, no summarising, we ate and left no crumbs 🍽️✨

version 4.0.3, dated 2026-09-29, from the SHA256_INIT(3SSL) manual page. mwah 💋 bye bestie, go hash something responsibly 🦋

📦 where this page comes from