SHA256_INIT(3ossl)

📦 version 3.5.0, in opensuse-leap 16.0

💅 SHA256_INIT — aka the OpenSSL 3ossl manual, but make it make sense

okay so bestie, gather round, because this page is literally the whole Secure Hash Algorithm family (SHA-1, SHA-224, SHA-256, SHA-384, SHA-512) in one place — it's giving "one manual to rule them all" energy and we are obsessed. It's the 3ossl manual page, and yes, she's iconic. 🎀

✨ 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 — all of these slay together under one name: Secure Hash Algorithm. 🦋

✨ SYNOPSIS ✨

First up, the header you gotta include, no cap:

#include <openssl/sha.h>

Then the one-shot girlies — these are the ones that are still in their main character era:

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);

🫶 the deprecated girlies (since OpenSSL 3.0)

okay so these ones have been deprecated since OpenSSL 3.0, and you can hide them entirely by defining OPENSSL_API_COMPAT with a suitable version value — see 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 ✨

Real talk: all of the functions on this page are deprecated except SHA1(), SHA224(), SHA256(), SHA384() and SHA512(). So if you're writing new code, don't be that girl using the old ones. 🙈

Instead, applications should use EVP_DigestInit_ex(3), EVP_DigestUpdate(3) and EVP_DigestFinal_ex(3) — or the quick one-shot function EVP_Q_digest(3) if you're in a rush (we love a shortcut).

SHA1(), SHA224(), SHA256(), SHA384(), and SHA256() can continue to be used. They can also be replaced by, e.g.,

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

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

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 is placed in a static array.

⚠️ Note: setting md to NULL is not thread safe. Like, at all. Don't do it in a threaded app, bestie, I'm begging. 😭

🧚 the streaming girlies

The following functions may be used if the message is not completely stored in memory — i.e. when you're hashing in chunks and can't just hand over the whole buffer:

  • SHA1_Init() initializes a SHA_CTX structure.
  • SHA1_Update() can be called repeatedly with chunks of the message to be hashed (len bytes at data).
  • 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.

🌈 the whole family

The SHA224, SHA256, SHA384 and SHA512 families of functions operate in the same way as for the SHA1 functions. Little glow-up details tho:

  • Note that 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 note that, as for the SHA1() function above, the SHA224(), SHA256(), SHA384() and SHA512() functions are not thread safe if md is NULL. Same warning, all five of them. 💀

✨ RETURN VALUES ✨

  • SHA1(), SHA224(), SHA256(), SHA384() and SHA512() return a pointer to the hash value. 🎀
  • SHA1_Init(), SHA1_Update() and SHA1_Final() and equivalent SHA224, SHA256, SHA384 and SHA512 functions return 1 for success, 0 otherwise.

✨ CONFORMING TO ✨

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

Certified, standardized, validated. 👑

✨ SEE ALSO ✨

(These are the glow-up versions, go check 'em out, iykyk. 🦋)

✨ HISTORY ✨

All of these functions except SHA*() were deprecated in OpenSSL 3.0. So the SHA*() ones are still eating, everything else got sent to the deprecated bin. 🔥

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>.

🌸 okay that's the whole page, you ate that. this was OpenSSL 3.5.0, dated 2026-09-25 — go forth and hash responsibly, bestie. 💖✨🎀

📦 where this page comes from