SHA256_INIT(3ossl)

📦
version 15.1 · 2 versions
, in freebsd 15.1

💖 SHA256_INIT(3ossl) — Secure Hash Algorithm 💖

okay bestie, so this is the 3ossl page for the SHA family — SHA1, SHA224, SHA256, SHA384, SHA512 and all their little Init/Update/Final babies. it's giving "old faithful crypto" and honestly? iconic. let's get into it 🎀

✨ 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 🌸

#include <openssl/sha.h>

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);

okay so heads up 🫶 — 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, see openssl_user_macros(7):

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 like, every single function on this page except for SHA1(), SHA224(), SHA256(), SHA384() and SHA512() is deprecated 😭. apps should be using EVP_DigestInit_ex(3), EVP_DigestUpdate(3) and EVP_DigestFinal_ex(3) instead, or the quick one-shot function EVP_Q_digest(3). but plot twist — 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 ✨.

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 — no cap, that's a real one.

🦋 the streaming girlies 🦋

the following functions may be used if the message is not completely stored in memory (iykyk, chunked hashing):

  • 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. quick notes tho:

  • 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 💀

⭐ 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 🌸

🔥 SEE ALSO 🔥

EVP_Q_digest(3), EVP_DigestInit(3) — go read these bestie, fr fr 📚

💜 HISTORY 💜

all of these functions except SHA*() were deprecated in OpenSSL 3.0 ⏳

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>.

ok that's the whole page, no skipped parts, we ate and left no crumbs 💅

and that's a wrap bestie! this one's 3.5.6, dated 2026-04-07 — go hash something and slay 🦋✨💖

📦 where this page comes from