MD5(3SSL)

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version 4.0.3 · 14 versions
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💅 MD5 — the OpenSSL manual, but make it make sense

okay bestie, so this page lives in the OpenSSL manual (section 3SSL, for the devs keeping score 🫶) and it's all about the MD2, MD4, and MD5 hash functions. Like, the OG cryptographic hash girlies. They've been around forever, they're iconic, and they are also so deprecated. Buckle up. 🎀

✨ NAME ✨

MD2, MD4, MD5, MD2_Init, MD2_Update, MD2_Final, MD4_Init, MD4_Update, MD4_Final, MD5_Init, MD5_Update, MD5_Final — these are the MD2, MD4, and MD5 hash functions. the whole squad. 👑

🌸 SYNOPSIS 🌸

⚠️ heads up bestie: everything below is deprecated since OpenSSL 3.0. You can hide all of it entirely by defining OPENSSL_API_COMPAT with a suitable version value — go peek at openssl_user_macros(7) for the deets.

So like, the MD2 crew first:

⚠️ same warning, because yes, it's repeated for each family: deprecated since OpenSSL 3.0, hideable by defining OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7).
#include <openssl/md2.h>

unsigned char *MD2(const unsigned char *d, unsigned long n, unsigned char *md);

int MD2_Init(MD2_CTX *c);
int MD2_Update(MD2_CTX *c, const unsigned char *data, unsigned long len);
int MD2_Final(unsigned char *md, MD2_CTX *c);

Then MD4, obvs:

⚠️ yep, again: deprecated since OpenSSL 3.0, can be hidden entirely by defining OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7).
#include <openssl/md4.h>

unsigned char *MD4(const unsigned char *d, unsigned long n, unsigned char *md);

int MD4_Init(MD4_CTX *c);
int MD4_Update(MD4_CTX *c, const void *data, unsigned long len);
int MD4_Final(unsigned char *md, MD4_CTX *c);

And finally the main character herself, MD5:

⚠️ one more time for the people in the back: deprecated since OpenSSL 3.0, hideable entirely by defining OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7).
#include <openssl/md5.h>

unsigned char *MD5(const unsigned char *d, unsigned long n, unsigned char *md);

int MD5_Init(MD5_CTX *c);
int MD5_Update(MD5_CTX *c, const void *data, unsigned long len);
int MD5_Final(unsigned char *md, MD5_CTX *c);

🦋 DESCRIPTION 🦋

okay so. every single function on this page is deprecated. no cap. applications should use EVP_DigestInit_ex(3), EVP_DigestUpdate(3) and EVP_DigestFinal_ex(3) instead. that's the move now. 💅

MD2, MD4, and MD5 are cryptographic hash functions with a 128 bit output. little guys. 128 bits of pure vibes.

MD2(), MD4(), and MD5() compute the MD2, MD4, and MD5 message digest of the n bytes at d and place it in md — and md must have space for MD2_DIGEST_LENGTH == MD4_DIGEST_LENGTH == MD5_DIGEST_LENGTH == 16 bytes of output. that math is mathing, they're all 16. If md is NULL, the digest gets placed in a static array instead. 🙈

Now — the following functions may be used if the message is not completely stored in memory. streaming era. ✨

  • MD2_Init() initializes a MD2_CTX structure.
  • MD2_Update() can be called repeatedly with chunks of the message to be hashed (len bytes at data).
  • MD2_Final() places the message digest in md, which must have space for MD2_DIGEST_LENGTH == 16 bytes of output, and erases the MD2_CTX. gone. deleted. blocked. 💀

MD4_Init(), MD4_Update(), MD4_Final(), MD5_Init(), MD5_Update(), and MD5_Final() are analogous using an MD4_CTX and MD5_CTX structure. And the parameter MUST NOT be NULL. like, that's not a suggestion bestie.

Applications should use the higher level functions EVP_DigestInit(3) etc. instead of calling the hash functions directly. 👑

⭐ NOTE ⭐

MD2, MD4, and MD5 are recommended only for compatibility with existing applications. In new applications, hashes from the SHA-2 or SHA-3 family should be preferred. sorry to the MD girlies but that's just facts. 🫶

💖 RETURN VALUES 💖

  • MD2(), MD4(), and MD5() return pointers to the hash value. 🎀
  • MD2_Init(), MD2_Update(), MD2_Final(), MD4_Init(), MD4_Update(), MD4_Final(), MD5_Init(), MD5_Update(), and MD5_Final() return 1 for success, 0 otherwise. that's it. binary. slay.

🌈 CONFORMING TO 🌈

RFC 1319, RFC 1320, RFC 1321 📜

🧚 SEE ALSO 🧚

EVP_DigestInit(3), EVP_MD-SHA2(7), EVP_MD-SHA3(7)

iykyk, go read those instead. 💜

👑 HISTORY 👑

All of these functions were deprecated in OpenSSL 3.0. that's the whole lore. 😭

Copyright 2000-2024 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>.

and that's the whole page bestie!! 🎀 this was OpenSSL 4.0.3, dated 2026-09-29, from the MD5(3SSL) page. go forth, use EVP_Digest*, and stay hydrated. 💖✨

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