MD5(3ossl)

✨ MD5(3ossl) ✨

okay bestie, buckle up, we're doing the OpenSSL hash girlies today 💅 this page covers the whole MD2 / MD4 / MD5 squad — the old-school trio that your codebase probably still calls at 2am and you're like "why are you like this". no judgement, we've all been there 🫶

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🌸 NAME 🌸

MD2, MD4, MD5, MD2_Init, MD2_Update, MD2_Final, MD4_Init, MD4_Update, MD4_Final, MD5_Init, MD5_Update, MD5_Final — the MD2, MD4, and MD5 hash functions ✨

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🎀 SYNOPSIS 🎀

heads up bestie: all of the stuff below is deprecated since OpenSSL 3.0, and you can hide it entirely by defining OPENSSL_API_COMPAT with a suitable version value — check openssl_user_macros(7) for the deets. 💀

the MD2 crew, deprecated since OpenSSL 3.0, hideable with OPENSSL_API_COMPAT + 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);

the MD4 girlies, also deprecated since OpenSSL 3.0, also hideable with OPENSSL_API_COMPAT + a suitable version value (see openssl_user_macros(7) again bestie):

#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 the MD5 main characters, you guessed it, deprecated since OpenSSL 3.0, hideable with OPENSSL_API_COMPAT + 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);

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🦋 DESCRIPTION 🦋

🚨 all of the functions on this page are deprecated 🚨 bestie, applications should be using EVP_DigestInit_ex(3), EVP_DigestUpdate(3) and EVP_DigestFinal_ex(3) instead. that's the move. periodt.

MD2, MD4, and MD5 are cryptographic hash functions with a 128 bit output ✨

MD2(), MD4(), and MD5() compute the MD2, MD4, and MD5 message digest of the n bytes at d and drop it into md — and md must have space for MD2_DIGEST_LENGTH == MD4_DIGEST_LENGTH == MD5_DIGEST_LENGTH == 16 bytes of output, no cap 🧚 if md is NULL, the digest gets placed in a static array instead. iconic behaviour honestly.

the following functions are the ones you reach for when the message isn't completely stored in memory (i.e. you're streaming it, main character energy):

• 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. 🫧

MD4_Init(), MD4_Update(), MD4_Final(), MD5_Init(), MD5_Update(), and MD5_Final() are analogous using an MD4_CTX and MD5_CTX structure. The parameter MUST NOT be NULL. 😭

Applications should use the higher level functions EVP_DigestInit(3) etc. instead of calling the hash functions directly. like, genuinely. 💅

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⭐ 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. ngl bestie, MD5 is giving "my password from 2009". 🔥

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💜 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.

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🌈 CONFORMING TO 🌈

RFC 1319, RFC 1320, RFC 1321 — she's certified, she's documented, she's vintage ✨

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🔥 SEE ALSO 🔥

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

go check these instead, they're the upgraded versions and they ate 💅

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🕰️ HISTORY 🕰️

All of these functions were deprecated in OpenSSL 3.0. that's the whole history section, short and devastating 😭

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📜 COPYRIGHT 📜

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>.

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and that's the whole page bestie, you ate that 🫶 this was OpenSSL 3.5.9, dated 2026-09-29, and yes the manual page is literally called MD5(3ossl) — slay, go hash responsibly (with SHA-3 tho) 💅✨🎀