MDC2_INIT(3ossl)

✨ MDC2_INIT(3ossl) — okay bestie, let’s talk MDC2 ✨

This is the MDC2_INIT(3ossl) manual page, and it’s giving old-school OpenSSL hash energy. Yes, the whole fam is deprecated, but the facts still matter, so here we go 💅.

🌸 NAME 🌸

MDC2, MDC2_Init, MDC2_Update, MDC2_Final — the MDC2 hash function. That’s the whole name vibe.

🎀 SYNOPSIS 🎀

#include <openssl/mdc2.h>

The following functions have been deprecated since OpenSSL 3.0, and can be hidden entirely by defining OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7):

unsigned char *MDC2(const unsigned char *d, unsigned long n,
                    unsigned char *md);

int MDC2_Init(MDC2_CTX *c);
int MDC2_Update(MDC2_CTX *c, const unsigned char *data,
                unsigned long len);
int MDC2_Final(unsigned char *md, MDC2_CTX *c);

🦋 DESCRIPTION 🦋

Okay so all of the functions described on this page are deprecated. Not me being dramatic — that’s literally the manual. Applications should instead use EVP_DigestInit_ex(3), EVP_DigestUpdate(3), and EVP_DigestFinal_ex(3). Slay for EVP, RIP for direct MDC2 calls 😭.

MDC2 is a method to construct hash functions with 128 bit output from block ciphers. These functions are an implementation of MDC2 with DES. Iconic? Sure. Old? Also yes.

The way that MDC2() works: it computes the MDC2 message digest of the n bytes at d and places it in md (which must have space for MDC2_DIGEST_LENGTH == 16 bytes of output). If md is NULL, the digest is placed in a static array. Lowkey important: that’s the manual’s rule, not a suggestion.

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

• MDC2_Init() — initializes a MDC2_CTX structure.
• MDC2_Update() — can be called repeatedly with chunks of the message to be hashed (len bytes at data).
• MDC2_Final() — places the message digest in md, which must have space for MDC2_DIGEST_LENGTH == 16 bytes of output, and erases the MDC2_CTX.

Applications should use the higher level functions EVP_DigestInit(3) etc. instead of calling the hash functions directly. That’s the whole “please stop using the deprecated thing” vibe 💅.

💖 RETURN VALUES 💖

• MDC2() returns a pointer to the hash value.
• MDC2_Init(), MDC2_Update(), and MDC2_Final() return 1 for success, 0 otherwise.

Like, binary success. Very main character.

🌈 CONFORMING TO 🌈

ISO/IEC 10118-2:2000 Hash-Function 2, with DES as the underlying block cipher. Fr fr, that’s the standard.

👑 SEE ALSO 👑

• EVP_DigestInit(3)

That’s the only SEE ALSO babe — no extra links invented.

⭐ HISTORY ⭐

All of these functions were deprecated in OpenSSL 3.0. Periodt.

🍓 COPYRIGHT 🍓

Copyright 2000-2020 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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mwah 💋 — this page is OpenSSL 3.5.0, dated 2026-09-25, and its manual title is MDC2_INIT(3ossl). Footer handled, bestie 🫶.