SMIME_READ_CMS(3ossl)

📦 version 3.5.0, in opensuse-leap 16.0

💌 SMIME_READ_CMS(3ossl) — like, the whole vibe

okay so bestie, welcome to the 3ossl corner of the OpenSSL man-verse 🎀 this one's all about SMIME_read_CMS_ex and SMIME_read_CMS, which is literally "parse S/MIME message" energy. yes. that's the name section. we ate. 💅

✨ SYNOPSIS ✨

#include <openssl/cms.h>

CMS_ContentInfo *SMIME_read_CMS_ex(BIO *bio, int flags, BIO **bcont,
                                   CMS_ContentInfo **cms);
CMS_ContentInfo *SMIME_read_CMS(BIO *in, BIO **bcont);

no cap, that's the whole signature situation 🫶

💖 DESCRIPTION 💖

So SMIME_read_CMS() parses a message in S/MIME format. iconic behaviour honestly.

in is a BIO to read the message from. that's your source, your main character, your input stream ✨

If cleartext signing is used then the content is saved in a memory bio which is written to *bcont — otherwise *bcont is set to NULL. lowkey important detail, remember it 🌸

The parsed CMS_ContentInfo structure is returned, or NULL if an error occurred 😭 (sad but honest).

Now for SMIME_read_CMS_ex() — she's similar to SMIME_read_CMS() but optionally a previously created cms CMS_ContentInfo object can be supplied as well as some flags. To create a cms object use CMS_ContentInfo_new_ex(3). iykyk 👑

  • If the flags argument contains CMS_BINARY then the input is assumed to be in binary format and is not translated to canonical form. 🧚
  • If in addition SMIME_ASCIICRLF is set then the binary input is assumed to be followed by CR and LF characters, else only by an LF character. 💅

And if flags is 0 and cms is NULL then it is identical to SMIME_read_CMS(). literally the same function, just wearing a different outfit 💀

📝 NOTES 📝

If *bcont is not NULL then the message is clear text signed. *bcont can then be passed to CMS_verify() with the CMS_DETACHED flag set. periodt. 🔥

Otherwise the type of the returned structure can be determined using CMS_get0_type(). 🦋

To support future functionality, if bcont is not NULL, *bcont should be initialized to NULL. bestie please do this, it's giving future-proofing 💖

For example:

BIO *cont = NULL;
CMS_ContentInfo *cms;

cms = SMIME_read_CMS(in, &cont);

that's it, that's the whole setup 🌈

💀 BUGS 💀

okay so we gotta be honest, the MIME parser used by SMIME_read_CMS() is somewhat primitive. While it will handle most S/MIME messages, more complex compound formats may not work. it's trying its best 🙈

The parser assumes that the CMS_ContentInfo structure is always base64 encoded, and will not handle the case where it is in binary format or uses quoted printable format. no cap, that's a real limitation ⚠️

The use of a memory BIO to hold the signed content limits the size of message which can be processed due to memory restraints: a streaming single pass option should be available. (future feature energy, we're manifesting it ✨)

🎀 RETURN VALUES 🎀

SMIME_read_CMS_ex() and SMIME_read_CMS() return a valid CMS_ContentInfo structure or NULL if an error occurred. The error can be obtained from ERR_get_error(3). so if it flops, that's where the receipts are 🧾

👀 SEE ALSO 👀

the whole crew, fr fr 💜

🌸 HISTORY 🌸

The function SMIME_read_CMS_ex() was added in OpenSSL 3.0. new-ish but already iconic ⭐

Copyright 2008-2021 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>. (yes, read the license bestie, it's not optional 💅)

and that's the page!! mwah 💋 this whole thing shipped with OpenSSL 3.5.0 and the date on it is 2026-09-25 — SMIME_read_CMS(3ossl), signing off 🫶✨ 🍓

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