SMIME_WRITE_ASN1(3ossl)

📦 version 3.5.0, in opensuse-leap 16.0

✨ NAME ✨

okay bestie, welcome to SMIME_WRITE_ASN1(3ossl) — home of SMIME_write_ASN1_ex and SMIME_write_ASN1, the little S/MIME glow-up crew that converts a structure to S/MIME format. 💌

🌸 SYNOPSIS 🌸

#include <openssl/asn1.h>

int SMIME_write_ASN1_ex(BIO *out, ASN1_VALUE *val, BIO *data, int flags,
                        int ctype_nid, int econt_nid,
                        STACK_OF(X509_ALGOR) *mdalgs, const ASN1_ITEM *it,
                        OSSL_LIB_CTX *libctx, const char *propq);

int SMIME_write_ASN1(BIO *out,
    ASN1_VALUE *val, BIO *data, int flags, int ctype_nid, int econt_nid,
    STACK_OF(X509_ALGOR) *mdalgs, const ASN1_ITEM *it);

💖 DESCRIPTION 💖

SMIME_write_ASN1_ex() is the main-character function here: it adds the appropriate MIME headers to an object structure to produce an S/MIME message. 💅

out is the BIO to write the data to. value is the appropriate ASN1_VALUE structure, which is either CMS_ContentInfo or PKCS7. If streaming is enabled then the content must be supplied via data.

flags is an optional set of flags. ctype_nid is the NID of the content type, econt_nid is the NID of the embedded content type, and mdalgs is a list of signed data digestAlgorithms.

Valid values that can be used by the ASN.1 structure it are ASN1_ITEM_rptr(PKCS7) or ASN1_ITEM_rptr(CMS_ContentInfo).

The library context libctx and the property query propq are used when retrieving algorithms from providers. fancy provider energy ✨

🎀 NOTES 🎀

real talk, bestie: the higher level functions SMIME_write_CMS(3) and SMIME_write_PKCS7(3) should be used instead of SMIME_write_ASN1(). They are the serve-and-protect versions; this one is the lower-level one. 🫶

The following flags can be passed in the flags parameter:

  • CMS_DETACHED — If CMS_DETACHED is set then cleartext signing will be used. This option only makes sense for SignedData where CMS_DETACHED is also set when the sign() method is called.
  • CMS_TEXT — If the CMS_TEXT flag is set, MIME headers for type text/plain are added to the content. This only makes sense if CMS_DETACHED is also set.
  • CMS_STREAM — If the CMS_STREAM flag is set, streaming is performed. This flag should only be set if CMS_STREAM was also set in the previous call to a CMS_ContentInfo or PKCS7 creation function.

If cleartext signing is being used and CMS_STREAM is not set then the data must be read twice: once to compute the signature in the sign() method and once to output the S/MIME message. double-reading era, lowkey iconic but also a little extra 😭

If streaming is performed the content is output in BER format using indefinite length constructed encoding except in the case of signed data with detached content where the content is absent and DER format is used.

🦋 RETURN VALUES 🦋

SMIME_write_ASN1_ex() and SMIME_write_ASN1() return 1 for success or 0 for failure. binary mood, periodt 💀

⭐ SEE ALSO ⭐

Copyright 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.

okay that’s the whole page, bestie — OpenSSL 3.5.0, dated 2026-09-25, for SMIME_WRITE_ASN1(3ossl) signing off. stay slay and stay secure! 💅✨

📦 where this page comes from