SMIME_WRITE_ASN1(3SSL)

📦
version 4.0.3 · 13 versions
, in ubuntu stonking

💌 SMIME_WRITE_ASN1 💌

okay bestie, so this is the SMIME_write_ASN1 page from the OpenSSL manual (section 3SSL, obvi) and it's literally about turning your lil object structure into a whole S/MIME message. it's giving mail-formatting main character energy 🎀

✨ NAME ✨

SMIME_write_ASN1_ex, SMIME_write_ASN1 — convert 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 🌸

so SMIME_write_ASN1_ex() literally, no cap, adds the appropriate MIME headers to an object structure so you get an S/MIME message out the other side. it's the glow-up from "raw structure" to "sendable message" 💅

here's the breakdown, bestie:

  • out is the BIO you're writing the data to.
  • value is the appropriate ASN1_VALUE structure — so either CMS_ContentInfo or PKCS7. if streaming is enabled, then the content has to be supplied via data.
  • flags is an optional set of flags. (optional bestie, but iconic.)
  • ctype_nid is the NID of the content type.
  • econt_nid is the NID of the embedded content type.
  • mdalgs is a list of signed data digestAlgorithms.
  • valid values that the ASN.1 structure it can use are ASN1_ITEM_rptr(PKCS7) or ASN1_ITEM_rptr(CMS_ContentInfo).
  • the library context libctx and the property query propq get used when retrieving algorithms from providers. 🔮

📝 NOTES 📝

real talk: the higher level functions SMIME_write_CMS(3) and SMIME_write_PKCS7(3) should be used instead of SMIME_write_ASN1(). like, just use those, bestie, they're right there 🙈

the following flags can be passed in the flags parameter:

  • 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. (both or it doesn't count, periodt.)
  • 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.
  • 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. don't be out here setting it randomly 😭
  • 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. yeah. twice. iconic but expensive 💀
  • 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. very specific, very demure ✨

🫶 RETURN VALUES 🫶

SMIME_write_ASN1_ex() and SMIME_write_ASN1() return 1 for success or 0 for failure. that's it, that's the vibe check. 1 = slay, 0 = not slay 😭

👀 SEE ALSO 👀

go read those too, bestie, they're the supporting cast 🧚

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>.

and that's the whole page, fr fr 💖 this was SMIME_WRITE_ASN1 from OpenSSL version 4.0.3, dated 2026-09-29 — mwah, stan, go write some S/MIME messages bestie 💅✨

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