PKCS7_DECRYPT(3SSL)

📦
version 4.0.3 · 16 versions
, in ubuntu stonking

💖 PKCS7_DECRYPT 💖

okay so bestie, welcome to PKCS7_decrypt — it lives in the OpenSSL 3SSL manual fam, and its whole entire job is to decrypt content from a PKCS#7 envelopedData structure. that's it. that's the girl. 🎀

✨ SYNOPSIS ✨

#include <openssl/pkcs7.h>

int PKCS7_decrypt(PKCS7 *p7, EVP_PKEY *pkey, X509 *cert, BIO *data, int flags);

🌸 DESCRIPTION 🌸

so PKCS7_decrypt() reaches into a PKCS#7 envelopedData structure, pulls the content out, and decrypts it. main character behaviour only. 👑

here's the cast, and nobody gets cut:

  • p7 — the PKCS#7 structure you're cracking open.
  • pkey — the private key of the recipient. this is the whole lock-and-key moment.
  • cert — the recipient's certificate.
  • data — a BIO that the content gets written to.
  • flags — an optional lil set of flags. optional!! not required!! 💅

🦋 NOTES 🦋

okay so plot twist: even though the recipient's certificate is not needed to actually decrypt the data, it is needed to locate the appropriate recipient inside the PKCS#7 structure — and bestie there can be several of them in there. so like, bring the cert anyway. it's giving utility player. ✨

now this next part is the real tea, so listen up:

when RSA PKCS#1 v1.5 Key Transport is in use, the EVP_PKEY_decrypt() call that gets invoked uses an implicit rejection mechanism. it always returns the result of the RSA decryption of the symmetric key, specifically to avoid the Marvin attack. every time. no exceptions. 🛡️

and the way that result is deterministic?? it can legitimately happen to match the symmetric cipher used for the content encryption. wild but true.

here's the sketchy bit though 🚨: in the case where the certificate is not provided, the last RecipientInfo that produces a key that looks valid will get used. looks valid ≠ is valid, bestie. so heads up — that situation may cause you to get garbage content on decryption. no cap. 😭

the following flags can be passed in the flags parameter:

  • PKCS7_TEXT — when this flag is set, MIME headers for type text/plain get deleted from the content. and if the content is not of type text/plain, then an error is returned. so it's text/plain or it's trouble. 🙈

💫 RETURN VALUES 💫

PKCS7_decrypt() returns either 1 for success or 0 for failure. if you got a 0, the error can be obtained from ERR_get_error(3). go get her. 🔍

💀 BUGS 💀

PKCS7_decrypt() must be passed the correct recipient key and certificate. it does not figure this out for you. it has zero detective energy. 🕵️♀️

it would be better if it could look up the correct key and certificate from a database. it cannot. it simply does not. that's the bug note, periodt. 🫶

🌈 SEE ALSO 🌈

Copyright 2002-2026 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 bestie!! 💖✨ this was OpenSSL version 4.0.3, dated 2026-09-29, out of the OpenSSL project — thank you for coming to my ted talk, go decrypt something, slay, and remember: bring the cert. 🎀🦋💅

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