PKCS7_DECRYPT(3ossl)

📦 version 3.5.0, in opensuse-leap 16.0

💅 PKCS7_DECRYPT 💅

okay so this is the PKCS7_decrypt(3ossl) page from the OpenSSL fam — like, the whole manual, but make it make sense. bestie, we're cracking open an envelopedData structure and getting the actual content out. let's go 🎀

✨ NAME ✨

PKCS7_decrypt — decrypt content from a PKCS#7 envelopedData structure 🔓💖

🌸 SYNOPSIS 🌸

#include <openssl/pkcs7.h>

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

🦋 DESCRIPTION 🦋

so PKCS7_decrypt() literally extracts and decrypts the content from a PKCS#7 envelopedData structure. iconic behavior tbh.

here's the cast of characters:

  • p7 — the PKCS#7 structure we're working with
  • pkey — the private key of the recipient 🔑
  • cert — the recipient's certificate
  • data — a BIO to write the content to
  • flags — an optional set of flags

💜 NOTES 💜

ngl, here's a vibe check on the cert situation: even though the recipient's certificate is not needed to decrypt the data, it is needed to locate the appropriate recipient in the PKCS#7 structure (and yes, there can be several of them, so it's giving "which one of you is the main character" energy 👑).

now, the spicy part 🌶️ — when RSA PKCS#1 v1.5 Key Transport is in use, the invoked EVP_PKEY_decrypt() will use an implicit rejection mechanism. it always returns the result of RSA decryption of the symmetric key, and that's on purpose — to avoid the Marvin attack. no cap, this result is deterministic and can happen to match the symmetric cipher used for the content encryption. so in the case where the certificate is not provided, the last RecipientInfo producing the key looking valid will be used. and that may cause getting garbage content on decryption 😭💀. you've been warned fr fr.

the following flags can be passed in the flags parameter:

  • PKCS7_TEXT — if this is set, MIME headers for type text/plain are deleted from the content. but if the content is not of type text/plain, then an error is returned 🙈.

⭐ RETURN VALUES ⭐

PKCS7_decrypt() returns either 1 for success or 0 for failure. and the error can be obtained from ERR_get_error(3) 🫶

💀 BUGS 💀

okay, listen — PKCS7_decrypt() must be passed the correct recipient key and certificate. it would be better if it could look up the correct key and certificate from a database, but alas, it cannot. that's just the way it is 💅

also, the lack of single pass processing and the need to hold all data in memory (as mentioned in PKCS7_sign()) also applies to PKCS7_verify() 🧚

🌈 SEE ALSO 🌈

Copyright 2002-2016 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 thing, bestie — this page is from version 3.5.0, dated 2026-09-25, and it's the PKCS7_DECRYPT(3ossl) manual. slay, go decrypt something responsibly 💖✨🦋

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