PKCS7_ENCRYPT(3SSL)

💖 PKCS7_ENCRYPT 💖

okay bestie, pull up a chair, because today we're talking about PKCS7_encrypt_ex and PKCS7_encrypt from the pkcs7_encrypt(3ssl) manual page, and honestly? it's giving ✨envelope era✨. no gatekeeping, let's go 🫶

🌸 NAME 🌸

PKCS7_encrypt_ex, PKCS7_encrypt — create a PKCS#7 envelopedData structure 💌

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✨ SYNOPSIS ✨

#include <openssl/pkcs7.h>

PKCS7 *PKCS7_encrypt_ex(const STACK_OF(X509) *certs, BIO *in,
                        const EVP_CIPHER *cipher, int flags,
                        OSSL_LIB_CTX *libctx, const char *propq);
PKCS7 *PKCS7_encrypt(const STACK_OF(X509) *certs, BIO *in,
                     const EVP_CIPHER *cipher, int flags);

literally just look at those signatures, so clean, so demure 💅

🦋 DESCRIPTION 🦋

PKCS7_encrypt_ex() creates and returns a PKCS#7 envelopedData structure. periodt.

let me break down the cast of characters for you (the arguments):

• certs is the list of recipient certificates 🎀
• in is the content to be encrypted 📥
• cipher is the symmetric cipher to use 🔐
• flags is an optional set of flags 🚩
• the library context libctx and the property query propq are used when retrieving algorithms from providers — iykyk 🌐

no cap, important: only RSA keys are supported in PKCS#7 and envelopedData, so the recipient certificates you hand to this function must all contain RSA public keys. they do not have to be signed using the RSA algorithm tho 💜

EVP_des_ede3_cbc() (triple DES) is the algorithm of choice for S/MIME use because most clients will support it. the way that's the safe pick 👑

some old "export grade" clients may only support weak encryption using 40 or 64 bit RC2 😭 these can be used by passing EVP_rc2_40_cbc() and EVP_rc2_64_cbc() respectively.

the algorithm you pass in the cipher parameter must support ASN1 encoding of its parameters. that's not a vibe check you can skip bestie.

many browsers implement a "sign and encrypt" option which is simply an S/MIME envelopedData containing an S/MIME signed message. this can be readily produced by storing the S/MIME signed message in a memory BIO and passing it to PKCS7_encrypt(). iconic honestly 🌈

🎀 the flags 🎀

the following flags can be passed in the flags parameter:

• if the PKCS7_TEXT flag is set, MIME headers for type text/plain are prepended to the data 📝
• normally the supplied content is translated into MIME canonical format (as required by the S/MIME specifications). if PKCS7_BINARY is set, no translation occurs. this option should be used if the supplied data is in binary format otherwise the translation will corrupt it 💀 if PKCS7_BINARY is set then PKCS7_TEXT is ignored. (not the two of them beefing 😭)
• if the PKCS7_STREAM flag is set, a partial PKCS7 structure is output suitable for streaming I/O: no data is read from the BIO in 🌊

⚠️ real talk: if the flag PKCS7_STREAM is set, the returned PKCS7 structure is not complete, and outputting its contents via a function that does not properly finalize the PKCS7 structure will give unpredictable results. unpredictable. results. not cute. 🚨

several functions including SMIME_write_PKCS7(), i2d_PKCS7_bio_stream(), PEM_write_bio_PKCS7_stream() finalize the structure. alternatively, finalization can be performed by obtaining the streaming ASN1 BIO directly using BIO_new_PKCS7(). so many options bestie, choose your fighter 🧚

PKCS7_encrypt() is similar to PKCS7_encrypt_ex() but uses default values of NULL for the library context libctx and the property query propq — it's the ✨low-effort, still-slaying✨ version.

⭐ RETURN VALUES ⭐

PKCS7_encrypt_ex() and PKCS7_encrypt() return either a PKCS7 structure or NULL if an error occurred 😔 the error can be obtained from ERR_get_error(3). go get your receipts.

💜 SEE ALSO 💜

ERR_get_error(3), PKCS7_decrypt(3) 🫶

🌸 HISTORY 🌸

• the function PKCS7_encrypt_ex() was added in OpenSSL 3.0 ✨
• the PKCS7_STREAM flag was added in OpenSSL 1.0.0 🎀

👑 COPYRIGHT 👑

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>.

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okay that's the whole page bestie, you ate that 🍓 this was OpenSSL 4.0.3, dated 2026-09-29, and yes the manual is literally called pkcs7_encrypt(3ssl) — go encrypt something, drink water, and stay iconic 💖✨💅