PKCS7_ENCRYPT(3ossl)

okay bestie, welcome to PKCS7_ENCRYPT(3ossl) — the manual page for making a PKCS#7 envelopedData structure 💌 it's giving "crypto but make it group chat", and we're gonna get through it together, no cap.

✨ NAME ✨

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

🦋 SYNOPSIS 🦋

#include <openssl/pkcs7.h>

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

💖 DESCRIPTION 💖

okay so PKCS7_encrypt_ex() creates and returns a PKCS#7 envelopedData structure. slay. Here's the cast of characters:

• certs is a 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.
• libctx is the library context, and propq is the property query — both are used when retrieving algorithms from providers.

lowkey important: only RSA keys are supported in PKCS#7 and envelopedData, so the recipient certificates supplied to this function must all contain RSA public keys 😭 they do not have to be signed using the RSA algorithm, though.

EVP_des_ede3_cbc() (triple DES) is the algorithm of choice for S/MIME use because most clients will support it. iconic, honestly.

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. weak crypto warning, bestie — that's literally what the page says, so don't come for me.

The algorithm passed in the cipher parameter must support ASN1 encoding of its parameters. periodt.

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(). cute, right? 💅

The following flags can be passed in the flags parameter:

• PKCS7_TEXT — if this flag is set, MIME headers for type text/plain are prepended to the data.
• PKCS7_BINARY — 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.
• PKCS7_STREAM — if this flag is set, a partial PKCS7 structure is output suitable for streaming I/O: no data is read from the BIO in.

🚨 streaming caution 🚨 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. don't do that to yourself, bestie 😭

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, all valid 🫶

PKCS7_encrypt() is similar to PKCS7_encrypt_ex() but uses default values of NULL for the library context libctx and the property query propq.

🌈 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). if you get NULL, it's not a vibe — go check that error 💀

👑 SEE ALSO 👑

ERR_get_error(3), PKCS7_decrypt(3) — go read those too, iykyk 📚

🎀 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 2002-2020 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>.

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and that's the whole page, bestie ✨ this lil manual is from OpenSSL 3.5.6, dated 2026-04-07, and it's the PKCS7_ENCRYPT(3ossl) page — mwah 💋