libressl-SMIME_read_PKCS7(3)

libressl-SMIME_read_PKCS73

Extract a pkcs#7 object from an s/mime message

Usage

Crypto Library (libcrypto, -lcrypto)

#include <openssl/pkcs7.h>

PKCS7 *

SMIME_read_PKCS7(BIO *in, BIO **bcont);

Overview

SMIME_read_PKCS7() parses a message in S/MIME format.

in is a BIO to read the message from.

If cleartext signing is used, then the content is saved in a memory BIO which is written to *bcont, otherwise *bcont is set to NULL.

The parsed PKCS#7 structure is returned, or NULL if an error occurred.

If *bcont is not NULL, then the message is clear text signed. *bcont can then be passed to PKCS7_verify(3) with the PKCS7_DETACHED flag set.

Otherwise the type of the returned structure can be determined using the PKCS7_type_is_*() macros defined in ⟨openssl/pkcs7.h⟩.

To support future functionality, if bcont is not NULL, *bcont should be initialized to NULL. For example:

BIO *cont = NULL;
PKCS7 *p7;
p7 = SMIME_read_PKCS7(in, &cont);

Return values

SMIME_read_PKCS7() returns a valid PKCS7 structure or NULL if an error occurred. The error can be obtained from ERR_get_error(3).

History

SMIME_read_PKCS7() first appeared in OpenSSL 0.9.5 and has been available since OpenBSD 2.7.

Bugs

The MIME parser used by SMIME_read_PKCS7() is somewhat primitive. While it will handle most S/MIME messages, more complex compound formats may not work.

The parser assumes that the PKCS7 structure is always base64 encoded, and it will not handle the case where it is in binary format or uses quoted printable format.

The use of a memory BIO to hold the signed content limits the size of the message which can be processed due to memory restraints: a streaming single pass option should be available.

From libressl 4.4.0-1 in Arch Linux 2026-11-01. Parsed by carta from the page's mdoc source.