SMIME_READ_PKCS7(3) | Library Functions Manual | SMIME_READ_PKCS7(3)

# NAME

`SMIME_read_PKCS7` — extract a PKCS#7 object from an S/MIME message

# SYNOPSIS

library “libcrypto”
`#include <openssl/pkcs7.h>`

PKCS7 *
`SMIME_read_PKCS7`(BIO *in, BIO **bcont);

# DESCRIPTION

`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).

# SEE ALSO

BIO_f_base64(3), BIO_new(3), PKCS7_new(3), SMIME_read_CMS(3), SMIME_text(3), SMIME_write_PKCS7(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.

June 11, 2025 | Debian