.\" $OpenBSD: SMIME_read_CMS.3,v 1.7 2021/12/14 14:30:50 schwarze Exp $
.\" full merge up to: OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100
.\"
.\" This file was written by Dr. Stephen Henson <steve@openssl.org>.
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.Dd $Mdocdate: December 14 2021 $
.Dt SMIME_READ_CMS 3
.Os
.Sh NAME
.Nm SMIME_read_CMS
.Nd extract CMS ContentInfo from an S/MIME message
.Sh SYNOPSIS
.In openssl/cms.h
.Ft CMS_ContentInfo *
.Fo SMIME_read_CMS
.Fa "BIO *in"
.Fa "BIO **bcont"
.Fc
.Sh DESCRIPTION
.Fn SMIME_read_CMS
parses a message in S/MIME format from
.Fa in .
.Pp
If the message uses cleartext signing, the content is saved in a memory BIO
which is written to
.Pf * Fa bcont
and which can then be passed to
.Xr CMS_verify 3
with the
.Dv CMS_DETACHED
flag set.
Otherwise,
.Pf * Fa bcont
is set to
.Dv NULL
and the type of the returned structure can be determined using
.Xr CMS_get0_type 3 .
.Pp
To support future functionality if
.Fa bcont
is not
.Dv NULL ,
.Pf * Fa bcont
should be initialized to
.Dv NULL ,
for example:
.Bd -literal -offset indent
BIO *cont = NULL;
CMS_ContentInfo *cms = SMIME_read_CMS(in, &cont);
.Ed
.Sh RETURN VALUES
.Fn SMIME_read_CMS
returns a valid
.Vt CMS_ContentInfo
structure or
.Dv NULL
if an error occurred.
The error can be obtained from
.Xr ERR_get_error 3 .
.Sh SEE ALSO
.Xr CMS_ContentInfo_new 3 ,
.Xr CMS_decrypt 3 ,
.Xr CMS_get0_type 3 ,
.Xr CMS_verify 3 ,
.Xr d2i_CMS_ContentInfo 3 ,
.Xr SMIME_read_ASN1 3 ,
.Xr SMIME_write_CMS 3
.Sh HISTORY
.Fn SMIME_read_CMS
first appeared in OpenSSL 0.9.8h
and has been available since
.Ox 6.7 .
.Sh BUGS
The MIME parser used by
.Fn SMIME_read_CMS
is somewhat primitive.
While it will handle most S/MIME messages, more complex compound formats
may not work.
.Pp
The parser assumes that the
.Vt CMS_ContentInfo
structure is always base64 encoded and will not handle the case
where it is in binary format or uses quoted printable format.
.Pp
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.