path: root/src/lib/libcrypto/man/SMIME_write_CMS.3

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.Dd $Mdocdate: June 11 2025 $
.Dt SMIME_WRITE_CMS 3
.Os
.Sh NAME
.Nm SMIME_write_CMS
.Nd convert CMS structure to S/MIME format
.Sh SYNOPSIS
.Lb libcrypto
.In openssl/cms.h
.Ft int
.Fo SMIME_write_CMS
.Fa "BIO *out"
.Fa "CMS_ContentInfo *cms"
.Fa "BIO *data"
.Fa "int flags"
.Fc
.Sh DESCRIPTION
.Fn SMIME_write_CMS
generates an S/MIME message on
.Fa out
by writing MIME 1.0 headers
followed by a BER- and base64-encoded serialization of
.Fa cms .
The BER encoding uses the DER format except as described for
.Dv CMS_STREAM
below.
If streaming is enabled, the content must be supplied in the
.Fa data
argument.
.Pp
The
.Fa flags
can be the logical OR of zero or more of the following bits:
.Bl -tag -width Ds
.It Dv CMS_DETACHED
Use cleartext signing and generate a
.Qq multipart/signed
S/MIME message.
The content is read from
.Fa data .
If
.Fa data
is a
.Dv NULL
pointer, this flag is ignored.
.Pp
This flag is only supported if
.Fa cms
is of the type
.Vt SignedData
and
.Dv CMS_DETACHED
was also set when it was created with
.Xr CMS_sign 3 .
.Pp
If
.Dv CMS_STREAM
is not set, the data must be read twice:
once to compute the signature in
.Xr CMS_sign 3
and once to output the S/MIME message.
.Pp
If
.Dv CMS_DETACHED
is ignored or not specified, the smime-type is chosen according to
.Xr CMS_get0_type 3 :
.Bl -tag -width Ds
.It Dv NID_pkcs7_enveloped
.Qq enveloped-data
.It Dv NID_pkcs7_signed
.Bl -tag -width Msigned-receiptM -compact
.It Qq signed-receipt
if
.Xr CMS_get0_eContentType 3
is
.Dv NID_id_smime_ct_receipt
.It Qq signed-data
if
.Fa cms
specifies any digest algorithm
.It Qq certs-only
otherwise
.El
.It Dv NID_id_smime_ct_compressedData
.Qq compressed-data
.El
.It Dv CMS_REUSE_DIGEST
Skip the calls to
.Xr CMS_dataInit 3
and
.Xr CMS_dataFinal 3 .
This flag has no effect unless
.Dv CMS_DETACHED
is also set.
.It Dv CMS_STREAM
Perform streaming by reading the content from
.Fa data .
This only works if
.Dv CMS_DETACHED
is not specified.
.Pp
This flag should only be set if
.Dv CMS_STREAM
was also passed to the function that created
.Fa cms .
.Pp
The content is output in BER format using indefinite length
constructed encoding except in the case of
.Vt SignedData
with detached content where the content is absent and DER format is
used.
.It Dv CMS_TEXT
Prepend the line
.Qq Content-Type: text/plain
to the content.
This only makes sense if
.Dv CMS_DETACHED
is also set.
It is ignored if the flag
.Dv SMIME_BINARY
is also set.
.It Dv SMIME_BINARY
If specified, this flag is passed through to
.Xr SMIME_crlf_copy 3 .
.It Dv SMIME_CRLFEOL
End MIME header lines with pairs of carriage return and newline characters.
By default, no carriage return characters are written
and header lines are ended with newline characters only.
.El
.Sh RETURN VALUES
.Fn SMIME_write_CMS
is intended to return 1 on success or 0 on failure.
.Sh SEE ALSO
.Xr BIO_f_base64 3 ,
.Xr BIO_new 3 ,
.Xr CMS_ContentInfo_new 3 ,
.Xr CMS_encrypt 3 ,
.Xr CMS_sign 3 ,
.Xr d2i_CMS_ContentInfo 3 ,
.Xr ERR_get_error 3 ,
.Xr SMIME_crlf_copy 3 ,
.Xr SMIME_read_CMS 3 ,
.Xr SMIME_write_PKCS7 3
.Sh HISTORY
.Fn SMIME_write_CMS
first appeared in OpenSSL 0.9.8h
and has been available since
.Ox 6.7 .
.Sh BUGS
.Fn SMIME_write_CMS
ignores most errors and is likely to return 1
even after producing corrupt or incomplete output.
.Pp
.Fn SMIME_write_CMS
always base64 encodes CMS structures.
There should be an option to disable this.