path: root/src/lib/libcrypto/man/SMIME_write_PKCS7.3

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.Dd $Mdocdate: June 11 2025 $
.Dt SMIME_WRITE_PKCS7 3
.Os
.Sh NAME
.Nm SMIME_write_PKCS7
.Nd convert PKCS#7 structure to S/MIME format
.Sh SYNOPSIS
.Lb libcrypto
.In openssl/pkcs7.h
.Ft int
.Fo SMIME_write_PKCS7
.Fa "BIO *out"
.Fa "PKCS7 *p7"
.Fa "BIO *data"
.Fa "int flags"
.Fc
.Sh DESCRIPTION
.Fn SMIME_write_PKCS7
generates an S/MIME message on
.Fa out
by writing MIME 1.0 headers
followed by a BER- and base64-encoded serialization of
.Fa p7 .
The BER encoding uses the DER format except as described for
.Dv PKCS7_STREAM
below.
If streaming is enabled, then 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 PKCS7_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 for signedData where
.Dv PKCS7_DETACHED
is also set when
.Xr PKCS7_sign 3
is called.
.Pp
If
.Dv PKCS7_STREAM
is not set, the data must be read twice: once to compute the
signature in
.Xr PKCS7_sign 3
and once to output the S/MIME message.
.Pp
If
.Dv PKCS7_DETACHED
is ignored or not specified, the smime-type is chosen according to the type of
.Fa p7 :
.Bl -tag -width Ds
.It Dv NID_pkcs7_enveloped
.Qq enveloped-data
.It Dv NID_pkcs7_signed
.Bl -tag -width Msigned-dataM -compact
.It Qq signed-data
if
.Fa p7
specifies any digest algorithm
.It Qq certs-only
otherwise
.El
.It Dv NID_id_smime_ct_compressedData
.Qq compressed-data
.El
.It Dv PKCS7_REUSE_DIGEST
Skip the calls to
.Xr PKCS7_dataInit 3
and
.Xr PKCS7_dataFinal 3 .
This flag has no effect unless
.Dv PKCS7_DETACHED
is also set.
.It Dv PKCS7_STREAM
Perform streaming by reading the content from
.Fa data .
This only works if
.Dv PKCS7_DETACHED
is not specified.
.Pp
This flag should only be set if
.Dv PKCS7_STREAM
was also set in the previous call to
.Xr PKCS7_sign 3
or
.Xr PKCS7_encrypt 3 .
.Pp
The content is output in BER format using indefinite length constructed
encoding except in the case of signed data with detached content
where the content is absent and DER format is used.
.It Dv PKCS7_TEXT
Prepend the line
.Qq Content-Type: text/plain
to the content.
This only makes sense if
.Dv PKCS7_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.
.It Dv SMIME_OLDMIME
If this bit is set in the
.Fa flags
argument,
.Qq application/pkcs7-mime
or
.Qq application/pkcs7-signature
is used in Content-Type headers.
Otherwise,
.Qq application/x-pkcs7-mime
or
.Qq application/x-pkcs7-signature
is used.
.El
.Sh RETURN VALUES
.Fn SMIME_write_PKCS7
is intended to return 1 on success or 0 on failure.
.Sh SEE ALSO
.Xr BIO_f_base64 3 ,
.Xr BIO_new 3 ,
.Xr i2d_PKCS7_bio_stream 3 ,
.Xr PEM_write_bio_PKCS7_stream 3 ,
.Xr PEM_write_PKCS7 3 ,
.Xr PKCS7_final 3 ,
.Xr PKCS7_new 3 ,
.Xr SMIME_crlf_copy 3 ,
.Xr SMIME_read_PKCS7 3 ,
.Xr SMIME_write_CMS 3
.Sh HISTORY
.Fn SMIME_write_PKCS7
first appeared in OpenSSL 0.9.5 and has been available since
.Ox 2.7 .
.Sh BUGS
.Fn SMIME_write_PKCS7
ignores most errors and is likely to return 1
even after producing corrupt or incomplete output.
.Pp
.Fn SMIME_write_PKCS7
always base64 encodes PKCS#7 structures.
There should be an option to disable this.