.\"	$OpenBSD: PKCS7_encrypt.3,v 1.3 2016/11/24 19:45:16 jmc Exp $
.\"
.Dd $Mdocdate: November 24 2016 $
.Dt PKCS7_ENCRYPT 3
.Os
.Sh NAME
.Nm PKCS7_encrypt
.Nd create a PKCS#7 envelopedData structure
.Sh SYNOPSIS
.In openssl/pkcs7.h
.Ft PKCS7 *
.Fo PKCS7_encrypt
.Fa "STACK_OF(X509) *certs"
.Fa "BIO *in"
.Fa "const EVP_CIPHER *cipher"
.Fa "int flags"
.Fc
.Sh DESCRIPTION
.Fn PKCS7_encrypt
creates and returns a PKCS#7 envelopedData structure.
.Fa certs
is a list of recipient certificates.
.Fa in
is the content to be encrypted.
.Fa cipher
is the symmetric cipher to use.
.Fa flags
is an optional set of flags.
.Pp
Only RSA keys are supported in PKCS#7 and envelopedData so the recipient
certificates supplied to this function must all contain RSA public keys,
though they do not have to be signed using the RSA algorithm.
.Pp
The algorithm passed in the
.Fa cipher
parameter must support ASN.1 encoding of its parameters.
.Pp
Many browsers implement a "sign and encrypt" option which is simply an
S/MIME envelopedData containing an S/MIME signed message.
This can be readily produced by storing the S/MIME signed message in a
memory
.Vt BIO
and passing it to
.Fn PKCS7_encrypt .
.Pp
The following flags can be passed in the
.Fa flags
parameter.
.Pp
If the
.Dv PKCS7_TEXT
flag is set, MIME headers for type
.Sy text/plain
are prepended to the data.
.Pp
Normally the supplied content is translated into MIME canonical format
(as required by the S/MIME specifications).
If
.Dv PKCS7_BINARY
is set, no translation occurs.
This option should be used if the supplied data is in binary format;
otherwise, the translation will corrupt it.
If
.Dv PKCS7_BINARY
is set, then
.Dv PKCS7_TEXT
is ignored.
.Pp
If the
.Dv PKCS7_STREAM
flag is set, a partial
.Vt PKCS7
structure is output suitable for streaming I/O: no data is read from
.Fa in .
.Pp
If the flag
.Dv PKCS7_STREAM
is set, the returned
.Vt PKCS7
structure is
.Sy not
complete and outputting its contents via a function that does not
properly finalize the
.Vt PKCS7
structure will give unpredictable results.
.Pp
Several functions, including
.Xr SMIME_write_PKCS7 3 ,
.Xr i2d_PKCS7_bio_stream 3 ,
and
.Xr PEM_write_bio_PKCS7_stream 3 ,
finalize the structure.
Alternatively finalization can be performed by obtaining the streaming
ASN.1
.Vt BIO
directly using
.Xr BIO_new_PKCS7 3 .
.Sh RETURN VALUES
.Fn PKCS7_encrypt
returns either a
.Vt PKCS7
structure or
.Dv NULL
if an error occurred.
The error can be obtained from
.Xr ERR_get_error 3 .
.Sh SEE ALSO
.Xr ERR_get_error 3 ,
.Xr PKCS7_decrypt 3
.Sh HISTORY
.Xr PKCS7_decrypt 3
was added to OpenSSL 0.9.5.
The
.Dv PKCS7_STREAM
flag was first supported in OpenSSL 1.0.0.