=pod

=head1 NAME

CMS_encrypt - create a CMS envelopedData structure

=head1 SYNOPSIS

 #include <openssl/cms.h>

 CMS_ContentInfo *CMS_encrypt(STACK_OF(X509) *certs, BIO *in,

                              const EVP_CIPHER *cipher, unsigned int flags);

=head1 DESCRIPTION

CMS_encrypt() creates and returns a CMS EnvelopedData structure. B<certs>

is a list of recipient certificates. B<in> is the content to be encrypted.

B<cipher> is the symmetric cipher to use. B<flags> is an optional set of flags.

=head1 NOTES

Only certificates carrying RSA, Diffie-Hellman or EC keys are supported by this

function.

EVP_des_ede3_cbc() (triple DES) is the algorithm of choice for S/MIME use

because most clients will support it.

The algorithm passed in the B<cipher> parameter must support ASN1 encoding of

its parameters.

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 BIO and passing it to

CMS_encrypt().

The following flags can be passed in the B<flags> parameter.

If the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are

prepended to the data.

Normally the supplied content is translated into MIME canonical format (as

required by the S/MIME specifications) if B<CMS_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 B<CMS_BINARY> is set then

B<CMS_TEXT> is ignored.

OpenSSL will by default identify recipient certificates using issuer name

and serial number. If B<CMS_USE_KEYID> is set it will use the subject key

identifier value instead. An error occurs if all recipient certificates do not

have a subject key identifier extension.

If the B<CMS_STREAM> flag is set a partial B<CMS_ContentInfo> structure is

returned suitable for streaming I/O: no data is read from the BIO B<in>.

If the B<CMS_PARTIAL> flag is set a partial B<CMS_ContentInfo> structure is

returned to which additional recipients and attributes can be added before

finalization.

The data being encrypted is included in the CMS_ContentInfo structure, unless

B<CMS_DETACHED> is set in which case it is omitted. This is rarely used in

practice and is not supported by SMIME_write_CMS().

=head1 NOTES

If the flag B<CMS_STREAM> is set the returned B<CMS_ContentInfo> structure is

B<not> complete and outputting its contents via a function that does not

properly finalize the B<CMS_ContentInfo> structure will give unpredictable

results.

Several functions including SMIME_write_CMS(), i2d_CMS_bio_stream(),

PEM_write_bio_CMS_stream() finalize the structure. Alternatively finalization

can be performed by obtaining the streaming ASN1 B<BIO> directly using

BIO_new_CMS().

The recipients specified in B<certs> use a CMS KeyTransRecipientInfo info

structure. KEKRecipientInfo is also supported using the flag B<CMS_PARTIAL>

and CMS_add0_recipient_key().

The parameter B<certs> may be NULL if B<CMS_PARTIAL> is set and recipients

added later using CMS_add1_recipient_cert() or CMS_add0_recipient_key().

=head1 RETURN VALUES

CMS_encrypt() returns either a CMS_ContentInfo structure or NULL if an error

occurred. The error can be obtained from ERR_get_error(3).

=head1 SEE ALSO

L<ERR_get_error(3)>, L<CMS_decrypt(3)>

=head1 HISTORY

The B<CMS_STREAM> flag was first supported in OpenSSL 1.0.0.

=head1 COPYRIGHT

Copyright 2008-2018 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the "License").  You may not use

this file except in compliance with the License.  You can obtain a copy

in the file LICENSE in the source distribution or at

L<https://www.openssl.org/source/license.html>.

=cut