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.\" ========================================================================
.\"
.IX Title "CMS_ENCRYPT 3"
.TH CMS_ENCRYPT 3 "2023-09-11" "1.1.1w" "OpenSSL"
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
CMS_encrypt \- create a CMS envelopedData structure
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/cms.h>
\&
\& CMS_ContentInfo *CMS_encrypt(STACK_OF(X509) *certs, BIO *in,
\& const EVP_CIPHER *cipher, unsigned int flags);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fBCMS_encrypt()\fR creates and returns a \s-1CMS\s0 EnvelopedData structure. \fBcerts\fR
is a list of recipient certificates. \fBin\fR is the content to be encrypted.
\&\fBcipher\fR is the symmetric cipher to use. \fBflags\fR is an optional set of flags.
.SH "NOTES"
.IX Header "NOTES"
Only certificates carrying \s-1RSA,\s0 Diffie-Hellman or \s-1EC\s0 keys are supported by this
function.
.PP
\&\fBEVP_des_ede3_cbc()\fR (triple \s-1DES\s0) is the algorithm of choice for S/MIME use
because most clients will support it.
.PP
The algorithm passed in the \fBcipher\fR parameter must support \s-1ASN1\s0 encoding of
its parameters.
.PP
Many browsers implement a \*(L"sign and encrypt\*(R" 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 \s-1BIO\s0 and passing it to
\&\fBCMS_encrypt()\fR.
.PP
The following flags can be passed in the \fBflags\fR parameter.
.PP
If the \fB\s-1CMS_TEXT\s0\fR flag is set \s-1MIME\s0 headers for type \fBtext/plain\fR are
prepended to the data.
.PP
Normally the supplied content is translated into \s-1MIME\s0 canonical format (as
required by the S/MIME specifications) if \fB\s-1CMS_BINARY\s0\fR 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 \fB\s-1CMS_BINARY\s0\fR is set then
\&\fB\s-1CMS_TEXT\s0\fR is ignored.
.PP
OpenSSL will by default identify recipient certificates using issuer name
and serial number. If \fB\s-1CMS_USE_KEYID\s0\fR 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.
.PP
If the \fB\s-1CMS_STREAM\s0\fR flag is set a partial \fBCMS_ContentInfo\fR structure is
returned suitable for streaming I/O: no data is read from the \s-1BIO\s0 \fBin\fR.
.PP
If the \fB\s-1CMS_PARTIAL\s0\fR flag is set a partial \fBCMS_ContentInfo\fR structure is
returned to which additional recipients and attributes can be added before
finalization.
.PP
The data being encrypted is included in the CMS_ContentInfo structure, unless
\&\fB\s-1CMS_DETACHED\s0\fR is set in which case it is omitted. This is rarely used in
practice and is not supported by \fBSMIME_write_CMS()\fR.
.SH "NOTES"
.IX Header "NOTES"
If the flag \fB\s-1CMS_STREAM\s0\fR is set the returned \fBCMS_ContentInfo\fR structure is
\&\fBnot\fR complete and outputting its contents via a function that does not
properly finalize the \fBCMS_ContentInfo\fR structure will give unpredictable
results.
.PP
Several functions including \fBSMIME_write_CMS()\fR, \fBi2d_CMS_bio_stream()\fR,
\&\fBPEM_write_bio_CMS_stream()\fR finalize the structure. Alternatively finalization
can be performed by obtaining the streaming \s-1ASN1\s0 \fB\s-1BIO\s0\fR directly using
\&\fBBIO_new_CMS()\fR.
.PP
The recipients specified in \fBcerts\fR use a \s-1CMS\s0 KeyTransRecipientInfo info
structure. KEKRecipientInfo is also supported using the flag \fB\s-1CMS_PARTIAL\s0\fR
and \fBCMS_add0_recipient_key()\fR.
.PP
The parameter \fBcerts\fR may be \s-1NULL\s0 if \fB\s-1CMS_PARTIAL\s0\fR is set and recipients
added later using \fBCMS_add1_recipient_cert()\fR or \fBCMS_add0_recipient_key()\fR.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBCMS_encrypt()\fR returns either a CMS_ContentInfo structure or \s-1NULL\s0 if an error
occurred. The error can be obtained from \fBERR_get_error\fR\|(3).
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBERR_get_error\fR\|(3), \fBCMS_decrypt\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
The \fB\s-1CMS_STREAM\s0\fR flag was first supported in OpenSSL 1.0.0.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2008\-2018 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the OpenSSL license (the \*(L"License\*(R"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.