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.\" ========================================================================
.\"
.IX Title "CMS_encrypt 3"
.TH CMS_encrypt 3 2019-12-20 1.0.2u OpenSSL
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH NAME
.Vb 1
\& CMS_encrypt \- create a CMS envelopedData structure
.Ve
.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 CMS 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 RSA, Diffie-Hellman or EC keys are supported by this
function.
.PP
\&\fBEVP_des_ede3_cbc()\fR (triple DES) 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 ASN1 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 BIO and passing it to
\&\fBCMS_encrypt()\fR.
.PP
The following flags can be passed in the \fBflags\fR parameter.
.PP
If the \fBCMS_TEXT\fR flag is set MIME headers for type \fBtext/plain\fR are
prepended to the data.
.PP
Normally the supplied content is translated into MIME canonical format (as
required by the S/MIME specifications) if \fBCMS_BINARY\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 \fBCMS_BINARY\fR is set then
\&\fBCMS_TEXT\fR is ignored.
.PP
OpenSSL will by default identify recipient certificates using issuer name
and serial number. If \fBCMS_USE_KEYID\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 \fBCMS_STREAM\fR flag is set a partial \fBCMS_ContentInfo\fR structure is
returned suitable for streaming I/O: no data is read from the BIO \fBin\fR.
.PP
If the \fBCMS_PARTIAL\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
\&\fBCMS_DETACHED\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 \fBCMS_STREAM\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 ASN1 \fBBIO\fR directly using
\&\fBBIO_new_CMS()\fR.
.PP
The recipients specified in \fBcerts\fR use a CMS KeyTransRecipientInfo info
structure. KEKRecipientInfo is also supported using the flag \fBCMS_PARTIAL\fR
and \fBCMS_add0_recipient_key()\fR.
.PP
The parameter \fBcerts\fR may be NULL if \fBCMS_PARTIAL\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 NULL 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"
\&\fBCMS_decrypt()\fR was added to OpenSSL 0.9.8
The \fBCMS_STREAM\fR flag was first supported in OpenSSL 1.0.0.