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.\" ========================================================================
.\"
.IX Title "PKCS7_encrypt 3"
.TH PKCS7_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"
PKCS7_encrypt \- create a PKCS#7 envelopedData structure
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/pkcs7.h>
\&
\& PKCS7 *PKCS7_encrypt(STACK_OF(X509) *certs, BIO *in, const EVP_CIPHER *cipher, int flags);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fIPKCS7_encrypt()\fR creates and returns a PKCS#7 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 \s-1RSA\s0 keys are supported in PKCS#7 and envelopedData so the recipient
certificates supplied to this function must all contain \s-1RSA\s0 public keys, though
they do not have to be signed using the \s-1RSA\s0 algorithm.
.PP
\&\fIEVP_des_ede3_cbc()\fR (triple \s-1DES\s0) is the algorithm of choice for S/MIME use
because most clients will support it.
.PP
Some old \*(L"export grade\*(R" clients may only support weak encryption using 40 or 64
bit \s-1RC2.\s0 These can be used by passing \fIEVP_rc2_40_cbc()\fR and \fIEVP_rc2_64_cbc()\fR
respectively.
.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
\&\fIPKCS7_encrypt()\fR.
.PP
The following flags can be passed in the \fBflags\fR parameter.
.PP
If the \fB\s-1PKCS7_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-1PKCS7_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-1PKCS7_BINARY\s0\fR is set then
\&\fB\s-1PKCS7_TEXT\s0\fR is ignored.
.PP
If the \fB\s-1PKCS7_STREAM\s0\fR flag is set a partial \fB\s-1PKCS7\s0\fR structure is output
suitable for streaming I/O: no data is read from the \s-1BIO \s0\fBin\fR.
.SH "NOTES"
.IX Header "NOTES"
If the flag \fB\s-1PKCS7_STREAM\s0\fR is set the returned \fB\s-1PKCS7\s0\fR structure is \fBnot\fR
complete and outputting its contents via a function that does not
properly finalize the \fB\s-1PKCS7\s0\fR structure will give unpredictable 
results.
.PP
Several functions including \fISMIME_write_PKCS7()\fR, \fIi2d_PKCS7_bio_stream()\fR,
\&\fIPEM_write_bio_PKCS7_stream()\fR finalize the structure. Alternatively finalization
can be performed by obtaining the streaming \s-1ASN1 \s0\fB\s-1BIO\s0\fR directly using
\&\fIBIO_new_PKCS7()\fR.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fIPKCS7_encrypt()\fR returns either a \s-1PKCS7\s0 structure or \s-1NULL\s0 if an error occurred.
The error can be obtained from \fIERR_get_error\fR\|(3).
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIERR_get_error\fR\|(3), \fIPKCS7_decrypt\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
\&\fIPKCS7_decrypt()\fR was added to OpenSSL 0.9.5
The \fB\s-1PKCS7_STREAM\s0\fR flag was first supported in OpenSSL 1.0.0.