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=head1 NAME

PKCS7_encrypt - create a PKCS#7 envelopedData structure

=head1 SYNOPSIS

 #include <openssl/pkcs7.h>

 PKCS7 *PKCS7_encrypt(STACK_OF(X509) *certs, BIO *in, const EVP_CIPHER *cipher, int flags);

=head1 DESCRIPTION

PKCS7_encrypt() creates and returns a PKCS#7 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 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.

EVP_des_ede3_cbc() (triple DES) is the algorithm of choice for S/MIME use because
most clients will support it.

Some old "export grade" clients may only support weak encryption using 40 or 64 bit
RC2. These can be used by passing EVP_rc2_40_cbc() and EVP_rc2_64_cbc() respectively.

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
PKCS7_encrypt().

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

If the B<PKCS7_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<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 B<PKCS7_BINARY> is set then B<PKCS7_TEXT> is ignored.

=head1 RETURN VALUES

PKCS7_encrypt() returns either a valid PKCS7 structure or NULL if an error occurred.
The error can be obtained from ERR_get_error(3).

=head1 BUGS

The lack of single pass processing and need to hold all data in memory as
mentioned in PKCS7_sign() also applies to PKCS7_verify().

=head1 SEE ALSO

L<ERR_get_error(3)|ERR_get_error(3)>, L<PKCS7_decrypt(3)|PKCS7_decrypt(3)>

=head1 HISTORY

PKCS7_decrypt() was added to OpenSSL 0.9.5

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