=pod

=head1 NAME

PKCS7_sign - create a PKCS#7 signedData structure

=head1 SYNOPSIS

PKCS7 *PKCS7_sign(X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs, BIO *data, int flags);

=head1 DESCRIPTION

PKCS7_sign() creates and returns a PKCS#7 signedData structure. B<signcert>
is the certificate to sign with, B<pkey> is the corresponsding private key.
B<certs> is an optional additional set of certificates to include in the
PKCS#7 structure (for example any intermediate CAs in the chain). 

The data to be signed is read from BIO B<data>.

B<flags> is an optional set of flags.

=head1 NOTES

Any of the following flags (ored together) can be passed in the B<flags> parameter.

Many S/MIME clients expect the signed content to include valid MIME headers. If
the B<PKCS7_TEXT> flag is set MIME headers for type B<text/plain> are prepended
to the data.

If B<PKCS7_NOCERTS> is set the signer's certificate will not be included in the
PKCS7 structure, the signer's certificate must still be supplied in the B<signcert>
parameter though. This can reduce the size of the signature if the signers certificate
can be obtained by other means: for example a previously signed message.

The data being signed is included in the PKCS7 structure, unless B<PKCS7_DETACHED> 
is set in which case it is omitted. This is used for PKCS7 detached signatures
which are used in S/MIME plaintext signed messages for example.

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.

The signedData structure includes several PKCS#7 autenticatedAttributes including
the signing time, the PKCS#7 content type and the supported list of ciphers in
an SMIMECapabilities attribute. If B<PKCS7_NOATTR> is set then no authenticatedAttributes
will be used. If B<PKCS7_NOSMIMECAP> is set then just the SMIMECapabilities are
omitted.

=head1 RETURN VALUES

PKCS7_sign() returns either a valid PKCS7 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)|ERR_get_error(3)>, L<PKCS7_verify(3)|PKCS7_verify(3)>

=head1 HISTORY

TBA

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