text: =pod
  
  =head1 NAME
  
  PKCS7_sign - create a PKCS#7 signedData structure
  
  =head1 SYNOPSIS
  
   #include <openssl/pkcs7.h>
  
   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.
  
  If present the SMIMECapabilities attribute indicates support for the following
  algorithms: triple DES, 128 bit RC2, 64 bit RC2, DES and 40 bit RC2. If any of
  these algorithms is disabled then it will not be included.
  
  If the flags B<PKCS7_STREAM> is set then the returned B<PKCS7> structure is
  just initialized ready to perform the signing operation. The signing is however
  B<not> performed and the data to be signed is not read from the B<data>
  parameter. Signing is deferred until after the data has been written. In this
  way data can be signed in a single pass.
  
  If the B<PKCS7_PARTIAL> flag is set a partial B<PKCS7> structure is output to
  which additional signers and capabilities can be added before finalization.
  
  
  =head1 NOTES
  
  If the flag B<PKCS7_STREAM> is set the returned B<PKCS7> structure is B<not>
  complete and outputting its contents via a function that does not properly
  finalize the B<PKCS7> structure will give unpredictable results.
  
  Several functions including SMIME_write_PKCS7(), i2d_PKCS7_bio_stream(),
  PEM_write_bio_PKCS7_stream() finalize the structure. Alternatively finalization
  can be performed by obtaining the streaming ASN1 B<BIO> directly using
  BIO_new_PKCS7().
  
  If a signer is specified it will use the default digest for the signing
  algorithm. This is B<SHA1> for both RSA and DSA keys.
  
  In OpenSSL 1.0.0 the B<certs>, B<signcert> and B<pkey> parameters can all be
  B<NULL> if the B<PKCS7_PARTIAL> flag is set. One or more signers can be added
  using the function B<PKCS7_sign_add_signer()>. B<PKCS7_final()> must also be
  called to finalize the structure if streaming is not enabled. Alternative
  signing digests can also be specified using this method.
  
  In OpenSSL 1.0.0 if B<signcert> and B<pkey> are NULL then a certificates only
  PKCS#7 structure is output.
  
  In versions of OpenSSL before 1.0.0 the B<signcert> and B<pkey> parameters must
  B<NOT> be NULL.
  
  =head1 BUGS
  
  Some advanced attributes such as counter signatures are not supported.
  
  =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
  
  PKCS7_sign() was added to OpenSSL 0.9.5
  
  The B<PKCS7_PARTIAL> flag was added in OpenSSL 1.0.0
  
  The B<PKCS7_STREAM> flag was added in OpenSSL 1.0.0
  
  =cut
  