PKCS7_sign(3)               OpenSSL               PKCS7_sign(3)





NAME
       PKCS7_sign - create a PKCS#7 signedData structure

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

DESCRIPTION
       PKCS7_sign() creates and returns a PKCS#7 signedData
       structure. signcert is the certificate to sign with,
       pkey is the corresponsding private key.  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 data.

       flags is an optional set of flags.

NOTES
       Any of the following flags (ored together) can be passed
       in the flags parameter.

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

       If 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 signcert
       parameter though. This can reduce the size of the signa-
       ture 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 struc-
       ture, unless 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 specifica-
       tions) if 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 auten-
       ticatedAttributes including the signing time, the PKCS#7
       content type and the supported list of ciphers in an
       SMIMECapabilities attribute. If PKCS7_NOATTR is set then
       no authenticatedAttributes will be used. If PKCS7_NOS-
       MIMECAP is set then just the SMIMECapabilities are omit-
       ted.

       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.

BUGS
       PKCS7_sign() is somewhat limited. It does not support
       multiple signers, some advanced attributes such as
       counter signatures are not supported.

       The SHA1 digest algorithm is currently always used.

       When the signed data is not detached it will be stored
       in memory within the PKCS7 structure. This effectively
       limits the size of messages which can be signed due to
       memory restraints. There should be a way to sign data
       without having to hold it all in memory, this would how-
       ever require fairly major revisions of the OpenSSL ASN1
       code.

       Clear text signing does not store the content in memory
       but the way PKCS7_sign() operates means that two passes
       of the data must typically be made: one to compute the
       signatures and a second to output the data along with
       the signature. There should be a way to process the data
       with only a single pass.

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).

SEE ALSO
       ERR_get_error(3), PKCS7_verify(3)

HISTORY
       PKCS7_sign() was added to OpenSSL 0.9.5



0.9.7c                     2002-10-09             PKCS7_sign(3)
