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 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 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 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 PKCS7_NOATTR is set then no
          authenticatedAttributes will be used. If 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.

     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 however 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