OpenSL                                         dhparam(1openssl)



NAME
     dhparam - DH parameter manipulation and generation

SYNOPSIS
     openssl dhparam [-inform DERPEM] [-outform DERPEM] [-in
     filename] [-out filename] [-dsaparam] [-noout] [-text] [-C]
     [-2] [-5] [-rand file(s)] [-engine id] [numbits]

DESCRIPTION
     This command is used to manipulate DH parameter files.

OPTIONS
     -inform DERPEM
         This specifies the input format. The DER option uses an
         ASN1 DER encoded form compatible with the PKCS#3
         DHparameter structure. The PEM form is the default
         format: it consists of the DER format base64 encoded
         with additional header and footer lines.

     -outform DERPEM
         This specifies the output format, the options have the
         same meaning as the -inform option.

     -in filename
         This specifies the input filename to read parameters
         from or standard input if this option is not specified.

     -out filename
         This specifies the output filename parameters to.
         Standard output is used if this option is not present.
         The output filename should not be the same as the input
         filename.

     -dsaparam
         If this option is used, DSA rather than DH parameters
         are read or created; they are converted to DH format.
         Otherwise, "strong" primes (such that (p-1)/2 is also
         prime) will be used for DH parameter generation.

         DH parameter generation with the -dsaparam option is
         much faster, and the recommended exponent length is
         shorter, which makes DH key exchange more efficient.
         Beware that with such DSA-style DH parameters, a fresh
         DH key should be created for each use to avoid small-
         subgroup attacks that may be possible otherwise.

     -2, -5
         The generator to use, either 2 or 5. 2 is the default.
         If present then the input file is ignored and parameters
         are generated instead.

     -rand file(s)



OpenSL-0.9.8       Last change: Oct 11 2005                    1






OpenSL                                         dhparam(1openssl)



         a file or files containing random data used to seed the
         random number generator, or an EGD socket (see
         RANDegd(3)).  Multiple files can be specified separated
         by a OS-dependent character.  The separator is ; for
         MS-Windows, , for OpenVMS, and : for all others.

     numbits
         this option specifies that a parameter set should be
         generated of size numbits. It must be the last option.
         If not present then a value of 512 is used. If this
         option is present then the input file is ignored and
         parameters are generated instead.

     -noout
         this option inhibits the output of the encoded version
         of the parameters.

     -text
         this option prints out the DH parameters in human
         readable form.

     -C  this option converts the parameters into C code. The
         parameters can then be loaded by calling the
         getdhnumbits() function.

     -engine id
         specifying an engine (by it's unique id string) will
         cause req to attempt to obtain a functional reference to
         the specified engine, thus initialising it if needed.
         The engine will then be set as the default for all
         available algorithms.

WARNINGS
     The program dhparam combines the functionality of the
     programs dh and gendh in previous versions of OpenSL and
     SLeay. The dh and gendh programs are retained for now but
     may have different purposes in future versions of OpenSL.

NOTES
     PEM format DH parameters use the header and footer lines:

      -----BEGIN DH PARAMETERS-----
      -----END DH PARAMETERS-----

     OpenSL currently only supports the older PKCS#3 DH, not the
     newer X9.42 DH.

     This program manipulates DH parameters not keys.

BUGS
     There should be a way to generate and manipulate DH keys.




OpenSL-0.9.8       Last change: Oct 11 2005                    2






OpenSL                                         dhparam(1openssl)



SEE ALSO
     dsaparam(1)

HISTORY
     The dhparam command was added in OpenSL 0.9.5.  The
     -dsaparam option was added in OpenSL 0.9.6.

















































OpenSL-0.9.8       Last change: Oct 11 2005                    3