DHPARAM(1)                  OpenSSL                  DHPARAM(1)





NAME
       dhparam - DH parameter manipulation and generation

SYNOPSIS
       openssl dhparam [-inform DER|PEM] [-outform DER|PEM]
       [-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 DER|PEM
           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 DER|PEM
           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 speci-
           fied.

       -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 parame-
           ters 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 other-
           wise.

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

       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 ver-
           sion 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
           get_dhnumbits() function.

       -engine id
           specifying an engine (by it's unique id string) will
           cause req to attempt to obtain a functional refer-
           ence 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 OpenSSL
       and SSLeay. The dh and gendh programs are retained for
       now but may have different purposes in future versions
       of OpenSSL.

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

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

       OpenSSL 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.

SEE ALSO
       dsaparam(1)

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



0.9.7c                     2003-01-30                DHPARAM(1)
