dhparam(1)

     DHPARAM(1)             0.9.6h (2000-04-12)             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)] [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 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)

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     DHPARAM(1)             0.9.6h (2000-04-12)             DHPARAM(1)

              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 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
              get_dhnumbits() function.

     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.

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