/usr/man/cat.1/openssl-dhparam.1

DHPARAM(1)                   OpenSSL                   DHPARAM(1)

NAME

     openssl-dhparam, dhparam - DH parameter manipulation and
     generation

SYNOPSIS

     openssl dhparam [-inform DER|PEM] [-outform DER|PEM] [-in
     filename] [-out filename] [-dsaparam] [-check] [-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 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.

     -check
         check if the parameters are valid primes and generator.

     -2, -5

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DHPARAM(1)                   OpenSSL                   DHPARAM(1)

         The generator to use, either 2 or 5. If present then the
         input file is ignored and parameters are generated
         instead. If not present but numbits is present,
         parameters are generated with the default generator 2.

     -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 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 this option is present then the input file is ignored
         and parameters are generated instead. If this option is
         not present but a generator (-2 or -5) is present,
         parameters are generated with a default length of 2048
         bits.

     -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.

     -engine id
         specifying an engine (by its unique id string) will
         cause dhparam 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 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-----

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DHPARAM(1)                   OpenSSL                   DHPARAM(1)

     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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See also dhparam(1)