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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
           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)
           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.

       -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
       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 PARAMETERS---------END
        -----END DH PARAMETERS-----OpenSSL PARAMETERS----OpenSSL

       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.



50                                               2013-03-05                                       DHPARAM(1)

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