dhparam - DH parameter manipulation and generation


   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]


   This command is used to manipulate DH parameter files.


   -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.

       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 if the parameters are valid primes and generator.

   -2, -5
       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.

       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

       this option inhibits the output of the encoded version of the

       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.


   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.


   PEM format DH parameters use the header and footer lines:


    -----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.


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




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


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