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CentOS 7.0 - man page for dhparam (centos section 1)

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 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-----

       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.

1.0.1e					    2013-02-11				       DHPARAM(1)


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