DHPARAM(1ssl)
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 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
HISTORY
- The dhparam command was added in OpenSSL 0.9.5. The -dsaparam option
was added in OpenSSL 0.9.6.