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.
