genpkey - generate a private key
openssl genpkey [-out filename] [-outform PEM|DER] [-pass arg] [-cipher] [-engine id] [-paramfile file] [-algorithm alg] [-pkeyopt opt:value] [-genparam] [-text]
GENPKEY(1openssl) OpenSSL GENPKEY(1openssl)
NAME
openssl-genpkey, genpkey - generate a private key
SYNOPSIS
openssl genpkey [-out filename] [-outform PEM|DER] [-pass arg]
[-cipher] [-engine id] [-paramfile file] [-algorithm alg] [-pkeyopt
opt:value] [-genparam] [-text]
DESCRIPTION
The genpkey command generates a private key.
OPTIONS
-out filename
the output filename. If this argument is not specified then
standard output is used.
-outform DER|PEM
This specifies the output format DER or PEM. The default format is
PEM.
-pass arg
The output file password source. For more information about the
format of arg see the PASS PHRASE ARGUMENTS section in openssl(1).
-cipher
This option encrypts the private key with the supplied cipher. Any
algorithm name accepted by EVP_get_cipherbyname() is acceptable
such as des3.
-engine id
Specifying an engine (by its unique id string) will cause genpkey
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. If used this option
should precede all other options.
-algorithm alg
Public key algorithm to use such as RSA, DSA or DH. If used this
option must precede any -pkeyopt options. The options -paramfile
and -algorithm are mutually exclusive. Engines may add algorithms
in addition to the standard built-in ones.
Valid built-in algorithm names for private key generation are RSA
and EC.
Valid built-in algorithm names for parameter generation (see the
-genparam option) are DH, DSA and EC.
Note that the algorithm name X9.42 DH may be used as a synonym for
the DH algorithm. These are identical and do not indicate the type
of parameters that will be generated. Use the dh_paramgen_type
option to indicate whether PKCS#3 or X9.42 DH parameters are
required. See "DH Parameter Generation Options" below for more
details.
-pkeyopt opt:value
Set the public key algorithm option opt to value. The precise set
of options supported depends on the public key algorithm used and
its implementation. See "KEY GENERATION OPTIONS" and "PARAMETER
GENERATION OPTIONS" below for more details.
-genparam
Generate a set of parameters instead of a private key. If used this
option must precede any -algorithm, -paramfile or -pkeyopt options.
-paramfile filename
Some public key algorithms generate a private key based on a set of
parameters. They can be supplied using this option. If this option
is used the public key algorithm used is determined by the
parameters. If used this option must precede and -pkeyopt options.
The options -paramfile and -algorithm are mutually exclusive.
-text
Print an (unencrypted) text representation of private and public
keys and parameters along with the PEM or DER structure.
KEY GENERATION OPTIONS
The options supported by each algorith and indeed each implementation
of an algorithm can vary. The options for the OpenSSL implementations
are detailed below.
RSA Key Generation Options
rsa_keygen_bits:numbits
The number of bits in the generated key. If not specified 2048 is
used.
rsa_keygen_pubexp:value
The RSA public exponent value. This can be a large decimal or
hexadecimal value if preceded by 0x. Default value is 65537.
EC Key Generation Options
The EC key generation options can also be used for parameter
generation.
ec_paramgen_curve:curve
The EC curve to use. OpenSSL supports NIST curve names such as
"P-256".
ec_param_enc:encoding
The encoding to use for parameters. The "encoding" parameter must
be either "named_curve" or "explicit". The default value is
"named_curve".
PARAMETER GENERATION OPTIONS
The options supported by each algorithm and indeed each implementation
of an algorithm can vary. The options for the OpenSSL implementations
are detailed below.
DSA Parameter Generation Options
dsa_paramgen_bits:numbits
The number of bits in the generated prime. If not specified 2048 is
used.
dsa_paramgen_q_bits:numbits
The number of bits in the q parameter. Must be one of 160, 224 or
256. If not specified 224 is used.
dsa_paramgen_md:digest
The digest to use during parameter generation. Must be one of sha1,
sha224 or sha256. If set, then the number of bits in q will match
the output size of the specified digest and the dsa_paramgen_q_bits
parameter will be ignored. If not set, then a digest will be used
that gives an output matching the number of bits in q, i.e. sha1 if
q length is 160, sha224 if it 224 or sha256 if it is 256.
DH Parameter Generation Options
dh_paramgen_prime_len:numbits
The number of bits in the prime parameter p. The default is 2048.
dh_paramgen_subprime_len:numbits
The number of bits in the sub prime parameter q. The default is 256
if the prime is at least 2048 bits long or 160 otherwise. Only
relevant if used in conjunction with the dh_paramgen_type option to
generate X9.42 DH parameters.
dh_paramgen_generator:value
The value to use for the generator g. The default is 2.
dh_paramgen_type:value
The type of DH parameters to generate. Use 0 for PKCS#3 DH and 1
for X9.42 DH. The default is 0.
dh_rfc5114:num
If this option is set, then the appropriate RFC5114 parameters are
used instead of generating new parameters. The value num can take
the values 1, 2 or 3 corresponding to RFC5114 DH parameters
consisting of 1024 bit group with 160 bit subgroup, 2048 bit group
with 224 bit subgroup and 2048 bit group with 256 bit subgroup as
mentioned in RFC5114 sections 2.1, 2.2 and 2.3 respectively. If
present this overrides all other DH parameter options.
EC Parameter Generation Options
The EC parameter generation options are the same as for key generation.
See "EC Key Generation Options" above.
GOST2001 KEY GENERATION AND PARAMETER OPTIONS
Gost 2001 support is not enabled by default. To enable this algorithm,
one should load the ccgost engine in the OpenSSL configuration file.
See README.gost file in the engines/ccgost directiry of the source
distribution for more details.
Use of a parameter file for the GOST R 34.10 algorithm is optional.
Parameters can be specified during key generation directly as well as
during generation of parameter file.
paramset:name
Specifies GOST R 34.10-2001 parameter set according to RFC 4357.
Parameter set can be specified using abbreviated name, object short
name or numeric OID. Following parameter sets are supported:
paramset OID Usage
A 1.2.643.2.2.35.1 Signature
B 1.2.643.2.2.35.2 Signature
C 1.2.643.2.2.35.3 Signature
XA 1.2.643.2.2.36.0 Key exchange
XB 1.2.643.2.2.36.1 Key exchange
test 1.2.643.2.2.35.0 Test purposes
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
+---------------+--------------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+--------------------------+
|Availability | library/security/openssl |
+---------------+--------------------------+
|Stability | Pass-through uncommitted |
+---------------+--------------------------+
NOTES
The use of the genpkey program is encouraged over the algorithm
specific utilities because additional algorithm options and ENGINE
provided algorithms can be used.
Source code for open source software components in Oracle Solaris can
be found at https://www.oracle.com/downloads/opensource/solaris-source-
code-downloads.html.
This software was built from source available at
https://github.com/oracle/solaris-userland. The original community
source was downloaded from
https://www.openssl.org/source/openssl-1.0.2ze.tar.gz.
Further information about this software can be found on the open source
community website at https://www.openssl.org/.
EXAMPLES
Generate an RSA private key using default parameters:
openssl genpkey -algorithm RSA -out key.pem
Encrypt output private key using 128 bit AES and the passphrase
"hello":
openssl genpkey -algorithm RSA -out key.pem -aes-128-cbc -pass pass:hello
Generate a 2048 bit RSA key using 3 as the public exponent:
openssl genpkey -algorithm RSA -out key.pem -pkeyopt rsa_keygen_bits:2048 \
-pkeyopt rsa_keygen_pubexp:3
Generate 2048 bit DSA parameters:
openssl genpkey -genparam -algorithm DSA -out dsap.pem \
-pkeyopt dsa_paramgen_bits:2048
Generate DSA key from parameters:
openssl genpkey -paramfile dsap.pem -out dsakey.pem
Generate 2048 bit DH parameters:
openssl genpkey -genparam -algorithm DH -out dhp.pem \
-pkeyopt dh_paramgen_prime_len:2048
Generate 2048 bit X9.42 DH parameters:
openssl genpkey -genparam -algorithm DH -out dhpx.pem \
-pkeyopt dh_paramgen_prime_len:2048 \
-pkeyopt dh_paramgen_type:1
Output RFC5114 2048 bit DH parameters with 224 bit subgroup:
openssl genpkey -genparam -algorithm DH -out dhp.pem -pkeyopt dh_rfc5114:2
Generate DH key from parameters:
openssl genpkey -paramfile dhp.pem -out dhkey.pem
Generate EC key directly:
openssl genpkey -algorithm EC -out eckey.pem \
-pkeyopt ec_paramgen_curve:P-384 \
-pkeyopt ec_param_enc:named_curve
HISTORY
The ability to use NIST curve names, and to generate an EC key
directly, were added in OpenSSL 1.0.2.
1.0.2ze 2022-05-03 GENPKEY(1openssl)