OPENSSL-GENPKEY(1SSL) OpenSSL OPENSSL-GENPKEY(1SSL)
NAME
openssl-genpkey - generate a private key
SYNOPSIS
openssl genpkey [-help] [-out filename] [-outform DER|PEM] [-quiet]
[-pass arg] [-cipher] [-paramfile file] [-algorithm alg] [-pkeyopt
opt:value] [-genparam] [-text] [-engine id] [-provider name]
[-provider-path path] [-propquery propq] [-config configfile]
DESCRIPTION
This command generates a private key.
OPTIONS
-help
Print out a usage message.
-out filename
Output the key to the specified file. If this argument is not
specified then standard output is used.
-outform DER|PEM
The output format, except when -genparam is given; the default is
PEM. See openssl-format-options(1) for details.
When -genparam is given, -outform is ignored.
-quiet
Do not output "status dots" while generating keys.
-pass arg
The output file password source. For more information about the
format of arg see openssl-passphrase-options(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.
-algorithm alg
Public key algorithm to use such as RSA, DSA, DH or DHX. 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,
RSA-PSS, EC, X25519, X448, ED25519 and ED448.
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
DHX keys and PKCS#3 refers to DH Keys. Some options are not shared
between DH and DHX keys.
-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 any -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.
-engine id
See "Engine Options" in openssl(1). This option is deprecated.
-provider name
-provider-path path
-propquery propq
See "Provider Options" in openssl(1), provider(7), and property(7).
-config configfile
See "Configuration Option" in openssl(1).
KEY 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. There are no key generation options defined for the
X25519, X448, ED25519 or ED448 algorithms.
RSA Key Generation Options
rsa_keygen_bits:numbits
The number of bits in the generated key. If not specified 2048 is
used.
rsa_keygen_primes:numprimes
The number of primes in the generated key. If not specified 2 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.
RSA-PSS Key Generation Options
Note: by default an RSA-PSS key has no parameter restrictions.
rsa_keygen_bits:numbits, rsa_keygen_primes:numprimes,
rsa_keygen_pubexp:value
These options have the same meaning as the RSA algorithm.
rsa_pss_keygen_md:digest
If set the key is restricted and can only use digest for signing.
rsa_pss_keygen_mgf1_md:digest
If set the key is restricted and can only use digest as it's MGF1
parameter.
rsa_pss_keygen_saltlen:len
If set the key is restricted and len specifies the minimum salt
length.
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.
DH Key Generation Options
group:name
The paramfile option is not required if a named group is used here.
See the "DH Parameter Generation Options" section below.
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
qbits: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
digest: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.
properties:query
The digest property query string to use when fetching a digest from
a provider.
type:type
The type of generation to use. Set this to 1 to use legacy
FIPS186-2 parameter generation. The default of 0 uses FIPS186-4
parameter generation.
gindex:index
The index to use for canonical generation and verification of the
generator g. Set this to a positive value ranging from 0..255 to
use this mode. Larger values will only use the bottom byte. This
index must then be reused during key validation to verify the value
of g. If this value is not set then g is not verifiable. The
default value is -1.
hexseed:seed
The seed seed data to use instead of generating a random seed
internally. This should be used for testing purposes only. This
will either produced fixed values for the generated parameters OR
it will fail if the seed did not generate valid primes.
DH Parameter Generation Options
For most use cases it is recommended to use the group option rather
than the type options. Note that the group option is not used by
default if no parameter generation options are specified.
group:name
dh_param:name
Use a named DH group to select constant values for the DH
parameters. All other options will be ignored if this value is
set.
Valid values that are associated with the algorithm of "DH" are:
"ffdhe2048", "ffdhe3072", "ffdhe4096", "ffdhe6144", "ffdhe8192",
"modp_1536", "modp_2048", "modp_3072", "modp_4096", "modp_6144",
"modp_8192".
Valid values that are associated with the algorithm of "DHX" are
the RFC5114 names "dh_1024_160", "dh_2048_224", "dh_2048_256".
dh_rfc5114:num
If this option is set, then the appropriate RFC5114 parameters are
used instead of generating new parameters. The value num can be one
of 1, 2 or 3 that are equivalent to using the option group with one
of "dh_1024_160", "dh_2048_224" or "dh_2048_256". All other
options will be ignored if this value is set.
pbits:numbits
dh_paramgen_prime_len:numbits
The number of bits in the prime parameter p. The default is 2048.
qbits:numbits
dh_paramgen_subprime_len:numbits
The number of bits in the sub prime parameter q. The default is
224. Only relevant if used in conjunction with the
dh_paramgen_type option to generate DHX parameters.
safeprime-generator:value
dh_paramgen_generator:value
The value to use for the generator g. The default is 2. The
algorithm option must be "DH" for this parameter to be used.
type:string
The type name of DH parameters to generate. Valid values are:
"generator"
Use a safe prime generator with the option safeprime_generator
The algorithm option must be "DH".
"fips186_4"
FIPS186-4 parameter generation. The algorithm option must be
"DHX".
"fips186_2"
FIPS186-4 parameter generation. The algorithm option must be
"DHX".
"group"
Can be used with the option pbits to select one of "ffdhe2048",
"ffdhe3072", "ffdhe4096", "ffdhe6144" or "ffdhe8192". The
algorithm option must be "DH".
"default"
Selects a default type based on the algorithm. This is used by
the OpenSSL default provider to set the type for backwards
compatibility. If algorithm is "DH" then "generator" is used.
If algorithm is "DHX" then "fips186_2" is used.
dh_paramgen_type:value
The type of DH parameters to generate. Valid values are 0, 1, 2 or
3 which correspond to setting the option type to "generator",
"fips186_2", "fips186_4" or "group".
digest:digest
The digest to use during parameter generation. Must be one of sha1,
sha224 or sha256. If set, then the number of bits in qbits will
match the output size of the specified digest and the qbits
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 is 224 or sha256 if it is 256. This
is only used by "fips186_4" and "fips186_2" key generation.
properties:query
The digest property query string to use when fetching a digest from
a provider. This is only used by "fips186_4" and "fips186_2" key
generation.
gindex:index
The index to use for canonical generation and verification of the
generator g. Set this to a positive value ranging from 0..255 to
use this mode. Larger values will only use the bottom byte. This
index must then be reused during key validation to verify the value
of g. If this value is not set then g is not verifiable. The
default value is -1. This is only used by "fips186_4" and
"fips186_2" key generation.
hexseed:seed
The seed seed data to use instead of generating a random seed
internally. This should be used for testing purposes only. This
will either produced fixed values for the generated parameters OR
it will fail if the seed did not generate valid primes. This is
only used by "fips186_4" and "fips186_2" key generation.
EC Parameter Generation Options
The EC parameter generation options are the same as for key generation.
See "EC Key Generation Options" above.
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.
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 that can be validated: The output
values for gindex and seed are required for key validation purposes and
are not saved to the output pem file).
openssl genpkey -genparam -algorithm DSA -out dsap.pem -pkeyopt pbits:2048 \
-pkeyopt qbits:224 -pkeyopt digest:SHA256 -pkeyopt gindex:1 -text
Generate DSA key from parameters:
openssl genpkey -paramfile dsap.pem -out dsakey.pem
Generate 4096 bit DH Key using safe prime group ffdhe4096:
openssl genpkey -algorithm DH -out dhkey.pem -pkeyopt group:ffdhe4096
Generate 2048 bit X9.42 DH key with 256 bit subgroup using RFC5114
group3:
openssl genpkey -algorithm DHX -out dhkey.pem -pkeyopt dh_rfc5114:3
Generate a DH key using a DH parameters file:
openssl genpkey -paramfile dhp.pem -out dhkey.pem
Output DH parameters for safe prime group ffdhe2048:
openssl genpkey -genparam -algorithm DH -out dhp.pem -pkeyopt group:ffdhe2048
Output 2048 bit X9.42 DH parameters with 224 bit subgroup using RFC5114
group2:
openssl genpkey -genparam -algorithm DHX -out dhp.pem -pkeyopt dh_rfc5114:2
Output 2048 bit X9.42 DH parameters with 224 bit subgroup using
FIP186-4 keygen:
openssl genpkey -genparam -algorithm DHX -out dhp.pem -text \
-pkeyopt pbits:2048 -pkeyopt qbits:224 -pkeyopt digest:SHA256 \
-pkeyopt gindex:1 -pkeyopt dh_paramgen_type:2
Output 1024 bit X9.42 DH parameters with 160 bit subgroup using
FIP186-2 keygen:
openssl genpkey -genparam -algorithm DHX -out dhp.pem -text \
-pkeyopt pbits:1024 -pkeyopt qbits:160 -pkeyopt digest:SHA1 \
-pkeyopt gindex:1 -pkeyopt dh_paramgen_type:1
Output 2048 bit DH parameters:
openssl genpkey -genparam -algorithm DH -out dhp.pem \
-pkeyopt dh_paramgen_prime_len:2048
Output 2048 bit DH parameters using a generator:
openssl genpkey -genparam -algorithm DH -out dhpx.pem \
-pkeyopt dh_paramgen_prime_len:2048 \
-pkeyopt dh_paramgen_type:1
Generate EC parameters:
openssl genpkey -genparam -algorithm EC -out ecp.pem \
-pkeyopt ec_paramgen_curve:secp384r1 \
-pkeyopt ec_param_enc:named_curve
Generate EC key from parameters:
openssl genpkey -paramfile ecp.pem -out eckey.pem
Generate EC key directly:
openssl genpkey -algorithm EC -out eckey.pem \
-pkeyopt ec_paramgen_curve:P-384 \
-pkeyopt ec_param_enc:named_curve
Generate an X25519 private key:
openssl genpkey -algorithm X25519 -out xkey.pem
Generate an ED448 private key:
openssl genpkey -algorithm ED448 -out xkey.pem
HISTORY
The ability to use NIST curve names, and to generate an EC key
directly, were added in OpenSSL 1.0.2. The ability to generate X25519
keys was added in OpenSSL 1.1.0. The ability to generate X448, ED25519
and ED448 keys was added in OpenSSL 1.1.1.
The -engine option was deprecated in OpenSSL 3.0.
COPYRIGHT
Copyright 2006-2023 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.
3.0.13 2025-09-18 OPENSSL-GENPKEY(1SSL)
Generated by dwww version 1.16 on Tue Dec 16 15:02:36 CET 2025.