genpkey
GENPKEY(1SSL) OpenSSL GENPKEY(1SSL)
NAME
openssl-genpkey, genpkey - generate a private key
SYNOPSIS
openssl genpkey [-help] [-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
-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
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,
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
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 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.
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".
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.
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:
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 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.
COPYRIGHT
Copyright 2006-2019 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (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>.
1.1.1f 2023-10-10 GENPKEY(1SSL)
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