openssl-genpkey, genpkey - generate a private key
openssl genpkey [-help] [-out filename] [-outform PEM|DER] [-pass arg] [-cipher] [-engine id] [-paramfile file] [-algorithm alg] [-pkeyopt opt:value] [-genparam] [-text]
The genpkey command generates a private key.
Print out a usage message.
Output the key to the specified file. If this argument is not specified then standard output is used.
This specifies the output format DER or PEM.
The options supported by each algorithm and indeed each implementation of an algorithm can vary. The options for the OpenSSL implementations are detailed below.
The number of bits in the generated key. If not specified 1024 is used.
The RSA public exponent value. This can be a large decimal or hexadecimal value if preceded by 0x. Default value is 65537.
The number of bits in the generated parameters. If not specified 1024 is used.
The number of bits in the prime parameter p.
The value to use for the generator g.
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.
The EC parameter generation options below can also be supplied as EC key generation options. This can (for example) generate a key from a named curve without the need to use an explicit parameter file.
the EC curve to use. OpenSSL supports NIST curve names such as "P-256".
the encoding to use for parameters. The "encoding" parameter must be either "named_curve" or "explicit".
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 directory 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.
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
The X25519 algorithm does not currently support any key generation options.
The use of the genpkey program is encouraged over the algorithm specific utilities because additional algorithm options and ENGINE provided algorithms can be used.
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 1024 bit DSA parameters:
openssl genpkey -genparam -algorithm DSA -out dsap.pem \
-pkeyopt dsa_paramgen_bits:1024
Generate DSA key from parameters:
openssl genpkey -paramfile dsap.pem -out dsakey.pem
Generate 1024 bit DH parameters:
openssl genpkey -genparam -algorithm DH -out dhp.pem \
-pkeyopt dh_paramgen_prime_len:1024
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
The ability to use NIST curve names, and to generate an EC key directly, were added in OpenSSL 1.0.2.
Copyright 2006-2016 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.