Provided by: openssl_1.0.2g-1ubuntu4.20_amd64 
NAME
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.
-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.
-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 below for more details.
-genparam
generate a set of parameters instead of a private key. If used this option must precede and
-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 1024 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.
DSA PARAMETER GENERATION OPTIONS
dsa_paramgen_bits:numbits
The number of bits in the generated parameters. If not specified 1024 is used.
DH PARAMETER GENERATION OPTIONS
dh_paramgen_prime_len:numbits
The number of bits in the prime parameter p.
dh_paramgen_generator:value
The value to use for the generator g.
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.
EC PARAMETER GENERATION OPTIONS
ec_paramgen_curve:curve
the EC curve to use.
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
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 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