openssl-genpkey (1)

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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.

-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 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.

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

The parameter generation options below can also be supplied as key generation options. This can (for example) generate a key from a named curve without the need to use an explicit parameter file.

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''.

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 .gost file in the engines/ccgost directory of the source distribution for more details.

Use of a parameter file for the

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

X25519 KEY GENERATION OPTIONS

The X25519 algorithm does not currently support any key generation options.

NOTES

The use of the genpkey program is encouraged over the algorithm specific utilities because additional algorithm options and provided algorithms can be used.

EXAMPLES

Generate an private key using default parameters:

 openssl genpkey -algorithm RSA -out key.pem

Encrypt output private key using 128 bit

and the passphrase ``hello'':

 openssl genpkey -algorithm RSA -out key.pem -aes-128-cbc -pass pass:hello

Generate a 2048 bit

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

parameters:

 openssl genpkey -genparam -algorithm DSA -out dsap.pem \
                                                -pkeyopt dsa_paramgen_bits:1024

Generate

key from parameters:

 openssl genpkey -paramfile dsap.pem -out dsakey.pem

Generate 1024 bit

parameters:

 openssl genpkey -genparam -algorithm DH -out dhp.pem \
                                        -pkeyopt dh_paramgen_prime_len:1024

Output

bit parameters with 224 bit subgroup:

 openssl genpkey -genparam -algorithm DH -out dhp.pem -pkeyopt dh_rfc5114:2

Generate

key from parameters:

 openssl genpkey -paramfile dhp.pem -out dhkey.pem

Generate

parameters:

 openssl genpkey -genparam -algorithm EC -out ecp.pem \
        -pkeyopt ec_paramgen_curve:secp384r1 \
        -pkeyopt ec_param_enc:named_curve

Generate

key from parameters:

 openssl genpkey -paramfile ecp.pem -out eckey.pem

Generate

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

HISTORY

The ability to use curve names, and to generate an key directly, were added in OpenSSL 1.0.2.

COPYRIGHT

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

in the source distribution or at <www.openssl.org/source/license.html>.