Ubuntu Manpage: openssl-genpkey - generate a private key

Provided by: openssl_3.0.13-0ubuntu3.5_amd64

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.

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                                             2025-02-05                              OPENSSL-GENPKEY(1SSL)