man > openssl-genpkey(1)

OPENSSL-GENPKEY(1SSL)                          OpenSSL                         OPENSSL-GENPKEY(1SSL)

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.

       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.  This  is
           only used by "fips186_4" and "fips186_2" key generation.

       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.  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                                       2026-07-29                        OPENSSL-GENPKEY(1SSL)