genpkey.1ssl man page

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.

-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).


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.


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.


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


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.

Dsa Parameter Generation Options


The number of bits in the generated parameters. If not specified 1024 is used.

DH Parameter Generation Options


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.

Ec Parameter Generation Options

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".

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 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.  Signature
  B          1.2.643.  Signature
  C          1.2.643.  Signature
  XA         1.2.643.  Key exchange
  XB         1.2.643.  Key exchange
  test       1.2.643.  Test purposes

X25519 Key Generation Options

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.

Referenced By

openssl.1ssl(1), pkey.1ssl(1), pkeyparam.1ssl(1), pkeyutl.1ssl(1).

2018-03-27 1.1.0h OpenSSL