GENPKEY(1)

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