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genpkey - generate a private key


openssl genpkey [-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.


-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).

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 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.

Print an (unencrypted) text representation of private and public keys and parameters
along with the PEM or DER structure.


The options supported by each algorith and indeed each implementation of an algorithm can
vary. The options for the OpenSSL implementations are detailed below.


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.


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


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.


the EC curve to use.


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.

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


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

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