Go to main content

man pages section 1: User Commands

Exit Print View

Updated: Wednesday, February 9, 2022

genrsa (1openssl)


genrsa - generate an RSA private key


openssl genrsa [-help] [-out filename] [-passout arg] [-aes128]
[-aes192] [-aes256] [-aria128] [-aria192] [-aria256] [-camellia128]
[-camellia192] [-camellia256] [-des] [-des3] [-idea] [-f4] [-3] [-rand
file(s)] [-engine id] [numbits]


GENRSA(1openssl)                    OpenSSL                   GENRSA(1openssl)

       openssl-genrsa, genrsa - generate an RSA private key

       openssl genrsa [-help] [-out filename] [-passout arg] [-aes128]
       [-aes192] [-aes256] [-aria128] [-aria192] [-aria256] [-camellia128]
       [-camellia192] [-camellia256] [-des] [-des3] [-idea] [-f4] [-3] [-rand
       file(s)] [-engine id] [numbits]

       The genrsa command generates an RSA 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.

       -passout arg
           the output file password source. For more information about the
           format of arg see the PASS PHRASE ARGUMENTS section in openssl(1).

           These options encrypt the private key with specified cipher before
           outputting it. If none of these options is specified no encryption
           is used. If encryption is used a pass phrase is prompted for if it
           is not supplied via the -passout argument.

           the public exponent to use, either 65537 or 3. The default is

       -rand file(s)
           a file or files containing random data used to seed the random
           number generator, or an EGD socket (see RAND_egd(3)).  Multiple
           files can be specified separated by an OS-dependent character.  The
           separator is ; for MS-Windows, , for OpenVMS, and : for all others.

       -engine id
           specifying an engine (by its unique id string) will cause genrsa 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.

           the size of the private key to generate in bits. This must be the
           last option specified. The default is 2048.

       See attributes(7) for descriptions of the following attributes:

       |Availability   | library/security/openssl |
       |Stability      | Pass-through uncommitted |

       RSA private key generation essentially involves the generation of two
       prime numbers. When generating a private key various symbols will be
       output to indicate the progress of the generation. A . represents each
       number which has passed an initial sieve test, + means a number has
       passed a single round of the Miller-Rabin primality test. A newline
       means that the number has passed all the prime tests (the actual number
       depends on the key size).

       Because key generation is a random process the time taken to generate a
       key may vary somewhat.

       Source code for open source software components in Oracle Solaris can
       be found at https://www.oracle.com/downloads/opensource/solaris-source-

       This software was built from source available at
       https://github.com/oracle/solaris-userland.  The original community
       source was downloaded from

       Further information about this software can be found on the open source
       community website at https://www.openssl.org/.

       A quirk of the prime generation algorithm is that it cannot generate
       small primes. Therefore the number of bits should not be less that 64.
       For typical private keys this will not matter because for security
       reasons they will be much larger (typically 1024 bits).


       Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the OpenSSL license (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

1.0.2za                           2021-08-24                  GENRSA(1openssl)