# phpman > man > openssl-genrsa(1) > **TLDR:** Generate RSA private keys. > - Generate an RSA private key of 2048 bits to `stdout`: `openssl genrsa` - Save an RSA private key of an arbitrary number of bits to the output file: `openssl genrsa -out {{output_file.key}} {{1234}}` - Generate an RSA private key and encrypt it with AES256 (you will be prompted for a passphrase): `openssl genrsa {{aes256}}` *Source: tldr-pages* --- [OPENSSL-GENRSA(1SSL)](https://www.chedong.com/phpMan.php/man/OPENSSL-GENRSA/1SSL/markdown) OpenSSL [OPENSSL-GENRSA(1SSL)](https://www.chedong.com/phpMan.php/man/OPENSSL-GENRSA/1SSL/markdown) ## NAME openssl-genrsa - generate an RSA private key ## SYNOPSIS **openssl** **genrsa** [**-help**] [**-out** _filename_] [**-passout** _arg_] [**-aes128**] [**-aes192**] [**-aes256**] [**-aria128**] [**-aria192**] [**-aria256**] [**-camellia128**] [**-camellia192**] [**-camellia256**] [**-des**] [**-des3**] [**-idea**] [**-F4**] [**-f4**] [**-3**] [**-primes** _num_] [**-verbose**] [**-traditional**] [**-rand** _files_] [**-writerand** _file_] [**-engine** _id_] [**-provider** _name_] [**-provider-path** _path_] [**-propquery** _propq_] [**numbits**] ## DESCRIPTION This command has been deprecated. The [**openssl-genpkey**(1)](https://www.chedong.com/phpMan.php/man/openssl-genpkey/1/markdown) command should be used instead. This command generates an RSA private key. ## OPTIONS ### -help Print out a usage message. ### -out Output the key to the specified file. If this argument is not specified then standard output is used. ### -passout The output file password source. For more information about the format see [**openssl-passphrase-options**(1)](https://www.chedong.com/phpMan.php/man/openssl-passphrase-options/1/markdown). ### -aes128 -aes192 -aes256 -aria128 -aria192 -aria256 -camellia128 -camellia192 ### -camellia256 -des -des3 -idea 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. ### -F4 -f4 -3 The public exponent to use, either 65537 or 3. The default is 65537. The **-3** option has been deprecated. ### -primes Specify the number of primes to use while generating the RSA key. The _num_ parameter must be a positive integer that is greater than 1 and less than 16. If _num_ is greater than 2, then the generated key is called a 'multi-prime' RSA key, which is defined in RFC 8017. ### -verbose Print extra details about the operations being performed. ### -traditional Write the key using the traditional PKCS#1 format instead of the PKCS#8 format. ### -rand -writerand See "Random State Options" in [**openssl**(1)](https://www.chedong.com/phpMan.php/man/openssl/1/markdown) for details. ### -engine See "Engine Options" in [**openssl**(1)](https://www.chedong.com/phpMan.php/man/openssl/1/markdown). This option is deprecated. ### -provider ### -provider-path ### -propquery See "Provider Options" in [**openssl**(1)](https://www.chedong.com/phpMan.php/man/openssl/1/markdown), [**provider**(7)](https://www.chedong.com/phpMan.php/man/provider/7/markdown), and [**property**(7)](https://www.chedong.com/phpMan.php/man/property/7/markdown). ### numbits The size of the private key to generate in bits. This must be the last option specified. The default is 2048 and values less than 512 are not allowed. ## NOTES RSA private key generation essentially involves the generation of two or more 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, ***** means the current prime starts a regenerating progress due to some failed tests. 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. But in general, more primes lead to less generation time of a key. ## SEE ALSO [**openssl**(1)](https://www.chedong.com/phpMan.php/man/openssl/1/markdown), [**openssl-genpkey**(1)](https://www.chedong.com/phpMan.php/man/openssl-genpkey/1/markdown), [**openssl-gendsa**(1)](https://www.chedong.com/phpMan.php/man/openssl-gendsa/1/markdown) ## HISTORY This command was deprecated in OpenSSL 3.0. ## COPYRIGHT Copyright 2000-2021 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 <>. 3.0.2 2026-06-02 [OPENSSL-GENRSA(1SSL)](https://www.chedong.com/phpMan.php/man/OPENSSL-GENRSA/1SSL/markdown)