# 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 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)

## COPYRIGHT
       Copyright 2000-2023 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 <<https://www.openssl.org/source/license.html>>.

3.0.13                                       2026-07-29                         [_OPENSSL-GENRSA_(1SSL)](https://www.chedong.com/phpMan.php/man/OPENSSL-GENRSA/1SSL/markdown)