Provided by: openssl_1.1.1-1ubuntu2_amd64

**NAME**

openssl-genrsa, genrsa - generate an RSA private key

**SYNOPSIS**

opensslgenrsa[-help] [-outfilename] [-passoutarg] [-aes128] [-aes192] [-aes256] [-aria128] [-aria192] [-aria256] [-camellia128] [-camellia192] [-camellia256] [-des] [-des3] [-idea] [-f4] [-3] [-randfile...] [-writerandfile] [-engineid] [-primesnum] [numbits]

**DESCRIPTION**

Thegenrsacommand generates an RSA private key.

**OPTIONS**

-helpPrint out a usage message.-outfilenameOutput the key to the specified file. If this argument is not specified then standard output is used.-passoutargThe output file password source. For more information about the format ofargsee thePASSPHRASEARGUMENTSsection inopenssl(1).-aes128,-aes192,-aes256,-aria128,-aria192,-aria256,-camellia128,-camellia192,-camellia256,-des,-des3,-ideaThese 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-passoutargument.-F4|-3The public exponent to use, either 65537 or 3. The default is 65537.-randfile...A file or files containing random data used to seed the random number generator. Multiple files can be specified separated by an OS-dependent character. The separator is;for MS-Windows,,for OpenVMS, and:for all others. [-writerandfile] Writes random data to the specifiedfileupon exit. This can be used with a subsequent-randflag.-engineidSpecifying an engine (by its uniqueidstring) will causegenrsato 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.-primesnumSpecify the number of primes to use while generating the RSA key. Thenumparameter must be a positive integer that is greater than 1 and less than 16. Ifnumis greater than 2, then the generated key is called a 'multi-prime' RSA key, which is defined in RFC 8017.numbitsThe 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**

gendsa(1)

**COPYRIGHT**

Copyright 2000-2018 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 <https://www.openssl.org/source/license.html>.