genrsa - generate an RSA private key
] [ -out filename
] [ -aes128
] [ -aes192
] [ -aes256
] [ -aria192
] [ -aria256
] [ -camellia128
] [ -camellia256
] [ -des
] [ -des3
] [ -f4
] [ -3
] [ -rand file(s)
] [ -engine
] [ numbits
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
- 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
- -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.
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
Because key generation is a random process the time taken to generate a key may
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