=pod

=head1 NAME

openssl-genrsa,
genrsa - generate an RSA private key

=head1 SYNOPSIS

B<openssl> B<genrsa>
[B<-help>]
[B<-out filename>]
[B<-passout arg>]
[B<-aes128>]
[B<-aes192>]
[B<-aes256>]
[B<-aria128>]
[B<-aria192>]
[B<-aria256>]
[B<-camellia128>]
[B<-camellia192>]
[B<-camellia256>]
[B<-des>]
[B<-des3>]
[B<-idea>]
[B<-f4>]
[B<-3>]
[B<-rand file...>]
[B<-writerand file>]
[B<-engine id>]
[B<-primes num>]
[B<numbits>]

=head1 DESCRIPTION

The B<genrsa> command generates an RSA private key.

=head1 OPTIONS

=over 4

=item B<-help>

Print out a usage message.

=item B<-out filename>

Output the key to the specified file. If this argument is not specified then
standard output is used.

=item B<-passout arg>

The output file password source. For more information about the format
of B<arg> see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.

=item B<-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 B<-passout> argument.

=item B<-F4|-3>

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

=item B<-rand file...>

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 B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
all others.

=item [B<-writerand file>]

Writes random data to the specified I<file> upon exit.
This can be used with a subsequent B<-rand> flag.

=item B<-engine id>

Specifying an engine (by its unique B<id> string) will cause B<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.

=item B<-primes num>

Specify the number of primes to use while generating the RSA key. The B<num>
parameter must be a positive integer that is greater than 1 and less than 16.
If B<num> is greater than 2, then the generated key is called a 'multi-prime'
RSA key, which is defined in RFC 8017.

=item B<numbits>

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

=back

=head1 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 B<.> represents each number which
has passed an initial sieve test, B<+> means a number has passed a single
round of the Miller-Rabin primality test, B<*> 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.

=head1 BUGS

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).

=head1 SEE ALSO

L<gendsa(1)>

=head1 COPYRIGHT

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
L<https://www.openssl.org/source/license.html>.

=cut