=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<-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>, B<-aes192>, B<-aes256>, B<-camellia128>, B<-camellia192>, B<-camellia256>, B<-des>, B<-des3>, B<-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 and values less than 512 are not allowed.

=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 SEE ALSO

L<gendsa(1)>

=head1 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
L<https://www.openssl.org/source/license.html>.

=cut