genrsa(1ssl)genrsa(1ssl)NAMEgenrsa - Generate an RSA private key
SYNOPSIS
openssl genrsa [-out filename] [-passout arg] [-des] [-des3] [-idea]
[-f4] [-3] [-randfilename] [numbits]
OPTIONS
Outputs the filename. If this argument is not specified then standard
output is used. Outputs the file password source. For more information
about the format of arg see the Pass Phrase Arguments section in
openssl(1ssl). Encrypts the private key with the DES, triple DES, or
the IDEA ciphers, respectively, before outputting it. If none of these
options is specified no encryption is used. If encryption is used,
there is a prompt for a pass phrase if it is not supplied via the -pas‐
sout argument. The public exponent to use, either 65537 or 3. The
default is 65537. A file or files containing random data used to seed
the random number generator, or an EGD socket. (See RAND_egd(3).) Mul‐
tiple files can be specified separated by an OS-dependent character.
The separator is a semicolon (;) for MS-Windows, a comma (,) for Open‐
VMS, and a colon (:) for all others. The size of the private key to
generate in bits. This must be the last option specified. The default
is 512.
DESCRIPTION
The genrsa command generates an RSA private key.
NOTES
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 period (.) repre‐
sents each number that passed an initial sieve test. A plus sign (+)
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 size.
Because key generation is a random process, the time taken to generate
a key may vary.
RESTRICTIONS
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).
SEE ALSO
Commands: gendsa(1ssl)genrsa(1ssl)