GENRSA(1) OpenSSL GENRSA(1)NAMEgenrsa - generate an RSA private key
openssl genrsa [-out filename] [-passout arg] [-des] [-des3] [-idea]
[-f4] [-3] [-randfile(s)] [-engine id] [numbits]
The genrsa command generates an RSA private key.
the output filename. If this argument is not specified then
standard output is used.
the output file password source. For more information about the
format of arg see the PASS PHRASE ARGUMENTS section in openssl(1).
These options encrypt 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 a pass phrase is prompted for if it is not supplied via the
the public exponent to use, either 65537 or 3. The default is
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 a OS-dependent character. The
separator is ; for MS-Windows, , for OpenVMS, and : for all others.
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 512.
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 size).
Because key generation is a random process the time taken to generate a
key may vary somewhat.
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 ALSOgendsa(1)1.0.1g 2014-03-17 GENRSA(1)