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- Unix, Linux Command
genrsa - generate an RSA private key
The genrsa command generates an RSA private key.
the output filename. If this argument is not specified then standard output is
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 -passout 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)).
Multiple files can be specified separated by a OS-dependent character.
The separator is ; for MS-Windows, , for OpenVMS, and : for
specifying an engine (by its unique id string) will cause req
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).