genrsa - generate an RSA private key
[-out filename] [-passout arg] [-des] [-des3] [-idea] [-f4] [-3] [-rand file(s)] [-engine id] [numbits]
The genrsa command generates an RSA private key.
- -out filename
the output filename. If this argument is not specified then standard output
- -passout arg
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.
- -rand file(s)
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.
- -engine id
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).
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