NAME

       genrsa - generate an RSA private key

SYNOPSIS

       openssl genrsa [-out filename] [-passout arg] [-des] [-des3] [-idea] [-f4] [-3] [-rand
       file(s)] [-engine id] [numbits]

DESCRIPTION

       The genrsa command generates an RSA private key.

OPTIONS

       -out filename
           the output filename. If this argument is not specified then standard output is used.

       -passout arg
           the output file password source. For more information about the format of arg see the
           PASS PHRASE ARGUMENTS section in openssl(1).

       -des|-des3|-idea
           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.

       -F4|-3
           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.

       numbits
           the size of the private key to generate in bits. This must be the last option
           specified. The default is 512.

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 . 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.

BUGS

       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

       gendsa(1)