MCOOKIE

mcookie − generate magic cookies for xauth

mcookie [−v] [−f filename ]

mcookie generates a 128-bit random hexadecimal number for use with the X authority system. Typical usage:

xauth add :0 . ‘mcookie‘

The "random" number generated is actually the output of the MD5 message digest fed with various piece of random information: the current time, the process id, the parent process id, the contents of an input file (if −f is specified), and several bytes of information from the first of the following devices which is present: /dev/random, /dev/urandom, files in /proc, /dev/audio.

The entropy in the generated 128-bit is probably quite small (and, therefore, vulnerable to attack) unless a non-pseudorandom number generator is used (e.g., /dev/random under Linux).

It is assumed that none of the devices opened will block.

/dev/random
/dev/urandom
/dev/audio
/proc/stat
/proc/loadavg

X(1), xauth(1), md5sum(1)