12-04-2008
dd - binary file
I have a task that says: make a file (called binaryfile ) that contains
4 bytes of NULL data
6 bytes of random data
8 bytes of 1
10 bytes of 5
and 12 bytes of 9.
For the first 2, I can used :
dd if=/dev/null of=binaryfile bs=8 count =4 and
dd if=/dev/urandom of=binaryfile bs=8 count=6 seek=4, but how can I do the rest ???
I know, bs will remain 8 (8 bits) and seek will increase after each append to my file. My question is, how to tell dd what bits to copy (other than 0 or random).
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LEARN ABOUT DEBIAN
ipsec_ranbits
IPSEC_RANBITS(8) [FIXME: manual] IPSEC_RANBITS(8)
NAME
ipsec_ranbits - generate random bits in ASCII form
SYNOPSIS
ipsec ranbits [--quick] [--continuous] [--bytes] nbits
DESCRIPTION
Ranbits obtains nbits (rounded up to the nearest byte) high-quality random bits from random(4), and emits them on standard output as an
ASCII string. The default output format is datatot(3) h format: lowercase hexadecimal with a 0x prefix and an underscore every 32 bits.
The --quick option produces quick-and-dirty random bits: instead of using the high-quality random bits from /dev/random, which may take
some time to supply the necessary bits if nbits is large, ranbits uses /dev/urandom, which yields prompt results but lower-quality
randomness.
The --continuous option uses datatot(3) x output format, like h but without the underscores.
The --bytes option causes nbits to be interpreted as a byte count rather than a bit count.
FILES
/dev/random, /dev/urandom
SEE ALSO
ipsec_datatot(3), random(4)
HISTORY
Written for the Linux FreeS/WAN project <http://www.freeswan.org> by Henry Spencer.
BUGS
There is an internal limit on nbits, currently 20000.
Without --quick, ranbits's run time is difficult to predict. A request for a large number of bits, at a time when the system's entropy pool
is low on randomness, may take quite a while to satisfy.
Though not a bug of ranbits, the direct use of /dev/hw_random, the Linux hardware random number generator is not supported because it can
produce very non-random data. To properly use /dev/hw_random, the rngd daemon should be used to read from /dev/hw_random and write to
/dev/random, while performing a FIPS test on the hardware random read. No changes to Openswan are required for this support - just a
running rngd.
[FIXME: source] 10/06/2010 IPSEC_RANBITS(8)