ask a question about DES

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2 total messages Started by Jason Sun, 21 Feb 1999 00:00

Author: Jason
Date: Sun, 21 Feb 1999 00:00

18 lines
1623 bytes

HELLO.....
I read the writing "How to implment the DES"
There is a point that Ican understand....
"process the key
get a 64-bit key from the user(every 8th bit is considered a parity bit.
For a key to have correct parity,each byte should contain an odd number
of "1" bits.)"
I don't understand how DES can differentiate "ff"&"7f" when discared the
parity bit?
After discared parity bit,ff=1111111(in binary) 7f=1111111....right?

Please show me where is the different?Thank you

                                                                   JASON



Scorpio

Re: ask a question about DES

Author: Richard Outerbridge
Date: Sun, 21 Feb 1999 00:00

31 lines
1946 bytes

-----BEGIN PGP SIGNED MESSAGE-----

1999-02-21 13:05:28 EDT
Responding to article <7ap9c1$eb7$1@news.seed.net.tw>, by "Jason"
<jason008@ms1.seeder.net> :

DES keys ignore every eighth bit of each byte.  The unused bit may
be used for odd parity detection.  Unhelpfully, the bit that ends up
being ignored is the >least< significant one in normal representation.
For example, the two following 64-bit hex strings are equivalent DES
keys.  Only the first one will pass odd-parity checks.

Key1: 0123 4567 89ab cdef
Key2: 0022 4466 88aa ccee

outer

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-- 
"Just an eccentric soul with a curiosity for the bizarre."
PGPpubkey 1024/0EEAAF21 1994/07/23 <outer@interlog.com>
Fingerprint = 6A89 D49F D3DA 12E4  040A 273B F383 0127

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