DES

[Xenitellis S]

	-----Original Message-----
	From:	Kissandrakis S. Gewrgios
[SMTP:kissand at rea.edu.physics.uoc.gr]
	Sent:	Friday, December 10, 1999 1:53 PM
	To:	linux-greek-users at tux.hellug.gr
	Subject:	DES



	Exw thn entypwsh oti to DES 64bit encryption einia gia olo ton kosmo
O DES dexete kleidia 64 bit, ostoso o xristis xrisimopoiei ta 56. Ta
"password" einai 7-bit ASCII
kai 8eorite oti to ogdoo exei ti morfi a8roismatos elegxou. Giafto to logo,
o DES anaferete san
algori8mos me kleidi mege8ous 56-bit.
	kai to DES 128bit enscyption mono gia USA (pou apagoreuetai h
exagwgh tou)
O DES mporei na xrisimopoiei8ei me tin morfi EDE (EncryptDecryptEncrypt),
diladi
pairneis 3 kleidia, kryptografeis me to proto, apokryptografeis me to
deftero kai kryptografeis me to trito,
me afti ti seira.
(H "apokryptografisi" na min se merdevei, me epilegmena la8os kleidi, i
apokryptografisi exei ti morfi
kyprografisis, dioti to apotelesma den exei kamia sxesi me to arxiko
minima).
Stin periptosi ayti, o algori8mos onomazete 3DES (Triple DES). To mege8os
kleidiou einai 3*56=168bits.

Mia paralagi tou 3DES einai me dio kleidia. Einai opos to parapanw, alla to
proto kai to trito kleidi einai idia.
Opote to synoliko mege8os kleidiou einai 112bits.
O logos pou xrisimopoioune tin ekdosi ayti, einai gia symbatotita me tin
yparxousa egkatistimeni vasi,
kyrios sto trapeziko xoro. Otan 8elei kapoios exei kapoio password
kryptografimeno me aplo DES kai 8elei
na ay8entikopoii8ei (elegxos au8entikotitas), to programma metavainei stin
katastasi symbatotitas kai 
kanei xrisi tou idiou kwdikou gia to proto miso tou kleidiou kai to deftero
miso (apotelesma single DES).

Perissotera sto http://www.rsasecurity.com/rsalabs/faq/
<http://www.rsasecurity.com/rsalabs/faq/> 
Oson afora tin politiki ejagogis apo tis HPA, apagorevetai na egax8ei o
3DES, se opoia morfi.
Ejaireseis yparxoun gia xrisi sto trapeziko xoro. Me to Wassenar (sp?)
agreement, ta pragmata ginontai
pio refsta...

Simos Xenitellis
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