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Viaccess Algorithme Infos

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lol Viaccess Algorithme Infos

مُساهمة من طرف starsat الأحد 10 أغسطس 2008, 8:08 am

Here some info about the Viaccess algorithm :

Viaccess is a modification of Eurocrypt M. In this mod the key has 8 bytes then EC-M has only 7.
If the 8th byte is zero then Viaccess works exactly like EC-M.

If the 8th byte is nonzero then this will trigger several different small mods. One of these mods is in DES routine. 7 key bytes are used in des but the 8th byte is used in special core function in every DES round. This mod is done just before expansion E and it alters the 5th data byte which is the first of the right-hand 4 data bytes to be used in the DES-round.
Therefore it has affect in S-boxes 1,2,3 and 8. The mod is done only with this byte for expansion E and the original byte remains the same.

In this mod the 8th key byte is multiplied with the data byte for at get a 16 bit word. Then the data byte is added to this word (upper 8 bit byte is incremented if there was a carry with the lower byte). Then the 8th key
byte is added to the word on the same way. Then the upper byte is subtracted from the lower byte. If there was a carry in this subtract then result is incremented by 1. Then this result byte is used instead of the original byte in expansion E.

All hash algorithms are working like in EC-M when this DES modification is done.
CA 88 and CA 18 message processing :
If the 8th keybyte is nonzero then first 7 keybytes are rotated left by 2 bytes.
This means key(k1 k2 k3 k4 k5 k6 k7 k8) -> key(k3 k4 k5 k6 k7 k1 k2 k8)
If the 8th key byte is even then this is the last modification but if it is add then there is still one very complicated data modification.
First there is one constant which is 5Ah if the 8th key byte is odd and less than 10h. If the 8th byte is odd and bigger than 10h then this constant is A5h.
In the data modification is used hash result for the 8 bytes which are just before the encrypted data. If there are not enough bytes in these hash results then values 00 are used in missing bytes. These hash bytes are first ANDed with the constant and then XORed with the encrypted data bytes. Result bytes are then used as input data for DES. Ofcourse DES is done with necessary mods.
After DES the result bytes are ready for CA C0 message or other use in CA 18 messages
starsat
starsat
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Directeur Adjoint-نائب مدير

عدد الرسائل : 107
تاريخ التسجيل : 20/07/2008

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lol رد: Viaccess Algorithme Infos

مُساهمة من طرف محمد احمد عبده الأحد 31 أغسطس 2008, 4:16 am

thanks cheers

محمد احمد عبده

عدد الرسائل : 2
تاريخ التسجيل : 22/04/2008

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lol رد: Viaccess Algorithme Infos

مُساهمة من طرف satpctv الأحد 31 أغسطس 2008, 5:59 pm

merci bcoup^s
satpctv
satpctv

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تاريخ التسجيل : 04/01/2008

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lol رد: Viaccess Algorithme Infos

مُساهمة من طرف mead-amine الإثنين 23 مايو 2011, 4:37 am

Merci

mead-amine

عدد الرسائل : 1
تاريخ التسجيل : 23/05/2011

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