[VPN] How to calculate Key Length in DES and 3DES?

[Siddhartha Jain]

DES uses 64-bit key out of which 8 bits are for parity
effectively giving you 56-bits. 3DES is DES done three
times (either in Encrypt-Decrypt-Encrypt mode or
Encrypt-Encrypt-Encrypt mode). Each step uses a 56-bit
key giving you 56x3 = 168 bits. But you really can't
call it a 168-bit key.

>From http://www.acmet.com/html/3des.html

Let EK (I) and DK(I) represent the DES encryption and
decryption of I using DES key K respectively. Each
TDEA encryption/decryption operation is a compound
operation of DES encryption and decryption operations.
The following operations are used:

TDEA encryption operation: the transformation of a
64-bit block I into a 64-bit block O that is defined
as follows:
 O = EK3(DK2(EK1(I))).

TDEA decryption operation: the transformation of a
64-bit block I into a 64-bit block O that is defined
as follows: 
O = DK1(EK2(DK3(I)))

I am not sure what you mean by --- "But I want to know
how many characters we can use in both and also how to
calculate the length of the characters."

A character usually is a byte long i.e. 8 bits.

Siddhartha


--- Sandeep Dhadwal <dhadwal_sandeepsingh at hotmail.com>
wrote: > Hi All,
> 
> I would like to what is the key length in DES and 3
> DES.  I know that DES 
> supports 56 bit and 3DES 168 bit keys.  But I want
> to know how many 
> characters we can use in both and also how to
> calculate the length of the 
> characters.
> 
> Regards,
> Sandeep Singh Dhadwal
> 
> 
> 
> 
> 
> 
>
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