crypto(3) ?

Torbjorn Tornkvist <>
Fri Mar 12 23:19:28 CET 2004


Thanx a lot Peter !
(I just got encrypted passwords with esmb to work.)

Cheers, Tobbe



 wrote:

>Hi,  
>
>It is covered, but you have to use a special case of the des_cbc_encrypt/3
>function as follows (referring to the example in your letter below):
>
>  E(Ki,Dj) = crypto:des_cbc_encrypt(Ki, 0, Dj), i=0,Kmax, j=0,..Dmax,
>
>where Ki and Dj are 8 byte quantities (for each Ki only 7 bits are 
>considered).
>
>The des functions in `crypto' are for the Cipher Block Chaining (CBC)
>mode, where results of the previous encryption/decryption step is fed into
>the next step by the initializing vector, IV, but can be used for the 
>basic DES mode as well:
>
>If IV is set to zero (it is xored with the first 8 byte segment of input),
>and 8 byte is provided as input, you get the basic DES
>encryption/decryption of an 8 byte quantity.
>
>This is not at all obvious, but true. FIPS 81 states the details.
>
>/Peter
>
>
>On Thu, 4 Mar 2004, Torbjörn Törnkvist wrote:
>
>  
>
>>Hi,
>>
>>I've been comparing the crypto(3) man page with the CIFS  description
>>on how the (SMB) session key is computed, trying to understand if they
>>are the same. Perhaps someone (Peter ?) could comment on this?
>>
>>The CIFS explanation:
>> ------------------------------------
>>E(K, D) denote the DES block mode encryption function [FIPS 81] , which
>>accepts a seven byte key (K) and an eight byte data block (D) and produces
>>an eight byte encrypted data block as its value.
>>
>>Ex(K,D) denote the extension of DES to longer keys and data blocks. If the
>>data to be encrypted is longer than eight bytes, the encryption function is
>>applied to each block of eight bytes in sequence and the results are 
>>concatenated
>>together. If the key is longer than seven bytes, each 8 byte block of 
>>data is first
>>completely encrypted using the first seven bytes of the key, then the 
>>second seven
>>bytes, etc., appending the results each time. For example, to encrypt 
>>the 16 byte
>>quantity D0D1 with the 14 byte key K0K1,
>>Ex(K0K1,D0D1) = concat(E(K0,D0),E(K0,D1),E(K1,D0),E(K1,D1))
>>
>>So is this algorithm covered by the crypto module?
>>This just gives me headache...
>>
>>Cheers, Tobbe
>>
>>
>>
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>
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