encrypt with TripleDES, decrypt with DES, doesnt work ?

Discussion in 'ASP .Net Security' started by Lech Migdal, Apr 7, 2004.

  1. Lech Migdal

    Lech Migdal Guest

    Hi

    I have such a problem - I've tried to encrypt a file with TripleDES and then
    decrypt it with DES, but failed.
    AFAIK, TripleDES uses 3x DES (EEE), so decrypting it with DES should be
    possible.

    I've tested DES and it is ok (encrypts and decrypts file without problem).
    The passwords provided
    and IV are the same. (for the TripleDES I give 24 bytes of password, to DES
    I give password bytes 1 to 8, 9 to 18 and 19 to 27)

    So maybe TripleDES is doing something with the password that I am not aware
    of ?

    thanks in advance
    LM
    Lech Migdal, Apr 7, 2004
    #1
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  2. In fact the process is not that simple as to pass three times with DES using
    the key splitted in three parts. These two algorithms are block ciphers and
    basically they process the data in blocks of a fixed size at a time. The
    3DES algorithm process each block 3 times, each of them with a different
    part of the 24 bytes key (3 x 8). When you decrypt with DES, you are
    processing all the cipher data with each key part, so this way you are not
    getting the same output as 3DES because you are not processing each block at
    a time.

    Regards,
    Hernan.

    --
    Hernan de Lahitte
    Lagash Systems S.A.
    http://weblogs.asp.net/hernandl
    Shadowfax Dev Team

    This posting is provided "AS IS" with no warranties, and confers no rights.

    "Lech Migdal" <> wrote in message
    news:c50npe$k5i$...
    > Hi
    >
    > I have such a problem - I've tried to encrypt a file with TripleDES and

    then
    > decrypt it with DES, but failed.
    > AFAIK, TripleDES uses 3x DES (EEE), so decrypting it with DES should be
    > possible.
    >
    > I've tested DES and it is ok (encrypts and decrypts file without problem).
    > The passwords provided
    > and IV are the same. (for the TripleDES I give 24 bytes of password, to

    DES
    > I give password bytes 1 to 8, 9 to 18 and 19 to 27)
    >
    > So maybe TripleDES is doing something with the password that I am not

    aware
    > of ?
    >
    > thanks in advance
    > LM
    >
    >
    >
    Hernan de Lahitte, Apr 7, 2004
    #2
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