Re: DES and 3DES

From: flip (flip_alpha_at_safebunch.com)
Date: 10/24/04

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    Date: Sun, 24 Oct 2004 10:37:19 -0700

    "Subba Rao" <castellan2004-mail@SPAMBUSTER.yahoo.com> wrote in message
    news:e9adnTekHYbzUebcRVn-rg@adelphia.com...
    > Hello everyone,
    >
    > I have a question about DES and 3DES.
    >
    > This is what I know so far.
    >
    > • Initially DES was developed by IBM and used the Lucifier algorithm
    > (128-bit). It was modified to use 64-bit (56 bit key and 8 bit parity
    > bit) key and was called Data Encryption Algorithm (DEA).
    >
    > • 3DES (same as DES) performs 48 rounds (as opposed to 16 rounds of DES)
    > of encryption.
    >
    > What is the default DES or 3DES key length? Is it 56 bit or 128 bit?
    > I am under the impression that 3DES always uses 128 bit encryption.
    > It is for that reason alone it is more secure. Am I right on that?
    >
    > Can 3DES encryption be done with smaller key sizes? If yes, is it
    > part of the best practices?
    >
    > For encryption/decryption, does 3DES perform 48 rounds on the
    > data OR use 3 separate 56-bit keys on the data?
    >
    > Thank you in advance.
    >
    > --
    > SR
    > castellan2004-mail@SPAMBUSTER.yahoo.com
    > Please remove SPAMBUSTER to reply via email.

    This is a better question for sci.crypt.

    Anyway, DES became a NIST standard and was recently revoked since it can be
    broken by doing an exhaustive key search.

    The key size is 56-bits (don't worry about the 8 parity bits).

    3-DES uses encrypt-decrypt-encrypt (EDE) or encrypt-encrypt-encrypt with
    either 2 keys or three keys (called 2-key 3DES or 3-key 3DES).

    Neither has been broken and likely will not be.

    3DES gets you 112- bits of security.

    DES and 3DES are being replaced with the Advanced Encryption Standard (AES)
    and you can find the FIPs (spec) on the NIST web site.

    It gives 128, 192 or 256-bits for a key size and all the same modes of
    operation (including new ones) are available.

    You didn't say what you were doing with the cipher, but I'd recommend using
    AES or any of the other four AES finalists.

    There is a TON of information on DES and 3DES via google.

    HTH

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