Re: 3DES key-length for data authentication

Date: 12/09/02

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    To: Rick Moen <>
    Date: Mon, 9 Dec 2002 01:12:10 -0600

    On 5 Dec 2002,, you wrote:

    > Quoting Hari-Isoft (
    > > I would like to know the key-length used for 3DES data encryption in
    > > openssh. I thought that it should be 192 (3 * 64) bits, but the sshd
    > > man page states 128 bit key used for 3DES.
    > An old set of notes I have says single DES starts out with 64-bit keys,
    > but it's 56-bit when you account for the parity bit. Thus the raw
    > key-length of 3DES is 56 * 3 = 168 bit. The _effective_ length as
    > implemented (3DES-CBC algorithm?) may be less: Maybe one of the real
    > crypto people will comment.

    The effective keylength of Triple-DES is 112 bits. I don't recall the
    rationale for this now - it should be available in all the usual
    places; e.g. google, "triple-DES effective keylength".

    Jay Moore
    (not a _real_ crypto person)