SSHv1's exponent is always 35 - SSH

This is a discussion on SSHv1's exponent is always 35 - SSH ; Every time I connect to an SSHv1 server and get the public key modulo / exponent, the exponent is always 35. Should it be? The SSHv1 spec states that the public (and server) exponent should be transmited as an mpint. ...

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Thread: SSHv1's exponent is always 35

  1. SSHv1's exponent is always 35

    Every time I connect to an SSHv1 server and get the public key modulo /
    exponent, the exponent is always 35. Should it be?

    The SSHv1 spec states that the public (and server) exponent should be
    transmited as an mpint. Why bother transmiting it at all if it's
    always going to be 35? Or why not transmit it as a regular 32-bit
    integer as opposed to an mpint?


  2. Re: SSHv1's exponent is always 35

    yawnmoth wrote:
    > Every time I connect to an SSHv1 server and get the public key modulo /
    > exponent, the exponent is always 35. Should it be?


    It's not _guaranteed_ to be. One particular key generator always
    chooses the exponent to be 35, and that particular key generator is
    more widely used than others, so you will see an overwhelming
    majority of exponents being 35. But it's permitted for someone to
    write a key generator which uses a different (or even - *gasp* - a
    randomly chosen) exponent, and therefore clients and servers are
    required to be able to handle this case correctly in case it comes
    up.

    (PuTTY's key generator consistently uses 37, as it happens, because
    my generation algorithm found it more convenient to have the
    exponent be prime. However, PuTTY's key generator isn't often used
    to generate _server_ public keys, although it should work fine if
    someone really wanted to.)
    --
    Simon Tatham "A defensive weapon is one with my finger on the
    trigger. An offensive weapon is one with yours."

  3. Re: SSHv1's exponent is always 35


    Simon Tatham wrote:
    > yawnmoth wrote:
    >
    >
    > One particular key generator always
    > chooses the exponent to be 35, and that particular key generator is
    > more widely used than others, so you will see an overwhelming
    > majority of exponents being 35.

    This particular keygen would be OpenSSH's?


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