SSH encryption - SSH

This is a discussion on SSH encryption - SSH ; -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Does the session encryption key ever change in an SSH tunnel? - -- To reply by email remove "_nospam" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.0 (MingW32) iEYEARECAAYFAkPOa5sACgkQzIf+rZpn0oRu1QCfYE4JtQPEg3 8ZD1hp9knl1U9g bz8AmgMsOgLSl3oej5VfBB3kIBqHvAGo =KC3w -----END PGP SIGNATURE-----...

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Thread: SSH encryption

  1. SSH encryption

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    Does the session encryption key ever change in an SSH tunnel?
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  2. Re: SSH encryption

    On 2006-01-18, Chuck wrote:
    > Does the session encryption key ever change in an SSH tunnel?


    It can, if either the server or client request rekeying (and both support
    it). For OpenSSH that's ssh(1)'s RekeyLimit which is conspicuously absent
    from the man page in current versions. If it were there it would read
    something like:

    RekeyLimit
    Specifies how much data may be transmitted before the session key
    has to be re-negotiated. The argument must be the number of
    bytes, with an optional postfix of ``K'' ``M'' ``G'' to indicate
    Kilo/Mega/Gigabytes. The default is between ``1G'' and ``4G'' ,
    depending on the Cipher. Note that this option applies to proto-
    col version 2 only.

    --
    Darren Tucker (dtucker at zip.com.au)
    GPG key 8FF4FA69 / D9A3 86E9 7EEE AF4B B2D4 37C9 C982 80C7 8FF4 FA69
    Good judgement comes with experience. Unfortunately, the experience
    usually comes from bad judgement.

  3. Re: SSH encryption


    >>>>> "Chuck" == Chuck writes:


    Chuck> Does the session encryption key ever change in an SSH tunnel?

    From the definition of the SSH transport protocol:
    (http://www.snailbook.com/docs/transport.txt)

    ------------------------------------------------------------------------
    9. Key Re-Exchange

    Key re-exchange is started by sending an SSH_MSG_KEXINIT packet when
    not already doing a key exchange (as described in Section 7.1). When
    this message is received, a party MUST respond with its own
    SSH_MSG_KEXINIT message except when the received SSH_MSG_KEXINIT
    already was a reply. Either party MAY initiate the re-exchange, but
    roles MUST NOT be changed (i.e., the server remains the server, and
    the client remains the client).

    Key re-exchange is performed using whatever encryption was in effect
    when the exchange was started. Encryption, compression, and MAC
    methods are not changed before a new SSH_MSG_NEWKEYS is sent after
    the key exchange (as in the initial key exchange). Re-exchange is
    processed identically to the initial key exchange, except for the
    session identifier that will remain unchanged. It is permissible to
    change some or all of the algorithms during the re-exchange. Host
    keys can also change. All keys and initialization vectors are
    recomputed after the exchange. Compression and encryption contexts
    are reset.

    It is recommended that the keys are changed after each gigabyte of
    transmitted data or after each hour of connection time, whichever
    comes sooner. However, since the re-exchange is a public key
    operation, it requires a fair amount of processing power and should
    not be performed too often.
    ------------------------------------------------------------------------

    Whether this is actually done is an implementation issue. Most SSH
    software today supports rekeying, including OpenSSH, Tectia, PuTTY, and
    VShell.

    --
    Richard Silverman
    res@qoxp.net


  4. Re: SSH encryption

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    Thanks Darren and Richard.

    Next question. If SSH runs over SSL, doesn't SSL have some sort of
    encryption key renegotiation built in?
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  5. Re: SSH encryption

    In article <%3Pzf.9484$8r1.278@trndny01>,
    Chuck wrote:
    >If SSH runs over SSL,


    It doesn't.

    --
    Ben Harris

  6. Re: SSH encryption

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    Ben Harris wrote:
    > In article <%3Pzf.9484$8r1.278@trndny01>,
    > Chuck wrote:
    >> If SSH runs over SSL,

    >
    > It doesn't.
    >


    Then why does OpenSSH depend on OpenSSL. Is it using functions provided
    by OpenSSL, but not SSL itself?

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  7. Re: SSH encryption

    On Thu, 19 Jan 2006 17:41:27 +0000, Chuck wrote:

    > -----BEGIN PGP SIGNED MESSAGE-----
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    >
    > Ben Harris wrote:
    >> In article <%3Pzf.9484$8r1.278@trndny01>, Chuck
    >> wrote:
    >>> If SSH runs over SSL,

    >>
    >> It doesn't.
    >>
    >>

    > Then why does OpenSSH depend on OpenSSL. Is it using functions provided by
    > OpenSSL, but not SSL itself?


    It just uses the crypto support in OpenSSL, not the SSL protocol support.



  8. Re: SSH encryption

    OpenSSH delivers the data to be transmitted to the encryption
    functions in OpenSSL, but does not use the SSL protocol. It uses
    its own implementation of the SSH protocol.

    Thomas Carter wrote:
    > On Thu, 19 Jan 2006 17:41:27 +0000, Chuck wrote:
    >
    >> -----BEGIN PGP SIGNED MESSAGE-----
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    >>
    >> Ben Harris wrote:
    >>> In article <%3Pzf.9484$8r1.278@trndny01>, Chuck
    >>> wrote:
    >>>> If SSH runs over SSL,
    >>> It doesn't.
    >>>
    >>>

    >> Then why does OpenSSH depend on OpenSSL. Is it using functions provided by
    >> OpenSSL, but not SSL itself?

    >
    > It just uses the crypto support in OpenSSL, not the SSL protocol support.
    >
    >


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