bad bignum encoding for curve25519-sha256 at

Bryan Drewery bdrewery at
Thu Apr 24 11:03:43 EST 2014

On 4/20/2014 2:14 AM, Damien Miller wrote:
> Hi,
> So I screwed up when writing the support for the curve25519 KEX method
> that doesn't depend on OpenSSL's BIGNUM type - a bug in my code left
> leading zero bytes where they should have been skipped. The impact of
> this is that OpenSSH 6.5 and 6.6 will fail during key exchange with a
> peer that implements curve25519-sha256 at properly about 0.2%
> of the time (one in every 512ish connections).
> We've fixed this for OpenSSH 6.7 by avoiding the curve25519-sha256
> key exchange for previous versions, but I'd recommend distributors
> of OpenSSH apply this patch so the affected code doesn't become
> too entrenched in LTS releases.
> The patch fixes the bug and makes OpenSSH identify itself as 6.6.1 so as
> to distinguish itself from the incorrect versions so the compatibility
> code to disable the affected KEX isn't activated.
> I've committed this on the 6.6 branch too.
> Apologies for the hassle.
> -d

Am I the only one who finds a bugfix non-release via unsigned mail with
an inline patch a problem?

Bryan Drewery

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