openssh now disables RSA/SHA-1 by default, so using RSA/SHA-1 will
eventually cause us problems:
https://undeadly.org/cgi?action=article;sid=20210830113413
in addition, github will disable RSA/SHA-1 for recently added RSA keys:
https://github.blog/2021-09-01-improving-git-protocol-security-github/
this patch modifies ssh.c to use RSA/SHA-256 (aka rsa-sha2-256)
instead of RSA/SHA-1 (aka ssh-rsa) as the public key algorithm.
NOTE: public rsa keys and thumbprints are ***NOT AFFECTED***
by this patch.
while we're here, remove the workaround for github.com. it seems
that github has fixed their implementation, and does not look into
macalgs when we're using an aead cipher.
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When resizing windows, vt would signal ssh by updating
the window size and sending an interrupt. Ssh reacted
by forwarding both the winch and an interrupt.
This change adds a WINCH generation counter so that
ssh can differentiate between resizes and interrupts.
If an interrupt comes in, and the WINCH generation
changes, then the interrupt is taken as signalling a
WINCH.
As checking for all zero has to be done in a timing-safe
way to avoid a side channel, it is best todo this here
instead of letting the caller deal with it.
This adds a return type of int to curve25519_dh_finish()
where returning 0 means we got a all zero shared key.
RFC7748 states:
The check for the all-zero value results from the fact
that the X25519 function produces that value if it
operates on an input corresponding to a point with small
order, where the order divides the cofactor of the curve.
key exchange with git@github.com fails as they appear to try to
negotiate a mac algorithm even tho we use an AEAD cipher which
does not use a mac algorithm.
the work around is to supply a dummy mac algorithm that they
can negotiate to make them happy.
in mux mode, ssh relays raw MSG_CHANNEL_*
messages on standard input and output while
still handling authentication and key exchange
internally.
the intend is to use the mux mode to implement
something like the old sshnet ontop of ssh.
respond to MSG_GLOBAL_REQUEST with MSG_REQUEST_FAILURE
as stated by rfc4254 when server wants a reply.
failing todo so breaks some proprietary keep-alive schemes.
initThumbprints() now takes an application tag argument
so x509 and ssh can coexist.
the thumbprint entries can now hold both sha1 and sha256
hashes. okThumbprint() now takes a len argument for the
hash length used.
the new function okCertificate() hashes the certificate
with both and checks for any matches.
on failure, okCertificate() returns 0 and sets error string.
we also check for include loops now in thumbfiles, limiting
the number of includes to 8.
when we initiate re-key exchange we data packets can still
come in. so instead we have everything that can come in all
the time in dispatch() function (including KEXINIT) and have
the receiver process just call that in a loop. exclude dispatch
and the sender proc from corrupting each others sendpkt() calls
with the QLock sl.
