This takes a plain ssh_hashalg, and constructs the most natural kind
of HMAC wrapper around it, taking its key length and output length
to be the hash's output length. In other words, it converts SHA-foo
into exactly the thing usually called HMAC-SHA-foo.
It does it by constructing a new ssh2_macalg vtable, and including it
in the same memory allocation as the actual hash object. That's the
first time in PuTTY I've done it this way.
Nothing yet uses this, but a new piece of code is about to.
I saw a post on comp.security.ssh just now where someone had
encountered an SSH server that would _only_ speak that, which makes it
worth bothering to implement.
The totally obvious implementation works, and passes the test cases
from RFC 6234.
(cherry picked from commit b77e985513)
This provides a convenient hook to be called between SSH messages, for
the crypto components to do any per-message processing like
incrementing a sequence number.
marshal.h now provides a macro put_fmt() which allows you to write
arbitrary printf-formatted data to an arbitrary BinarySink.
We already had this facility for strbufs in particular, in the form of
strbuf_catf(). That was able to take advantage of knowing the inner
structure of a strbuf to minimise memory allocation (it would snprintf
directly into the strbuf's existing buffer if possible). For a general
black-box BinarySink we can't do that, so instead we dupvprintf into a
temporary buffer.
For consistency, I've removed strbuf_catf, and converted all uses of
it into the new put_fmt - and I've also added an extra vtable method
in the BinarySink API, so that put_fmt can still use strbuf_catf's
more efficient memory management when talking to a strbuf, and fall
back to the simpler strategy when that's not available.
Similarly to 'utils', I've moved all the stuff in the crypto
build-time library into a source directory of its own, and while I'm
at it, split up the monolithic sshauxcrypt.c into its various
unrelated parts.
This is also an opportunity to remove the annoying 'ssh' prefix from
the front of the file names, and give several of them less cryptic
names.
