mirror of
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cc9d920c78
It now expects its standard input to be connected to the same PuTTY its standard output is talking to, i.e. expects to be invoked as a proxy command. It conducts the same sample key exchange as it used to, but now reads the SSH greeting and first couple of packets back from PuTTY and minimally checks that they're something like what it was expecting. (In the process, I've also fixed a mistake in the Python message code enumeration, which caused one of those expect() calls to fail.)
93 lines
4.8 KiB
Python
Executable File
93 lines
4.8 KiB
Python
Executable File
#!/usr/bin/env python
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# Example Python script to synthesise the server end of an SSH key exchange.
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# This script expects to be run with its standard input and output
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# channels both connected to PuTTY. Run it by means of a command such
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# as
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#
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# rm -f test.log && ./plink -sshrawlog test.log -v -proxycmd './contrib/samplekex.py' dummy
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#
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# It will conduct the whole of an SSH connection setup, up to the
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# point where it ought to present a valid host key signature and
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# switch over to the encrypted protocol; but because this is a simple
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# script (and also because at that point PuTTY would annoyingly give a
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# host key prompt), it doesn't actually bother to do either, and will
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# instead present a nonsense signature and terminate. The above sample
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# command will log the whole of the exchange from PuTTY's point of
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# view in 'test.log'.
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#
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# The intention is that this forms example code that can be easily
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# adapted to demonstrate bugs in our SSH connection setup. With more
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# effort it could be expanded into some kind of a regression-testing
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# suite, although in order to reliably test particular corner cases
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# that would probably also need PuTTY-side modifications to make the
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# random numbers deterministic.
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import sys, random
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from encodelib import *
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# A random Diffie-Hellman group, taken from an SSH server I made a
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# test connection to.
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groupgen = 5
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group = 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# An RSA key, generated specially for this script.
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rsaexp = 0x10001
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rsamod = 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# 16 bytes of random data for the start of KEXINIT.
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cookie = "".join([chr(random.randint(0,255)) for i in range(16)])
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def expect(var, expr):
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expected_val = eval(expr)
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if var != expected_val:
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sys.stderr.write("Expected %s (%s), got %s\n" % (
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expr, repr(expected_val), repr(var)))
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sys.exit(1)
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sys.stdout.write(greeting("SSH-2.0-Example KEX synthesis"))
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greeting = sys.stdin.readline()
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expect(greeting[:8], '"SSH-2.0-"')
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sys.stdout.write(
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clearpkt(SSH2_MSG_KEXINIT,
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cookie,
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name_list(("diffie-hellman-group-exchange-sha256",)), # kex
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name_list(("ssh-rsa",)), # host keys
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name_list(("aes128-ctr",)), # client->server ciphers
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name_list(("aes128-ctr",)), # server->client ciphers
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name_list(("hmac-sha2-256",)), # client->server MACs
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name_list(("hmac-sha2-256",)), # server->client MACs
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name_list(("none",)), # client->server compression
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name_list(("none",)), # server->client compression
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name_list(()), # client->server languages
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name_list(()), # server->client languages
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boolean(False), # first kex packet does not follow
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uint32(0)))
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sys.stdout.flush()
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intype, inpkt = read_clearpkt(sys.stdin)
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expect(intype, "SSH2_MSG_KEXINIT")
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intype, inpkt = read_clearpkt(sys.stdin)
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expect(intype, "SSH2_MSG_KEX_DH_GEX_REQUEST")
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expect(inpkt, "uint32(0x400) + uint32(0x400) + uint32(0x2000)")
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sys.stdout.write(
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clearpkt(SSH2_MSG_KEX_DH_GEX_GROUP,
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mpint(group),
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mpint(groupgen)))
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sys.stdout.flush()
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intype, inpkt = read_clearpkt(sys.stdin)
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expect(intype, "SSH2_MSG_KEX_DH_GEX_INIT")
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sys.stdout.write(
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clearpkt(SSH2_MSG_KEX_DH_GEX_REPLY,
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ssh_rsa_key_blob(rsaexp, rsamod),
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mpint(random.randint(2, group-2)),
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ssh_rsa_signature_blob(random.randint(2, rsamod-2))))
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sys.stdout.flush()
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