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Make minimum quorum Byzantine fault tolerant (RIPD-1461)
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@wilsonianb
wilsonianb committed Apr 25, 2017
1 parent 84816d1 commit 6ef1f30
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Showing 3 changed files with 61 additions and 47 deletions.
46 changes: 23 additions & 23 deletions src/ripple/app/misc/ValidatorList.h
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Original file line number Diff line number Diff line change
Expand Up @@ -309,7 +309,8 @@ class ValidatorList
std::function<void(PublicKey const&, bool)> func) const;

static std::size_t
calculateQuorum (std::size_t nTrustedKeys);
calculateMinimumQuorum (
std::size_t nListedKeys, bool unlistedLocal=false);

private:
/** Check response for trusted valid published list
Expand Down Expand Up @@ -399,36 +400,35 @@ ValidatorList::onConsensusStart (
}
}

// This quorum guarantees sufficient overlap with the trusted sets of other
// nodes using the same set of published lists.
std::size_t quorum = keyListings_.size()/2 + 1;

// Increment the quorum to prevent two unlisted validators using the same
// even number of listed validators from forking.
if (localPubKey_.size() && ! localKeyListed &&
rankedKeys.size () > 1 && keyListings_.size () % 2 != 0)
++quorum;
// This minimum quorum of 2f + 1 guarantees safe overlap with the trusted
// sets of other nodes using the same set of published lists.
// Safety is guaranteed with up to 1/3 listed validators being malicious.
std::size_t quorum = calculateMinimumQuorum (keyListings_.size(),
localPubKey_.size() && !localKeyListed);

JLOG (j_.debug()) <<
rankedKeys.size() << " of " << keyListings_.size() <<
" listed validators eligible for inclusion in the trusted set";

auto size = rankedKeys.size();

// Use all eligible keys if there is less than 10 listed validators or
// only one trusted list
if (size < 10 || publisherLists_.size() == 1)
{
// Try to raise the quorum toward or above 80% of the trusted set
std::size_t const targetQuorum = ValidatorList::calculateQuorum (size);
if (targetQuorum > quorum)
quorum = targetQuorum;
}
else
// Do not require 80% quorum for less than 10 trusted validators
if (size >= 10)
{
// reduce the trusted set size so that the quorum represents
// at least 80%
size = quorum * 1.25;
// Use all eligible keys if there is only one trusted list
if (publisherLists_.size() == 1)
{
// Try to raise the quorum to at least 80% of the trusted set
std::size_t const targetQuorum = size - size / 5;
if (targetQuorum > quorum)
quorum = targetQuorum;
}
else
{
// Reduce the trusted set size so that the quorum represents
// at least 80%
size = quorum * 1.25;
}
}

if (minimumQuorum_ && (seenValidators.empty() ||
Expand Down
20 changes: 14 additions & 6 deletions src/ripple/app/misc/impl/ValidatorList.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -409,15 +409,23 @@ ValidatorList::for_each_listed (
}

std::size_t
ValidatorList::calculateQuorum (std::size_t nTrustedKeys)
ValidatorList::calculateMinimumQuorum (
std::size_t nListedKeys, bool unlistedLocal)
{
// Use 80% for large values of n, but have special cases for small numbers.
constexpr std::array<std::size_t, 10> quorum{{ 0, 1, 2, 2, 3, 3, 4, 5, 6, 7 }};
// Use 2f + 1 for large values of n, but have special cases for small numbers.
constexpr std::array<std::size_t, 6> quorum{{ 0, 1, 2, 2, 3, 3 }};

if (nTrustedKeys < quorum.size())
return quorum[nTrustedKeys];

return nTrustedKeys - nTrustedKeys / 5;
// The number of listed validators is increased to preserve the safety
// guarantee for two unlisted validators using the same set of listed
// validators.
if (unlistedLocal && nListedKeys >= quorum.size())
++nListedKeys;

if (nListedKeys < quorum.size())
return quorum[nListedKeys];

return nListedKeys * 2/3 + 1;
}

} // ripple
42 changes: 24 additions & 18 deletions src/test/app/ValidatorList_test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -125,17 +125,26 @@ class ValidatorList_test : public beast::unit_test::suite
}

void
testCalculateQuorum ()
testCalculateMinimumQuorum ()
{
testcase ("Calculate Quorum");
testcase ("Calculate Minimum Quorum");

for(std::size_t i = 1; i < 20; ++i)
{
auto const quorum = ValidatorList::calculateQuorum(i);
if (i < 10)
auto const quorum = ValidatorList::calculateMinimumQuorum(i);
if (i <= 5)
{
BEAST_EXPECT(quorum >= (i/2 + 1));
BEAST_EXPECT(ValidatorList::calculateMinimumQuorum(
i, true /* untrusted local validator */) == quorum);
}
else
BEAST_EXPECT(quorum == std::ceil (i * 0.8));
{
BEAST_EXPECT(quorum == std::floor (i * 2/3) + 1);
BEAST_EXPECT(ValidatorList::calculateMinimumQuorum(
i, true /* untrusted local validator */) ==
ValidatorList::calculateMinimumQuorum(i + 1));
}
}
}

Expand Down Expand Up @@ -522,7 +531,7 @@ class ValidatorList_test : public beast::unit_test::suite
// onConsensusStart should make all available configured
// validators trusted
trustedKeys->onConsensusStart (activeValidators);
BEAST_EXPECT(trustedKeys->quorum () == 12);
BEAST_EXPECT(trustedKeys->quorum () == 14);
std::size_t i = 0;
for (auto const& val : cfgKeys)
{
Expand Down Expand Up @@ -571,7 +580,7 @@ class ValidatorList_test : public beast::unit_test::suite
manifests.applyManifest(std::move (*m1)) ==
ManifestDisposition::accepted);
trustedKeys->onConsensusStart (activeValidators);
BEAST_EXPECT(trustedKeys->quorum () == 13);
BEAST_EXPECT(trustedKeys->quorum () == 15);
BEAST_EXPECT(trustedKeys->listed (masterPublic));
BEAST_EXPECT(trustedKeys->trusted (masterPublic));
BEAST_EXPECT(trustedKeys->listed (signingPublic1));
Expand All @@ -584,12 +593,11 @@ class ValidatorList_test : public beast::unit_test::suite
auto m2 = Manifest::make_Manifest (makeManifestString (
masterPublic, masterPrivate,
signingPublic2, signingKeys2.second, 2));

BEAST_EXPECT(
manifests.applyManifest(std::move (*m2)) ==
ManifestDisposition::accepted);
trustedKeys->onConsensusStart (activeValidators);
BEAST_EXPECT(trustedKeys->quorum () == 13);
BEAST_EXPECT(trustedKeys->quorum () == 15);
BEAST_EXPECT(trustedKeys->listed (masterPublic));
BEAST_EXPECT(trustedKeys->trusted (masterPublic));
BEAST_EXPECT(trustedKeys->listed (signingPublic2));
Expand All @@ -613,7 +621,7 @@ class ValidatorList_test : public beast::unit_test::suite
BEAST_EXPECT(manifests.getSigningKey (masterPublic) == masterPublic);
BEAST_EXPECT(manifests.revoked (masterPublic));
trustedKeys->onConsensusStart (activeValidators);
BEAST_EXPECT(trustedKeys->quorum () == 12);
BEAST_EXPECT(trustedKeys->quorum () == 15);
BEAST_EXPECT(trustedKeys->listed (masterPublic));
BEAST_EXPECT(!trustedKeys->trusted (masterPublic));
BEAST_EXPECT(!trustedKeys->listed (signingPublicMax));
Expand Down Expand Up @@ -700,7 +708,7 @@ class ValidatorList_test : public beast::unit_test::suite
localKey, cfgKeys, cfgPublishers));

trustedKeys->onConsensusStart (activeValidators);
BEAST_EXPECT(trustedKeys->quorum () == 3);
BEAST_EXPECT(trustedKeys->quorum () == 2);

// local validator key is always trusted
BEAST_EXPECT(trustedKeys->trusted (localKey));
Expand Down Expand Up @@ -770,7 +778,7 @@ class ValidatorList_test : public beast::unit_test::suite
emptyLocalKey, cfgKeys, cfgPublishers));
trustedKeys->onConsensusStart (activeValidators);
BEAST_EXPECT(trustedKeys->quorum () ==
ValidatorList::calculateQuorum(cfgKeys.size()));
ValidatorList::calculateMinimumQuorum(cfgKeys.size()));
for (auto const& key : activeValidators)
BEAST_EXPECT(trustedKeys->trusted (key));
}
Expand Down Expand Up @@ -799,11 +807,9 @@ class ValidatorList_test : public beast::unit_test::suite
localKey, cfgKeys, cfgPublishers));
trustedKeys->onConsensusStart (activeValidators);

// When running as an unlisted validator,
// the quorum is incremented by 1 for 3 or 5 trusted validators.
auto expectedQuorum = ValidatorList::calculateQuorum(cfgKeys.size());
if (cfgKeys.size() == 3 || cfgKeys.size() == 5)
++expectedQuorum;
auto expectedQuorum = ValidatorList::calculateMinimumQuorum(
cfgKeys.size(), true /* unlisted local validator */);

BEAST_EXPECT(trustedKeys->quorum () == expectedQuorum);
for (auto const& key : activeValidators)
BEAST_EXPECT(trustedKeys->trusted (key));
Expand All @@ -816,7 +822,7 @@ class ValidatorList_test : public beast::unit_test::suite
run() override
{
testGenesisQuorum ();
testCalculateQuorum ();
testCalculateMinimumQuorum ();
testConfigLoad ();
testApplyList ();
testUpdate ();
Expand Down

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