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Improve privacy: use const tweak + try for const filter parameters

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This commit is contained in:
Matt Corallo 2013-01-17 18:15:51 -05:00
parent 1ea4cb457d
commit 5f070e9861
1 changed files with 10 additions and 3 deletions
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13
core/src/main/java/com/google/bitcoin/core/PeerGroup.java
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@ -137,6 +137,9 @@ public class PeerGroup extends AbstractIdleService {
public static final double DEFAULT_BLOOM_FILTER_FP_RATE = 0.0005;
// The false positive rate for bloomFilter
private double bloomFilterFPRate = DEFAULT_BLOOM_FILTER_FP_RATE;
// We use a constant tweak to avoid giving up privacy when we regenerate our filter with new keys
private final long bloomFilterTweak = new Random().nextLong();
private int lastBloomFilterElementCount;
/**
* Creates a PeerGroup with the given parameters. No chain is provided so this node will report its chain height
@ -561,10 +564,14 @@ public class PeerGroup extends AbstractIdleService {
}
if (chain == null || !chain.shouldVerifyTransactions()) {
long nTweak = new Random().nextLong();
BloomFilter filter = new BloomFilter(elements, bloomFilterFPRate, nTweak);
// We stair-step our element count so that we avoid creating a filter with different parameters
// as much as possible as that results in a loss of privacy.
// The constant 100 here is somewhat arbitrary, but makes sense for small to medium wallets -
// it will likely mean we never need to create a filter with different parameters.
lastBloomFilterElementCount = elements > lastBloomFilterElementCount ? elements + 100 : lastBloomFilterElementCount;
BloomFilter filter = new BloomFilter(lastBloomFilterElementCount, bloomFilterFPRate, bloomFilterTweak);
for (Wallet w : wallets)
filter.merge(w.getBloomFilter(elements, bloomFilterFPRate, nTweak));
filter.merge(w.getBloomFilter(elements, bloomFilterFPRate, bloomFilterTweak));
bloomFilter = filter;
log.info("Sending all peers an updated Bloom Filter.");
for (Peer peer : peers)