Make addrman's bucket placement deterministic.

Give each address a single fixed location in the new and tried tables,
which become simple fixed-size arrays instead of sets and vectors.

This prevents attackers from having an advantages by inserting an
address multiple times.

This change was suggested as Countermeasure 1 in
Eclipse Attacks on Bitcoin’s Peer-to-Peer Network, Ethan Heilman,
Alison Kendler, Aviv Zohar, Sharon Goldberg. ePrint Archive Report
2015/263. March 2015.

It is also more efficient.

2 files changed, 231 insertions, 206 deletions

diff --git a/src/addrman.cpp b/src/addrman.cpp
index 0c09a24470..8310f0fe70 100644
--- a/src/addrman.cpp
+++ b/src/addrman.cpp
@@ -14,12 +14,12 @@ int CAddrInfo::GetTriedBucket(const uint256& nKey) const
 {
     CDataStream ss1(SER_GETHASH, 0);
     std::vector<unsigned char> vchKey = GetKey();
-    ss1 << ((unsigned char)32) << nKey << vchKey;
+    ss1 << nKey << vchKey;
     uint64_t hash1 = Hash(ss1.begin(), ss1.end()).GetCheapHash();
 
     CDataStream ss2(SER_GETHASH, 0);
     std::vector<unsigned char> vchGroupKey = GetGroup();
-    ss2 << ((unsigned char)32) << nKey << vchGroupKey << (hash1 % ADDRMAN_TRIED_BUCKETS_PER_GROUP);
+    ss2 << nKey << vchGroupKey << (hash1 % ADDRMAN_TRIED_BUCKETS_PER_GROUP);
     uint64_t hash2 = Hash(ss2.begin(), ss2.end()).GetCheapHash();
     return hash2 % ADDRMAN_TRIED_BUCKET_COUNT;
 }
@@ -29,15 +29,24 @@ int CAddrInfo::GetNewBucket(const uint256& nKey, const CNetAddr& src) const
     CDataStream ss1(SER_GETHASH, 0);
     std::vector<unsigned char> vchGroupKey = GetGroup();
     std::vector<unsigned char> vchSourceGroupKey = src.GetGroup();
-    ss1 << ((unsigned char)32) << nKey << vchGroupKey << vchSourceGroupKey;
+    ss1 << nKey << vchGroupKey << vchSourceGroupKey;
     uint64_t hash1 = Hash(ss1.begin(), ss1.end()).GetCheapHash();
 
     CDataStream ss2(SER_GETHASH, 0);
-    ss2 << ((unsigned char)32) << nKey << vchSourceGroupKey << (hash1 % ADDRMAN_NEW_BUCKETS_PER_SOURCE_GROUP);
+    ss2 << nKey << vchSourceGroupKey << (hash1 % ADDRMAN_NEW_BUCKETS_PER_SOURCE_GROUP);
     uint64_t hash2 = Hash(ss2.begin(), ss2.end()).GetCheapHash();
     return hash2 % ADDRMAN_NEW_BUCKET_COUNT;
 }
 
+int CAddrInfo::GetBucketPosition(const uint256 &nKey, bool fNew, int nBucket) const
+{
+    CDataStream ss1(SER_GETHASH, 0);
+    std::vector<unsigned char> vchKey = GetKey();
+    ss1 << nKey << (fNew ? 'N' : 'K') << nBucket << vchKey;
+    uint64_t hash1 = Hash(ss1.begin(), ss1.end()).GetCheapHash();
+    return hash1 % ADDRMAN_BUCKET_SIZE;
+}
+
 bool CAddrInfo::IsTerrible(int64_t nNow) const
 {
     if (nLastTry && nLastTry >= nNow - 60) // never remove things tried in the last minute
@@ -128,85 +137,44 @@ void CAddrMan::SwapRandom(unsigned int nRndPos1, unsigned int nRndPos2)
     vRandom[nRndPos2] = nId1;
 }
 
-int CAddrMan::SelectTried(int nKBucket)
+void CAddrMan::Delete(int nId)
 {
-    std::vector<int>& vTried = vvTried[nKBucket];
-
-    // randomly shuffle the first few elements (using the entire list)
-    // find the least recently tried among them
-    int64_t nOldest = -1;
-    int nOldestPos = -1;
-    for (unsigned int i = 0; i < ADDRMAN_TRIED_ENTRIES_INSPECT_ON_EVICT && i < vTried.size(); i++) {
-        int nPos = GetRandInt(vTried.size() - i) + i;
-        int nTemp = vTried[nPos];
-        vTried[nPos] = vTried[i];
-        vTried[i] = nTemp;
-        assert(nOldest == -1 || mapInfo.count(nTemp) == 1);
-        if (nOldest == -1 || mapInfo[nTemp].nLastSuccess < mapInfo[nOldest].nLastSuccess) {
-            nOldest = nTemp;
-            nOldestPos = nPos;
-        }
-    }
+    assert(mapInfo.count(nId) != 0);
+    CAddrInfo& info = mapInfo[nId];
+    assert(!info.fInTried);
+    assert(info.nRefCount == 0);
 
-    return nOldestPos;
+    SwapRandom(info.nRandomPos, vRandom.size() - 1);
+    vRandom.pop_back();
+    mapAddr.erase(info);
+    mapInfo.erase(nId);
+    nNew--;
 }
 
-int CAddrMan::ShrinkNew(int nUBucket)
+void CAddrMan::ClearNew(int nUBucket, int nUBucketPos)
 {
-    assert(nUBucket >= 0 && (unsigned int)nUBucket < vvNew.size());
-    std::set<int>& vNew = vvNew[nUBucket];
-
-    // first look for deletable items
-    for (std::set<int>::iterator it = vNew.begin(); it != vNew.end(); it++) {
-        assert(mapInfo.count(*it));
-        CAddrInfo& info = mapInfo[*it];
-        if (info.IsTerrible()) {
-            if (--info.nRefCount == 0) {
-                SwapRandom(info.nRandomPos, vRandom.size() - 1);
-                vRandom.pop_back();
-                mapAddr.erase(info);
-                mapInfo.erase(*it);
-                nNew--;
-            }
-            vNew.erase(it);
-            return 0;
-        }
-    }
-
-    // otherwise, select four randomly, and pick the oldest of those to replace
-    int n[4] = {GetRandInt(vNew.size()), GetRandInt(vNew.size()), GetRandInt(vNew.size()), GetRandInt(vNew.size())};
-    int nI = 0;
-    int nOldest = -1;
-    for (std::set<int>::iterator it = vNew.begin(); it != vNew.end(); it++) {
-        if (nI == n[0] || nI == n[1] || nI == n[2] || nI == n[3]) {
-            assert(nOldest == -1 || mapInfo.count(*it) == 1);
-            if (nOldest == -1 || mapInfo[*it].nTime < mapInfo[nOldest].nTime)
-                nOldest = *it;
+    // if there is an entry in the specified bucket, delete it.
+    if (vvNew[nUBucket][nUBucketPos] != -1) {
+        int nIdDelete = vvNew[nUBucket][nUBucketPos];
+        CAddrInfo& infoDelete = mapInfo[nIdDelete];
+        assert(infoDelete.nRefCount > 0);
+        infoDelete.nRefCount--;
+        vvNew[nUBucket][nUBucketPos] = -1;
+        if (infoDelete.nRefCount == 0) {
+            Delete(nIdDelete);
         }
-        nI++;
-    }
-    assert(mapInfo.count(nOldest) == 1);
-    CAddrInfo& info = mapInfo[nOldest];
-    if (--info.nRefCount == 0) {
-        SwapRandom(info.nRandomPos, vRandom.size() - 1);
-        vRandom.pop_back();
-        mapAddr.erase(info);
-        mapInfo.erase(nOldest);
-        nNew--;
     }
-    vNew.erase(nOldest);
-
-    return 1;
 }
 
-void CAddrMan::MakeTried(CAddrInfo& info, int nId, int nOrigin)
+void CAddrMan::MakeTried(CAddrInfo& info, int nId)
 {
-    assert(vvNew[nOrigin].count(nId) == 1);
-
     // remove the entry from all new buckets
-    for (std::vector<std::set<int> >::iterator it = vvNew.begin(); it != vvNew.end(); it++) {
-        if ((*it).erase(nId))
+    for (int bucket = 0; bucket < ADDRMAN_NEW_BUCKET_COUNT; bucket++) {
+        int pos = info.GetBucketPosition(nKey, true, bucket);
+        if (vvNew[bucket][pos] == nId) {
+            vvNew[bucket][pos] = -1;
             info.nRefCount--;
+        }
     }
     nNew--;
 
@@ -214,44 +182,36 @@ void CAddrMan::MakeTried(CAddrInfo& info, int nId, int nOrigin)
 
     // which tried bucket to move the entry to
     int nKBucket = info.GetTriedBucket(nKey);
-    std::vector<int>& vTried = vvTried[nKBucket];
-
-    // first check whether there is place to just add it
-    if (vTried.size() < ADDRMAN_TRIED_BUCKET_SIZE) {
-        vTried.push_back(nId);
-        nTried++;
-        info.fInTried = true;
-        return;
-    }
-
-    // otherwise, find an item to evict
-    int nPos = SelectTried(nKBucket);
-
-    // find which new bucket it belongs to
-    assert(mapInfo.count(vTried[nPos]) == 1);
-    int nUBucket = mapInfo[vTried[nPos]].GetNewBucket(nKey);
-    std::set<int>& vNew = vvNew[nUBucket];
-
-    // remove the to-be-replaced tried entry from the tried set
-    CAddrInfo& infoOld = mapInfo[vTried[nPos]];
-    infoOld.fInTried = false;
-    infoOld.nRefCount = 1;
-    // do not update nTried, as we are going to move something else there immediately
-
-    // check whether there is place in that one,
-    if (vNew.size() < ADDRMAN_NEW_BUCKET_SIZE) {
-        // if so, move it back there
-        vNew.insert(vTried[nPos]);
-    } else {
-        // otherwise, move it to the new bucket nId came from (there is certainly place there)
-        vvNew[nOrigin].insert(vTried[nPos]);
+    int nKBucketPos = info.GetBucketPosition(nKey, false, nKBucket);
+
+    // first make space to add it (the existing tried entry there is moved to new, deleting whatever is there).
+    if (vvTried[nKBucket][nKBucketPos] != -1) {
+        // find an item to evict
+        int nIdEvict = vvTried[nKBucket][nKBucketPos];
+        assert(mapInfo.count(nIdEvict) == 1);
+        CAddrInfo& infoOld = mapInfo[nIdEvict];
+
+        // Remove the to-be-evicted item from the tried set.
+        infoOld.fInTried = false;
+        vvTried[nKBucket][nKBucketPos] = -1;
+        nTried--;
+
+        // find which new bucket it belongs to
+        int nUBucket = infoOld.GetNewBucket(nKey);
+        int nUBucketPos = infoOld.GetBucketPosition(nKey, true, nUBucket);
+        ClearNew(nUBucket, nUBucketPos);
+        assert(vvNew[nUBucket][nUBucketPos] == -1);
+
+        // Enter it into the new set again.
+        infoOld.nRefCount = 1;
+        vvNew[nUBucket][nUBucketPos] = nIdEvict;
+        nNew++;
     }
-    nNew++;
+    assert(vvTried[nKBucket][nKBucketPos] == -1);
 
-    vTried[nPos] = nId;
-    // we just overwrote an entry in vTried; no need to update nTried
+    vvTried[nKBucket][nKBucketPos] = nId;
+    nTried++;
     info.fInTried = true;
-    return;
 }
 
 void CAddrMan::Good_(const CService& addr, int64_t nTime)
@@ -281,12 +241,12 @@ void CAddrMan::Good_(const CService& addr, int64_t nTime)
         return;
 
     // find a bucket it is in now
-    int nRnd = GetRandInt(vvNew.size());
+    int nRnd = GetRandInt(ADDRMAN_NEW_BUCKET_COUNT);
     int nUBucket = -1;
-    for (unsigned int n = 0; n < vvNew.size(); n++) {
-        int nB = (n + nRnd) % vvNew.size();
-        std::set<int>& vNew = vvNew[nB];
-        if (vNew.count(nId)) {
+    for (unsigned int n = 0; n < ADDRMAN_NEW_BUCKET_COUNT; n++) {
+        int nB = (n + nRnd) % ADDRMAN_NEW_BUCKET_COUNT;
+        int nBpos = info.GetBucketPosition(nKey, true, nB);
+        if (vvNew[nB][nBpos] == nId) {
             nUBucket = nB;
             break;
         }
@@ -300,7 +260,7 @@ void CAddrMan::Good_(const CService& addr, int64_t nTime)
     LogPrint("addrman", "Moving %s to tried\n", addr.ToString());
 
     // move nId to the tried tables
-    MakeTried(info, nId, nUBucket);
+    MakeTried(info, nId);
 }
 
 bool CAddrMan::Add_(const CAddress& addr, const CNetAddr& source, int64_t nTimePenalty)
@@ -348,12 +308,25 @@ bool CAddrMan::Add_(const CAddress& addr, const CNetAddr& source, int64_t nTimeP
     }
 
     int nUBucket = pinfo->GetNewBucket(nKey, source);
-    std::set<int>& vNew = vvNew[nUBucket];
-    if (!vNew.count(nId)) {
-        pinfo->nRefCount++;
-        if (vNew.size() == ADDRMAN_NEW_BUCKET_SIZE)
-            ShrinkNew(nUBucket);
-        vvNew[nUBucket].insert(nId);
+    int nUBucketPos = pinfo->GetBucketPosition(nKey, true, nUBucket);
+    if (vvNew[nUBucket][nUBucketPos] != nId) {
+        bool fInsert = vvNew[nUBucket][nUBucketPos] == -1;
+        if (!fInsert) {
+            CAddrInfo& infoExisting = mapInfo[vvNew[nUBucket][nUBucketPos]];
+            if (infoExisting.IsTerrible() || (infoExisting.nRefCount > 1 && pinfo->nRefCount == 0)) {
+                // Overwrite the existing new table entry.
+                fInsert = true;
+            }
+        }
+        if (fInsert) {
+            ClearNew(nUBucket, nUBucketPos);
+            pinfo->nRefCount++;
+            vvNew[nUBucket][nUBucketPos] = nId;
+        } else {
+            if (pinfo->nRefCount == 0) {
+                Delete(nId);
+            }
+        }
     }
     return fNew;
 }
@@ -388,13 +361,13 @@ CAddress CAddrMan::Select_(int nUnkBias)
         // use a tried node
         double fChanceFactor = 1.0;
         while (1) {
-            int nKBucket = GetRandInt(vvTried.size());
-            std::vector<int>& vTried = vvTried[nKBucket];
-            if (vTried.size() == 0)
+            int nKBucket = GetRandInt(ADDRMAN_TRIED_BUCKET_COUNT);
+            int nKBucketPos = GetRandInt(ADDRMAN_BUCKET_SIZE);
+            if (vvTried[nKBucket][nKBucketPos] == -1)
                 continue;
-            int nPos = GetRandInt(vTried.size());
-            assert(mapInfo.count(vTried[nPos]) == 1);
-            CAddrInfo& info = mapInfo[vTried[nPos]];
+            int nId = vvTried[nKBucket][nKBucketPos];
+            assert(mapInfo.count(nId) == 1);
+            CAddrInfo& info = mapInfo[nId];
             if (GetRandInt(1 << 30) < fChanceFactor * info.GetChance() * (1 << 30))
                 return info;
             fChanceFactor *= 1.2;
@@ -403,16 +376,13 @@ CAddress CAddrMan::Select_(int nUnkBias)
         // use a new node
         double fChanceFactor = 1.0;
         while (1) {
-            int nUBucket = GetRandInt(vvNew.size());
-            std::set<int>& vNew = vvNew[nUBucket];
-            if (vNew.size() == 0)
+            int nUBucket = GetRandInt(ADDRMAN_NEW_BUCKET_COUNT);
+            int nUBucketPos = GetRandInt(ADDRMAN_BUCKET_SIZE);
+            if (vvNew[nUBucket][nUBucketPos] == -1)
                 continue;
-            int nPos = GetRandInt(vNew.size());
-            std::set<int>::iterator it = vNew.begin();
-            while (nPos--)
-                it++;
-            assert(mapInfo.count(*it) == 1);
-            CAddrInfo& info = mapInfo[*it];
+            int nId = vvNew[nUBucket][nUBucketPos];
+            assert(mapInfo.count(nId) == 1);
+            CAddrInfo& info = mapInfo[nId];
             if (GetRandInt(1 << 30) < fChanceFactor * info.GetChance() * (1 << 30))
                 return info;
             fChanceFactor *= 1.2;
@@ -460,22 +430,30 @@ int CAddrMan::Check_()
     if (mapNew.size() != nNew)
         return -10;
 
-    for (int n = 0; n < vvTried.size(); n++) {
-        std::vector<int>& vTried = vvTried[n];
-        for (std::vector<int>::iterator it = vTried.begin(); it != vTried.end(); it++) {
-            if (!setTried.count(*it))
-                return -11;
-            setTried.erase(*it);
+    for (int n = 0; n < ADDRMAN_TRIED_BUCKET_COUNT; n++) {
+        for (int i = 0; i < ADDRMAN_BUCKET_SIZE; i++) {
+             if (vvTried[n][i] != -1) {
+                 if (!setTried.count(vvTried[n][i]))
+                     return -11;
+                 if (mapInfo[vvTried[n][i]].GetTriedBucket(nKey) != n)
+                     return -17;
+                 if (mapInfo[vvTried[n][i]].GetBucketPosition(nKey, false, n) != i)
+                     return -18;
+                 setTried.erase(vvTried[n][i]);
+             }
         }
     }
 
-    for (int n = 0; n < vvNew.size(); n++) {
-        std::set<int>& vNew = vvNew[n];
-        for (std::set<int>::iterator it = vNew.begin(); it != vNew.end(); it++) {
-            if (!mapNew.count(*it))
-                return -12;
-            if (--mapNew[*it] == 0)
-                mapNew.erase(*it);
+    for (int n = 0; n < ADDRMAN_NEW_BUCKET_COUNT; n++) {
+        for (int i = 0; i < ADDRMAN_BUCKET_SIZE; i++) {
+            if (vvNew[n][i] != -1) {
+                if (!mapNew.count(vvNew[n][i]))
+                    return -12;
+                if (mapInfo[vvNew[n][i]].GetBucketPosition(nKey, true, n) != i)
+                    return -19;
+                if (--mapNew[vvNew[n][i]] == 0)
+                    mapNew.erase(vvNew[n][i]);
+            }
         }
     }
 
diff --git a/src/addrman.h b/src/addrman.h
index 04c7b32eaf..f7c6318448 100644
--- a/src/addrman.h
+++ b/src/addrman.h
@@ -10,7 +10,6 @@
 #include "random.h"
 #include "sync.h"
 #include "timedata.h"
-#include "uint256.h"
 #include "util.h"
 
 #include <map>
@@ -91,6 +90,9 @@ public:
         return GetNewBucket(nKey, source);
     }
 
+    //! Calculate in which position of a bucket to store this entry.
+    int GetBucketPosition(const uint256 &nKey, bool fNew, int nBucket) const;
+
     //! Determine whether the statistics about this entry are bad enough so that it can just be deleted
     bool IsTerrible(int64_t nNow = GetAdjustedTime()) const;
 
@@ -128,14 +130,11 @@ public:
 //! total number of buckets for tried addresses
 #define ADDRMAN_TRIED_BUCKET_COUNT 64
 
-//! maximum allowed number of entries in buckets for tried addresses
-#define ADDRMAN_TRIED_BUCKET_SIZE 64
-
 //! total number of buckets for new addresses
 #define ADDRMAN_NEW_BUCKET_COUNT 256
 
-//! maximum allowed number of entries in buckets for new addresses
-#define ADDRMAN_NEW_BUCKET_SIZE 64
+//! maximum allowed number of entries in buckets for new and tried addresses
+#define ADDRMAN_BUCKET_SIZE 64
 
 //! over how many buckets entries with tried addresses from a single group (/16 for IPv4) are spread
 #define ADDRMAN_TRIED_BUCKETS_PER_GROUP 4
@@ -146,9 +145,6 @@ public:
 //! in how many buckets for entries with new addresses a single address may occur
 #define ADDRMAN_NEW_BUCKETS_PER_ADDRESS 4
 
-//! how many entries in a bucket with tried addresses are inspected, when selecting one to replace
-#define ADDRMAN_TRIED_ENTRIES_INSPECT_ON_EVICT 4
-
 //! how old addresses can maximally be
 #define ADDRMAN_HORIZON_DAYS 30
 
@@ -195,13 +191,13 @@ private:
     int nTried;
 
     //! list of "tried" buckets
-    std::vector<std::vector<int> > vvTried;
+    int vvTried[ADDRMAN_TRIED_BUCKET_COUNT][ADDRMAN_BUCKET_SIZE];
 
     //! number of (unique) "new" entries
     int nNew;
 
     //! list of "new" buckets
-    std::vector<std::set<int> > vvNew;
+    int vvNew[ADDRMAN_NEW_BUCKET_COUNT][ADDRMAN_BUCKET_SIZE];
 
 protected:
 
@@ -215,17 +211,14 @@ protected:
     //! Swap two elements in vRandom.
     void SwapRandom(unsigned int nRandomPos1, unsigned int nRandomPos2);
 
-    //! Return position in given bucket to replace.
-    int SelectTried(int nKBucket);
+    //! Move an entry from the "new" table(s) to the "tried" table
+    void MakeTried(CAddrInfo& info, int nId);
 
-    //! Remove an element from a "new" bucket.
-    //! This is the only place where actual deletions occur.
-    //! Elements are never deleted while in the "tried" table, only possibly evicted back to the "new" table.
-    int ShrinkNew(int nUBucket);
+    //! Delete an entry. It must not be in tried, and have refcount 0.
+    void Delete(int nId);
 
-    //! Move an entry from the "new" table(s) to the "tried" table
-    //! @pre vvUnkown[nOrigin].count(nId) != 0
-    void MakeTried(CAddrInfo& info, int nId, int nOrigin);
+    //! Clear a position in a "new" table. This is the only place where entries are actually deleted.
+    void ClearNew(int nUBucket, int nUBucketPos);
 
     //! Mark an entry "good", possibly moving it from "new" to "tried".
     void Good_(const CService &addr, int64_t nTime);
@@ -254,17 +247,21 @@ protected:
 public:
     /**
      * serialized format:
-     * * version byte (currently 0)
-     * * nKey
+     * * version byte (currently 1)
+     * * 0x20 + nKey (serialized as if it were a vector, for backward compatibility)
      * * nNew
      * * nTried
-     * * number of "new" buckets
+     * * number of "new" buckets XOR 2**30
      * * all nNew addrinfos in vvNew
      * * all nTried addrinfos in vvTried
      * * for each bucket:
      *   * number of elements
      *   * for each element: index
      *
+     * 2**30 is xorred with the number of buckets to make addrman deserializer v0 detect it
+     * as incompatible. This is necessary because it did not check the version number on
+     * deserialization.
+     *
      * Notice that vvTried, mapAddr and vVector are never encoded explicitly;
      * they are instead reconstructed from the other information.
      *
@@ -276,49 +273,53 @@ public:
      *
      * We don't use ADD_SERIALIZE_METHODS since the serialization and deserialization code has
      * very little in common.
-     *
      */
     template<typename Stream>
     void Serialize(Stream &s, int nType, int nVersionDummy) const
     {
         LOCK(cs);
 
-        unsigned char nVersion = 0;
+        unsigned char nVersion = 1;
         s << nVersion;
         s << ((unsigned char)32);
         s << nKey;
         s << nNew;
         s << nTried;
 
-        int nUBuckets = ADDRMAN_NEW_BUCKET_COUNT;
+        int nUBuckets = ADDRMAN_NEW_BUCKET_COUNT ^ (1 << 30);
         s << nUBuckets;
         std::map<int, int> mapUnkIds;
         int nIds = 0;
         for (std::map<int, CAddrInfo>::const_iterator it = mapInfo.begin(); it != mapInfo.end(); it++) {
-            if (nIds == nNew) break; // this means nNew was wrong, oh ow
             mapUnkIds[(*it).first] = nIds;
             const CAddrInfo &info = (*it).second;
             if (info.nRefCount) {
+                assert(nIds != nNew); // this means nNew was wrong, oh ow
                 s << info;
                 nIds++;
             }
         }
         nIds = 0;
         for (std::map<int, CAddrInfo>::const_iterator it = mapInfo.begin(); it != mapInfo.end(); it++) {
-            if (nIds == nTried) break; // this means nTried was wrong, oh ow
             const CAddrInfo &info = (*it).second;
             if (info.fInTried) {
+                assert(nIds != nTried); // this means nTried was wrong, oh ow
                 s << info;
                 nIds++;
             }
         }
-        for (std::vector<std::set<int> >::const_iterator it = vvNew.begin(); it != vvNew.end(); it++) {
-            const std::set<int> &vNew = (*it);
-            int nSize = vNew.size();
+        for (int bucket = 0; bucket < ADDRMAN_NEW_BUCKET_COUNT; bucket++) {
+            int nSize = 0;
+            for (int i = 0; i < ADDRMAN_BUCKET_SIZE; i++) {
+                if (vvNew[bucket][i] != -1)
+                    nSize++;
+            }
             s << nSize;
-            for (std::set<int>::const_iterator it2 = vNew.begin(); it2 != vNew.end(); it2++) {
-                int nIndex = mapUnkIds[*it2];
-                s << nIndex;
+            for (int i = 0; i < ADDRMAN_BUCKET_SIZE; i++) {
+                if (vvNew[bucket][i] != -1) {
+                    int nIndex = mapUnkIds[vvNew[bucket][i]];
+                    s << nIndex;
+                }
             }
         }
     }
@@ -328,67 +329,97 @@ public:
     {
         LOCK(cs);
 
+        Clear();
+
         unsigned char nVersion;
         s >> nVersion;
         unsigned char nKeySize;
         s >> nKeySize;
-        if (nKeySize != 32) throw std::ios_base::failure("Incorrect keysize in addrman");
+        if (nKeySize != 32) throw std::ios_base::failure("Incorrect keysize in addrman deserialization");
         s >> nKey;
         s >> nNew;
         s >> nTried;
-
         int nUBuckets = 0;
         s >> nUBuckets;
-        nIdCount = 0;
-        mapInfo.clear();
-        mapAddr.clear();
-        vRandom.clear();
-        vvTried = std::vector<std::vector<int> >(ADDRMAN_TRIED_BUCKET_COUNT, std::vector<int>(0));
-        vvNew = std::vector<std::set<int> >(ADDRMAN_NEW_BUCKET_COUNT, std::set<int>());
+        if (nVersion != 0) {
+            nUBuckets ^= (1 << 30);
+        }
+
+        // Deserialize entries from the new table.
         for (int n = 0; n < nNew; n++) {
             CAddrInfo &info = mapInfo[n];
             s >> info;
             mapAddr[info] = n;
             info.nRandomPos = vRandom.size();
             vRandom.push_back(n);
-            if (nUBuckets != ADDRMAN_NEW_BUCKET_COUNT) {
-                vvNew[info.GetNewBucket(nKey)].insert(n);
-                info.nRefCount++;
+            if (nVersion != 1 || nUBuckets != ADDRMAN_NEW_BUCKET_COUNT) {
+                // In case the new table data cannot be used (nVersion unknown, or bucket count wrong),
+                // immediately try to give them a reference based on their primary source address.
+                int nUBucket = info.GetNewBucket(nKey);
+                int nUBucketPos = info.GetBucketPosition(nKey, true, nUBucket);
+                if (vvNew[nUBucket][nUBucketPos] == -1) {
+                    vvNew[nUBucket][nUBucketPos] = n;
+                    info.nRefCount++;
+                }
             }
         }
         nIdCount = nNew;
+
+        // Deserialize entries from the tried table.
         int nLost = 0;
         for (int n = 0; n < nTried; n++) {
             CAddrInfo info;
             s >> info;
-            std::vector<int> &vTried = vvTried[info.GetTriedBucket(nKey)];
-            if (vTried.size() < ADDRMAN_TRIED_BUCKET_SIZE) {
+            int nKBucket = info.GetTriedBucket(nKey);
+            int nKBucketPos = info.GetBucketPosition(nKey, false, nKBucket);
+            if (vvTried[nKBucket][nKBucketPos] == -1) {
                 info.nRandomPos = vRandom.size();
                 info.fInTried = true;
                 vRandom.push_back(nIdCount);
                 mapInfo[nIdCount] = info;
                 mapAddr[info] = nIdCount;
-                vTried.push_back(nIdCount);
+                vvTried[nKBucket][nKBucketPos] = nIdCount;
                 nIdCount++;
             } else {
                 nLost++;
             }
         }
         nTried -= nLost;
-        for (int b = 0; b < nUBuckets; b++) {
-            std::set<int> &vNew = vvNew[b];
+
+        // Deserialize positions in the new table (if possible).
+        for (int bucket = 0; bucket < nUBuckets; bucket++) {
             int nSize = 0;
             s >> nSize;
             for (int n = 0; n < nSize; n++) {
                 int nIndex = 0;
                 s >> nIndex;
-                CAddrInfo &info = mapInfo[nIndex];
-                if (nUBuckets == ADDRMAN_NEW_BUCKET_COUNT && info.nRefCount < ADDRMAN_NEW_BUCKETS_PER_ADDRESS) {
-                    info.nRefCount++;
-                    vNew.insert(nIndex);
+                if (nIndex >= 0 && nIndex < nNew) {
+                    CAddrInfo &info = mapInfo[nIndex];
+                    int nUBucketPos = info.GetBucketPosition(nKey, true, bucket);
+                    if (nVersion == 1 && nUBuckets == ADDRMAN_NEW_BUCKET_COUNT && vvNew[bucket][nUBucketPos] == -1 && info.nRefCount < ADDRMAN_NEW_BUCKETS_PER_ADDRESS) {
+                        info.nRefCount++;
+                        vvNew[bucket][nUBucketPos] = nIndex;
+                    }
                 }
             }
         }
+
+        // Prune new entries with refcount 0 (as a result of collisions).
+        int nLostUnk = 0;
+        for (std::map<int, CAddrInfo>::const_iterator it = mapInfo.begin(); it != mapInfo.end(); ) {
+            if (it->second.fInTried == false && it->second.nRefCount == 0) {
+                std::map<int, CAddrInfo>::const_iterator itCopy = it++;
+                Delete(itCopy->first);
+                nLostUnk++;
+            } else {
+                it++;
+            }
+        }
+        if (nLost + nLostUnk > 0) {
+            LogPrint("addrman", "addrman lost %i new and %i tried addresses due to collisions\n", nLostUnk, nLost);
+        }
+
+        Check();
     }
 
     unsigned int GetSerializeSize(int nType, int nVersion) const
@@ -396,18 +427,34 @@ public:
         return (CSizeComputer(nType, nVersion) << *this).size();
     }
 
-    CAddrMan() : vRandom(0), vvTried(ADDRMAN_TRIED_BUCKET_COUNT, std::vector<int>(0)), vvNew(ADDRMAN_NEW_BUCKET_COUNT, std::set<int>())
+    void Clear()
     {
-         nKey = GetRandHash();
+        std::vector<int>().swap(vRandom);
+        nKey = GetRandHash();
+        for (size_t bucket = 0; bucket < ADDRMAN_NEW_BUCKET_COUNT; bucket++) {
+            for (size_t entry = 0; entry < ADDRMAN_BUCKET_SIZE; entry++) {
+                vvNew[bucket][entry] = -1;
+            }
+        }
+        for (size_t bucket = 0; bucket < ADDRMAN_TRIED_BUCKET_COUNT; bucket++) {
+            for (size_t entry = 0; entry < ADDRMAN_BUCKET_SIZE; entry++) {
+                vvTried[bucket][entry] = -1;
+            }
+        }
 
-         nIdCount = 0;
-         nTried = 0;
-         nNew = 0;
+        nIdCount = 0;
+        nTried = 0;
+        nNew = 0;
+    }
+
+    CAddrMan()
+    {
+        Clear();
     }
 
     ~CAddrMan()
     {
-         nKey.SetNull();
+        nKey.SetNull();
     }
 
     //! Return the number of (unique) addresses in all tables.