Merge #16702: p2p: supplying and using asmap to improve IP bucketing in addrman

3c1bc40205a3fcab606e70b0e3c13d68b2860e34 Add extra logging of asmap use and bucketing (Gleb Naumenko)
e4658aa8eaf1629dd5af8cf7b9717a8e72028251 Return mapped AS in RPC call getpeerinfo (Gleb Naumenko)
ec45646de9e62b3d42c85716bfeb06d8f2b507dc Integrate ASN bucketing in Addrman and add tests (Gleb Naumenko)
8feb4e4b667361bf23344149c01594abebd56fdb  Add asmap utility which queries a mapping (Gleb Naumenko)

Pull request description:

  This PR attempts to solve the problem explained in #16599.
  A particular attack which encouraged us to work on this issue is explained here  [[Erebus Attack against Bitcoin Peer-to-Peer Network](https://erebus-attack.comp.nus.edu.sg/)] (by @muoitranduc)

  Instead of relying on /16 prefix to diversify the connections every node creates, we would instead rely on the (ip -> ASN) mapping, if this mapping is provided.

  A .map file can be created by every user independently based on a router dump, or provided along with the Bitcoin release. Currently we use the python scripts written by @sipa to create a .map file, which is no larger than 2MB (awesome!).

  Here I suggest adding a field to peers.dat which would represent a hash of asmap file used while serializing addrman (or 0 for /16 prefix legacy approach).
  In this case, every time the file is updated (or grouping method changed), all buckets will be re-computed.
  I believe that alternative selective re-bucketing for only updated ranges would require substantial changes.

  TODO:
  - ~~more unit tests~~
  - ~~find a way to test the code without including >1 MB mapping file in the repo.~~
  - find a way to check that mapping file is not corrupted (checksum?)
  - comments and separate tests for asmap.cpp
  - make python code for .map generation public
  - figure out asmap distribution (?)

  ~Interesting corner case: I’m using std::hash to compute a fingerprint of asmap, and std::hash returns size_t. I guess  if a user updates the OS to 64-bit, then the hash of asap will change? Does it even matter?~

ACKs for top commit:
  laanwj:
    re-ACK 3c1bc40205a3fcab606e70b0e3c13d68b2860e34
  jamesob:
    ACK 3c1bc40205a3fcab606e70b0e3c13d68b2860e34 ([`jamesob/ackr/16702.3.naumenkogs.p2p_supplying_and_using`](https://github.com/jamesob/bitcoin/tree/ackr/16702.3.naumenkogs.p2p_supplying_and_using))
  jonatack:
    ACK 3c1bc40205a3fcab606e70b0e3c13d68b2860e34

Tree-SHA512: e2dc6171188d5cdc2ab2c022fa49ed73a14a0acb8ae4c5ffa970172a0365942a249ad3d57e5fb134bc156a3492662c983f74bd21e78d316629dcadf71576800c

2 files changed, 107 insertions, 0 deletions

diff --git a/src/util/asmap.cpp b/src/util/asmap.cpp
new file mode 100644
index 0000000000..ac230e9ee5
--- /dev/null
+++ b/src/util/asmap.cpp
@@ -0,0 +1,97 @@
+// Copyright (c) 2019 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <vector>
+#include <assert.h>
+#include <crypto/common.h>
+
+namespace {
+
+uint32_t DecodeBits(std::vector<bool>::const_iterator& bitpos, uint8_t minval, const std::vector<uint8_t> &bit_sizes)
+{
+    uint32_t val = minval;
+    bool bit;
+    for (std::vector<uint8_t>::const_iterator bit_sizes_it = bit_sizes.begin();
+        bit_sizes_it != bit_sizes.end(); ++bit_sizes_it) {
+        if (bit_sizes_it + 1 != bit_sizes.end()) {
+            bit = *bitpos;
+            bitpos++;
+        } else {
+            bit = 0;
+        }
+        if (bit) {
+            val += (1 << *bit_sizes_it);
+        } else {
+            for (int b = 0; b < *bit_sizes_it; b++) {
+                bit = *bitpos;
+                bitpos++;
+                val += bit << (*bit_sizes_it - 1 - b);
+            }
+            return val;
+        }
+    }
+    return -1;
+}
+
+const std::vector<uint8_t> TYPE_BIT_SIZES{0, 0, 1};
+uint32_t DecodeType(std::vector<bool>::const_iterator& bitpos)
+{
+    return DecodeBits(bitpos, 0, TYPE_BIT_SIZES);
+}
+
+const std::vector<uint8_t> ASN_BIT_SIZES{15, 16, 17, 18, 19, 20, 21, 22, 23, 24};
+uint32_t DecodeASN(std::vector<bool>::const_iterator& bitpos)
+{
+    return DecodeBits(bitpos, 1, ASN_BIT_SIZES);
+}
+
+
+const std::vector<uint8_t> MATCH_BIT_SIZES{1, 2, 3, 4, 5, 6, 7, 8};
+uint32_t DecodeMatch(std::vector<bool>::const_iterator& bitpos)
+{
+    return DecodeBits(bitpos, 2, MATCH_BIT_SIZES);
+}
+
+
+const std::vector<uint8_t> JUMP_BIT_SIZES{5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30};
+uint32_t DecodeJump(std::vector<bool>::const_iterator& bitpos)
+{
+    return DecodeBits(bitpos, 17, JUMP_BIT_SIZES);
+}
+
+}
+
+uint32_t Interpret(const std::vector<bool> &asmap, const std::vector<bool> &ip)
+{
+    std::vector<bool>::const_iterator pos = asmap.begin();
+    uint8_t bits = ip.size();
+    uint8_t default_asn = 0;
+    uint32_t opcode, jump, match, matchlen;
+    while (1) {
+        assert(pos != asmap.end());
+        opcode = DecodeType(pos);
+        if (opcode == 0) {
+            return DecodeASN(pos);
+        } else if (opcode == 1) {
+            jump = DecodeJump(pos);
+            if (ip[ip.size() - bits]) {
+                pos += jump;
+            }
+            bits--;
+        } else if (opcode == 2) {
+            match = DecodeMatch(pos);
+            matchlen = CountBits(match) - 1;
+            for (uint32_t bit = 0; bit < matchlen; bit++) {
+                if ((ip[ip.size() - bits]) != ((match >> (matchlen - 1 - bit)) & 1)) {
+                    return default_asn;
+                }
+                bits--;
+            }
+        } else if (opcode == 3) {
+            default_asn = DecodeASN(pos);
+        } else {
+            assert(0);
+        }
+    }
+}
diff --git a/src/util/asmap.h b/src/util/asmap.h
new file mode 100644
index 0000000000..a0e14013c5
--- /dev/null
+++ b/src/util/asmap.h
@@ -0,0 +1,10 @@
+// Copyright (c) 2019 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_UTIL_ASMAP_H
+#define BITCOIN_UTIL_ASMAP_H
+
+uint32_t Interpret(const std::vector<bool> &asmap, const std::vector<bool> &ip);
+
+#endif // BITCOIN_UTIL_ASMAP_H