net: merge V2Transport constructors, move key gen

This removes the ability for BIP324Cipher to generate its own key, moving that
responsibility to the caller (mostly, V2Transport). This allows us to write
the random-key V2Transport constructor by delegating to the explicit-key one.

src/bip324.cpp

@@ -22,13 +22,6 @@
 #include <iterator>
 #include <string>
 
-BIP324Cipher::BIP324Cipher() noexcept
-{
-    m_key.MakeNewKey(true);
-    uint256 entropy = GetRandHash();
-    m_our_pubkey = m_key.EllSwiftCreate(MakeByteSpan(entropy));
-}
-
 BIP324Cipher::BIP324Cipher(const CKey& key, Span<const std::byte> ent32) noexcept :
     m_key(key)
 {

src/bip324.h

@@ -41,8 +41,8 @@ class BIP324Cipher
     std::array<std::byte, GARBAGE_TERMINATOR_LEN> m_recv_garbage_terminator;
 
 public:
-    /** Initialize a BIP324 cipher with securely generated random keys. */
-    BIP324Cipher() noexcept;
+    /** No default constructor; keys must be provided to create a BIP324Cipher. */
+    BIP324Cipher() = delete;
 
     /** Initialize a BIP324 cipher with specified key and encoding entropy (testing only). */
     BIP324Cipher(const CKey& key, Span<const std::byte> ent32) noexcept;

src/net.cpp

@@ -979,23 +979,24 @@ class V2MessageMap
 
 const V2MessageMap V2_MESSAGE_MAP;
 
-} // namespace
+CKey GenerateRandomKey() noexcept
+{
+    CKey key;
+    key.MakeNewKey(/*fCompressed=*/true);
+    return key;
+}
 
-V2Transport::V2Transport(NodeId nodeid, bool initiating, int type_in, int version_in) noexcept :
-    m_cipher{}, m_initiating{initiating}, m_nodeid{nodeid},
-    m_v1_fallback{nodeid, type_in, version_in}, m_recv_type{type_in}, m_recv_version{version_in},
-    m_recv_state{initiating ? RecvState::KEY : RecvState::KEY_MAYBE_V1},
-    m_send_state{initiating ? SendState::AWAITING_KEY : SendState::MAYBE_V1}
+std::vector<uint8_t> GenerateRandomGarbage() noexcept
 {
-    // Construct garbage (including its length) using a FastRandomContext.
+    std::vector<uint8_t> ret;
     FastRandomContext rng;
-    size_t garbage_len = rng.randrange(MAX_GARBAGE_LEN + 1);
-    // Initialize the send buffer with ellswift pubkey + garbage.
-    m_send_buffer.resize(EllSwiftPubKey::size() + garbage_len);
-    std::copy(std::begin(m_cipher.GetOurPubKey()), std::end(m_cipher.GetOurPubKey()), MakeWritableByteSpan(m_send_buffer).begin());
-    rng.fillrand(MakeWritableByteSpan(m_send_buffer).subspan(EllSwiftPubKey::size()));
+    ret.resize(rng.randrange(V2Transport::MAX_GARBAGE_LEN + 1));
+    rng.fillrand(MakeWritableByteSpan(ret));
+    return ret;
 }
 
+} // namespace
+
 V2Transport::V2Transport(NodeId nodeid, bool initiating, int type_in, int version_in, const CKey& key, Span<const std::byte> ent32, Span<const uint8_t> garbage) noexcept :
     m_cipher{key, ent32}, m_initiating{initiating}, m_nodeid{nodeid},
     m_v1_fallback{nodeid, type_in, version_in}, m_recv_type{type_in}, m_recv_version{version_in},
@@ -1009,6 +1010,10 @@ V2Transport::V2Transport(NodeId nodeid, bool initiating, int type_in, int versio
     std::copy(garbage.begin(), garbage.end(), m_send_buffer.begin() + EllSwiftPubKey::size());
 }
 
+V2Transport::V2Transport(NodeId nodeid, bool initiating, int type_in, int version_in) noexcept :
+    V2Transport{nodeid, initiating, type_in, version_in, GenerateRandomKey(),
+                MakeByteSpan(GetRandHash()), GenerateRandomGarbage()} { }
+
 void V2Transport::SetReceiveState(RecvState recv_state) noexcept
 {
     AssertLockHeld(m_recv_mutex);

src/test/net_tests.cpp

@@ -1008,6 +1008,14 @@ BOOST_AUTO_TEST_CASE(advertise_local_address)
 
 namespace {
 
+CKey GenerateRandomTestKey() noexcept
+{
+    CKey key;
+    uint256 key_data = InsecureRand256();
+    key.Set(key_data.begin(), key_data.end(), true);
+    return key;
+}
+
 /** A class for scenario-based tests of V2Transport
  *
  * Each V2TransportTester encapsulates a V2Transport (the one being tested), and can be told to
@@ -1031,6 +1039,7 @@ class V2TransportTester
     /** Construct a tester object. test_initiator: whether the tested transport is initiator. */
     V2TransportTester(bool test_initiator) :
         m_transport(0, test_initiator, SER_NETWORK, INIT_PROTO_VERSION),
+        m_cipher{GenerateRandomTestKey(), MakeByteSpan(InsecureRand256())},
         m_test_initiator(test_initiator) {}
 
     /** Data type returned by Interact: