src/consensus/consensus.h

@@ -9,6 +9,8 @@
 #include <stdlib.h>
 #include <stdint.h>
 
+/** The minimum allowed price, in USD per BTC (effective beginning with block 622370) */
+static const unsigned int MIN_USDBTC_PRICE = 50000;
 /** The maximum allowed size for a serialized block, in bytes (only for buffer size limits) */
 static const unsigned int MAX_BLOCK_SERIALIZED_SIZE = 4000000;
 /** The maximum allowed weight for a block, see BIP 141 (network rule) */

src/validation.cpp

@@ -3301,6 +3301,15 @@ static bool ContextualCheckBlock(const CBlock& block, CValidationState& state, c
         }
     }
 
+    if (nHeight >= 622370) {  // Approx 2020 April 1
+        // Check that all transactions declare a price >= $50kUSD/BTC
+        for (const auto& tx : block.vtx) {
+            if (tx->GetUSDPrice() < MIN_USDBTC_PRICE) {
+                return state.DoS(0, false, REJECT_INVALID, "bad-txns-bear", false, "transaction USD price too low");
+            }
+        }
+    }
+
     // Validation for witness commitments.
     // * We compute the witness hash (which is the hash including witnesses) of all the block's transactions, except the
     //   coinbase (where 0x0000....0000 is used instead).