Add fingerprinting countermeasures part

Author: jonasschnelli

bip-0159.mediawiki

@@ -42,6 +42,10 @@ A safety buffer of additional 144 blocks to handle chain reorganizations <I>SHOU
 
 Full nodes following this BIP <I>SHOULD</I> relay address/services (<code>addr</code> message) from peers they would connect to (including peers signaling <code>NODE_NETWORK_LIMITED_*</code>).
 
+=== Counter-measures for peer fingerprinting ===
+
+Peers may have different prune depths (depending on the peers configuration, disk space, etc.) which can result in a fingerprinting weakness (finding the prune depth through getdata requests). NODE_NETWORK_LIMITED supporting peers <I>SHOULD</I> avoid leaking the prune depth and therefore not serve blocks deeper then the signaled <code>NODE_NETWORK_LIMITED_*</code> thresholds.
+
 === Risks ===
 
 Pruned peers following this BIP may consume more outbound bandwidth.