Add changed block hashing scheme.

Author: td202

updates/P7.txt

@@ -110,6 +110,12 @@ supported shielded transfers (also known as encrypted transfers).
 This mechanism allows an account to "shield" part of its balance, 
 cryptographically encrypting it so that the amount cannot be inspected
 except by the owner of the account (using its secret encryption key).
+(It is possible for a sufficient combination of identity disclosure
+authorities (e.g. 2 of 3) to act in concert with the identity provider
+for an account to recover the secret encryption key (for instance, if
+compelled to do so by legal authorities) and thus decrypt the shielded
+balance and transfers on that account.)
+
 An account can transfer an amount from its shielded balance to another
 account. While the sender and receiver are publicly visible, the exact
 amount transferred (in CCD) is not. An account can also decrypt funds from