better comment on strange padding

// FREEBIE

src/Devices/OWSVerificationStateSyncMessage.m

@@ -66,6 +66,12 @@ NS_ASSUME_NONNULL_BEGIN
     verifiedBuilder.state = OWSVerificationStateToProtoState(self.verificationState);
 
     OWSAssert(self.paddingBytesLength != 0);
+
+    // We add the same amount of padding in the VerificationStateSync message and it's coresponding NullMessage so that
+    // the sync message is indistinguishable from an outgoing Sent transcript corresponding to the NullMessage. We pad
+    // the NullMessage so as to obscure it's content. The sync message (like all sync messages) will be *additionally*
+    // padded by the superclass while being sent. The end result is we send a NullMessage of a non-distinct size, and a
+    // verification sync which is ~1-512 bytes larger then that.
     verifiedBuilder.nullMessage = [Cryptography generateRandomBytes:self.paddingBytesLength];
     
     syncMessageBuilder.verifiedBuilder = verifiedBuilder;

src/Messages/OWSOutgoingNullMessage.m

@@ -43,6 +43,12 @@ NS_ASSUME_NONNULL_BEGIN
     NSUInteger contentLength = self.verificationStateSyncMessage.unpaddedVerifiedLength;
 
     OWSAssert(self.verificationStateSyncMessage.paddingBytesLength > 0);
+
+    // We add the same amount of padding in the VerificationStateSync message and it's coresponding NullMessage so that
+    // the sync message is indistinguishable from an outgoing Sent transcript corresponding to the NullMessage. We pad
+    // the NullMessage so as to obscure it's content. The sync message (like all sync messages) will be *additionally*
+    // padded by the superclass while being sent. The end result is we send a NullMessage of a non-distinct size, and a
+    // verification sync which is ~1-512 bytes larger then that.
     contentLength += self.verificationStateSyncMessage.paddingBytesLength;
 
     OWSAssert(contentLength > 0)