jadepy: do not use the legacy flow for non-AE signing

Prior to this change, requesting non-AE signing would use the legacy
flow which is deprecated. We now instead use the AE flow without
opting-in to AE signatures, and return the results in the format that
the legacy flow did (i.e. just the signatures with no signer commitments).

This change is API compatible(*), and means that jadepy users will no
longer use the legacy flow which will facilitate its removal in the future.

However, we still need to be able to test the legacy flow until its
removal. Add a 'use_legacy' parameter to enable this specifically for
test_jade.py to use.

(*) There is a small difference: if legacy signing was used, AE host
data could previously be passed and would be ignored - this is now an
error. If a caller is affected it can only mean either (a) they
intended to use AE signing but are not, or (b) they are not validating
the resulting AE signatures (because they are not receiving signer
commitments). Both need to be fixed by the caller, and this is
unavoidable if we wish to make Schnorr AE signing available later.

jadepy/jade.py

@@ -1642,7 +1642,7 @@ def _send_tx_inputs(self, base_id, inputs, use_ae_signatures=False, use_legacy=F
         The signatures are either in DER format with the sighash appended, or
         (for taproot inputs) 64/65 byte BIP 0341 Schnorr signatures.
         """
-        if use_ae_signatures:
+        if not use_legacy:
             # Anti-exfil protocol:
             # We send one message per input (which includes host-commitment *but
             # not* the host entropy) and receive the signer-commitment in reply.
@@ -1655,7 +1655,12 @@ def _send_tx_inputs(self, base_id, inputs, use_ae_signatures=False, use_legacy=F
             for txinput in inputs:
                 # ae-protocol - do not send the host entropy immediately
                 txinput = txinput.copy() if txinput else {}  # shallow copy
-                host_ae_entropy_values.append(txinput.pop('ae_host_entropy', None))
+                ae_host_entropy = txinput.pop('ae_host_entropy', None)
+                if not use_ae_signatures:
+                    if ae_host_entropy or txinput.get('ae_host_commitment', None):
+                        msg = 'Anti-Exfil host data present but use_ae_signatures=false'
+                        raise JadeError(1, msg, 'tx_input')
+                host_ae_entropy_values.append(ae_host_entropy)
 
                 base_id += 1
                 input_id = str(base_id)
@@ -1672,7 +1677,12 @@ def _send_tx_inputs(self, base_id, inputs, use_ae_signatures=False, use_legacy=F
                 signatures.append(reply)
 
             assert len(signatures) == len(inputs)
-            return list(zip(signer_commitments, signatures))
+            if use_ae_signatures:
+                return list(zip(signer_commitments, signatures))
+            # Since AE host data was not allowed, we should not have
+            # received any signer commitments
+            assert all(not sc for sc in signer_commitments)
+            return signatures
         else:
             # Legacy protocol:
             # We send one message per input - without expecting replies.
@@ -1681,7 +1691,8 @@ def _send_tx_inputs(self, base_id, inputs, use_ae_signatures=False, use_legacy=F
             # Then receive all n replies for the n signatures.
             # NOTE: *NOT* a sequence of n blocking rpc calls.
             # NOTE: at some point this flow should be removed in favour of the one
-            # above, albeit without passing anti-exfil entropy or commitment data.
+            # above.
+            assert not use_ae_signatures, 'Can not use Anti-Exfil with legacy sign_tx'
 
             # Send all n inputs
             requests = []
@@ -1815,7 +1826,7 @@ def sign_liquid_tx(self, network, txn, inputs, commitments, change, use_ae_signa
                   'txn': txn,
                   'num_inputs': len(inputs),
                   'trusted_commitments': commitments,
-                  'use_ae_signatures': use_ae_signatures,
+                  'use_ae_signatures': not use_legacy,
                   'change': change,
                   'asset_info': asset_info,
                   'additional_info': additional_info}
@@ -1900,7 +1911,7 @@ def sign_tx(self, network, txn, inputs, change, use_ae_signatures=False, use_leg
         params = {'network': network,
                   'txn': txn,
                   'num_inputs': len(inputs),
-                  'use_ae_signatures': use_ae_signatures,
+                  'use_ae_signatures': not use_legacy,
                   'change': change}
 
         reply = self._jadeRpc('sign_tx', params, str(base_id))