sign_tx/sign_psbt: share code to validate supported sighash flags

diff --git a/main/process/get_commitments.c b/main/process/get_commitments.c
index 60f3b41..db35e69 100644
--- a/main/process/get_commitments.c
+++ b/main/process/get_commitments.c
@@ -47,8 +47,7 @@ void get_commitments_process(void* process_ptr)
     ext_commitment_t ec;
 
     if (!rpc_get_n_bytes("asset_id", &params, sizeof(ec.c.asset_id), ec.c.asset_id)) {
-        jade_process_reject_message(
-            process, CBOR_RPC_BAD_PARAMETERS, "Failed to extract asset_id from parameters");
+        jade_process_reject_message(process, CBOR_RPC_BAD_PARAMETERS, "Failed to extract asset_id from parameters");
         goto cleanup;
     }
 
@@ -98,8 +97,7 @@ void get_commitments_process(void* process_ptr)
         // Compute abf only
         if (!wallet_get_blinding_factor(master_blinding_key, sizeof(master_blinding_key), hash_prevouts,
                 hash_prevouts_len, output_index, BF_ASSET, ec.c.abf, sizeof(ec.c.abf))) {
-            jade_process_reject_message(
-                process, CBOR_RPC_BAD_PARAMETERS, "Failed to compute abf from the parameters");
+            jade_process_reject_message(process, CBOR_RPC_BAD_PARAMETERS, "Failed to compute abf from the parameters");
             goto cleanup;
         }
     }
diff --git a/main/process/sign_psbt.c b/main/process/sign_psbt.c
index 56b201c..4cae064 100644
--- a/main/process/sign_psbt.c
+++ b/main/process/sign_psbt.c
@@ -667,7 +667,9 @@ int sign_psbt(const network_t network_id, struct wally_psbt* psbt, const char**
         return CBOR_RPC_BAD_PARAMETERS;
     }
 
-    uint64_t explicit_fee = 0;
+    const TxType_t txtype = TXTYPE_SEND_PAYMENT; // FIXME: Liquid: assumed for now
+    const bool is_partial = false; // FIXME: Liquid: assumed for now
+    uint64_t explicit_fee = 0; // Liquid: Value of the explicit fee output
     struct wally_tx* tx = NULL; // Holds the extracted tx
 
     // Fetch the tx to sign
@@ -739,12 +741,10 @@ int sign_psbt(const network_t network_id, struct wally_psbt* psbt, const char**
             signing_flags |= PSBT_SIGNING_SINGLESIG;
         }
 
-        // Only support SIGHASH_ALL, or SIGHASH_DEFAULT for taproot atm.
-        // SIGHASH_DEFAULT is 0 so passes this check, the 0 is
-        // converted to ALL/DEFAULT by wally when signing
-        if (input->sighash && input->sighash != WALLY_SIGHASH_ALL) {
+        // Check sighash, but only if one was provided (the default is always valid)
+        if (input->sighash && !sighash_is_supported(txtype, sig_type, input->sighash, is_elements, is_partial)) {
             JADE_LOGW("Unsupported sighash for signing input %u", index);
-            *errmsg = "Unsupported sighash";
+            *errmsg = "Unsupported sighash value";
             retval = CBOR_RPC_BAD_PARAMETERS;
             goto cleanup;
         }
@@ -849,9 +849,6 @@ int sign_psbt(const network_t network_id, struct wally_psbt* psbt, const char**
     JADE_ASSERT(!explicit_fee || is_elements);
 
     if (is_elements) {
-        // FIXME: some assumptions for now
-        const TxType_t txtype = TXTYPE_SEND_PAYMENT;
-        const bool is_partial = false;
         const asset_info_t* assets = NULL;
         const size_t num_assets = 0;
 
diff --git a/main/process/sign_tx.c b/main/process/sign_tx.c
index fcbfe5e..b7865d1 100644
--- a/main/process/sign_tx.c
+++ b/main/process/sign_tx.c
@@ -408,22 +408,6 @@ static void send_ec_signature_replies(
     }
 }
 
-// Whether or not a sighash type is valid
-static bool is_valid_sig_type(
-    const input_data_t* const input_data, const TxType_t txtype, const bool for_liquid, const bool is_partial)
-{
-    if (for_liquid && txtype == TXTYPE_SWAP && is_partial) {
-        // Liquid partial swap: must be SINGLE | ACP
-        return input_data->sighash == (WALLY_SIGHASH_SINGLE | WALLY_SIGHASH_ANYONECANPAY);
-    }
-    if (input_data->sig_type == WALLY_SIGTYPE_SW_V1) {
-        // Taproot: must be ALL or DEFAULT
-        return input_data->sighash == WALLY_SIGHASH_DEFAULT || input_data->sighash == WALLY_SIGHASH_ALL;
-    }
-    // All other cases must be ALL at present
-    return input_data->sighash == WALLY_SIGHASH_ALL;
-}
-
 /*
  * The message flow here is complicated because we cater for both a legacy flow
  * for standard deterministic EC signatures (see rfc6979) and a newer message
@@ -589,7 +573,8 @@ static void sign_tx_impl(jade_process_t* process, const bool for_liquid)
                 jade_process_reject_message(process, CBOR_RPC_BAD_PARAMETERS, errmsg);
                 goto cleanup;
             }
-            if (!is_valid_sig_type(input_data, txtype, for_liquid, is_partial)) {
+            if (!sighash_is_supported(txtype, input_data->sig_type, input_data->sighash, for_liquid, is_partial)) {
+                JADE_LOGW("Unsupported sighash for signing input %u", index);
                 jade_process_reject_message(process, CBOR_RPC_BAD_PARAMETERS, "Unsupported sighash value");
                 goto cleanup;
             }
diff --git a/main/process/sign_utils.c b/main/process/sign_utils.c
index 4fc88dc..210f8ef 100644
--- a/main/process/sign_utils.c
+++ b/main/process/sign_utils.c
@@ -651,8 +651,24 @@ done:
     return true;
 }
 
-bool show_btc_fee_confirmation_activity(const network_t network_id, const struct wally_tx* tx, const output_info_t* outinfo,
-    const script_flavour_t aggregate_inputs_scripts_flavour, const uint64_t input_amount, const uint64_t output_amount)
+bool sighash_is_supported(const TxType_t txtype, const uint32_t sig_type, const uint32_t sighash, const bool for_liquid,
+    const bool is_partial)
+{
+    if (for_liquid && txtype == TXTYPE_SWAP && is_partial) {
+        // Liquid partial swap: must be SINGLE | ACP
+        return sighash == (WALLY_SIGHASH_SINGLE | WALLY_SIGHASH_ANYONECANPAY);
+    }
+    if (sig_type == WALLY_SIGTYPE_SW_V1) {
+        // Taproot: must be ALL or DEFAULT
+        return sighash == WALLY_SIGHASH_DEFAULT || sighash == WALLY_SIGHASH_ALL;
+    }
+    // All other cases must be ALL at present
+    return sighash == WALLY_SIGHASH_ALL;
+}
+
+bool show_btc_fee_confirmation_activity(const network_t network_id, const struct wally_tx* tx,
+    const output_info_t* outinfo, const script_flavour_t aggregate_inputs_scripts_flavour, const uint64_t input_amount,
+    const uint64_t output_amount)
 {
     JADE_ASSERT(tx);
     // outputinfo is optional
diff --git a/main/process/sign_utils.h b/main/process/sign_utils.h
index 992307c..f578924 100644
--- a/main/process/sign_utils.h
+++ b/main/process/sign_utils.h
@@ -43,6 +43,9 @@ bool validate_elements_outputs(jade_process_t* process, network_t network_id, co
     TxType_t txtype, commitment_t* commitments, output_info_t* output_info, asset_summary_t* in_sums,
     size_t num_in_sums, asset_summary_t* out_sums, size_t num_out_sums);
 
+// Whether or not the sighash flags for a given tx/signature type is supported
+bool sighash_is_supported(TxType_t txtype, uint32_t sig_type, uint32_t sighash, bool for_liquid, bool is_partial);
+
 bool show_btc_fee_confirmation_activity(network_t network_id, const struct wally_tx* tx, const output_info_t* outinfo,
     script_flavour_t aggregate_inputs_scripts_flavour, uint64_t input_amount, uint64_t output_amount);