Export Casa pairing as a crypto-account QR

### extmod/foundation-rust/include/foundation.h
@@ -421,6 +421,18 @@ typedef struct {
   bool has_passport_firmware_version;
 } UR_PassportResponse;
 
+/**
+ * A Casa `crypto-account` containing both supported registration keys.
+ */
+typedef struct {
+  uint32_t master_fingerprint;
+  uint64_t network;
+  uint8_t root_key_data[33];
+  uint8_t root_chain_code[32];
+  uint8_t casa_key_data[33];
+  uint8_t casa_chain_code[32];
+} UR_CryptoAccount;
+
 /**
  * A uniform resource.
  */
@@ -445,6 +457,10 @@ typedef enum {
    * Passport custom `x-passport-response`.
    */
   PassportResponse,
+  /**
+   * Casa wallet-registration `crypto-account`.
+   */
+  CryptoAccount,
 } UR_Value_Tag;
 
 typedef struct {
@@ -471,6 +487,9 @@ typedef struct {
     struct {
       UR_PassportResponse passport_response;
     };
+    struct {
+      UR_CryptoAccount crypto_account;
+    };
   };
 } UR_Value;
 
@@ -665,6 +684,17 @@ void ur_registry_new_derived_key(UR_Value *value,
                                  const UR_Keypath *origin,
                                  uint32_t parent_fingerprint);
 
+/**
+ * Create the Casa wallet-registration `crypto-account` UR.
+ */
+void ur_registry_new_crypto_account(UR_Value *value,
+                                    const uint8_t (*root_key_data)[33],
+                                    const uint8_t (*root_chain_code)[32],
+                                    const uint8_t (*casa_key_data)[33],
+                                    const uint8_t (*casa_chain_code)[32],
+                                    uint32_t master_fingerprint,
+                                    uint64_t network);
+
 /**
  * Create a new `psbt` UR.
  */

### extmod/foundation-rust/src/ur/encoder.rs
@@ -107,21 +107,27 @@ pub unsafe extern "C" fn ur_encoder_start(
     value: &UR_Value,
     max_chars: usize,
 ) {
-    // SAFETY: The UR_Value can contain some raw pointers which need to be
-    // accessed in order to convert it to a `ur::registry::BaseValue` which
-    // is then encoded below, so the pointers lifetime only need to be valid
-    // for the scope of this function.
-    let value = unsafe { value.to_value() };
-
     // SAFETY: This code assumes that runs on a single thread.
     let message = unsafe { &mut *ptr::addr_of_mut!(UR_ENCODER_MESSAGE) };
 
     message.clear();
     let mut e = Encoder::new(Writer(message));
-    value.encode(&mut e, &mut ()).expect("Couldn't encode UR");
+    let ur_type = match value {
+        UR_Value::CryptoAccount(account) => {
+            account.encode(&mut e, &mut ()).expect("Couldn't encode UR");
+            crate::ur::registry::UR_CryptoAccount::UR_TYPE
+        }
+        _ => {
+            // SAFETY: Other UR values may contain pointers which remain valid
+            // for this call, as required by this function's contract.
+            let value = unsafe { value.to_value() };
+            value.encode(&mut e, &mut ()).expect("Couldn't encode UR");
+            value.ur_type()
+        }
+    };
 
     encoder.inner.start(
-        value.ur_type(),
+        ur_type,
         message,
         max_fragment_len(UR_MAX_TYPE, usize::MAX, max_chars),
     );

### extmod/foundation-rust/src/ur/registry.rs
@@ -14,6 +14,7 @@ use foundation_urtypes::{
     value,
     value::Value,
 };
+use minicbor::{data::Tag, encode::Write, Encode, Encoder};
 
 use uuid::Uuid;
 
@@ -38,6 +39,8 @@ pub enum UR_Value {
     PassportRequest(UR_PassportRequest),
     /// Passport custom `x-passport-response`.
     PassportResponse(UR_PassportResponse),
+    /// Casa wallet-registration `crypto-account`.
+    CryptoAccount(UR_CryptoAccount),
 }
 
 impl UR_Value {
@@ -90,6 +93,9 @@ impl UR_Value {
                 Value::Psbt(buf)
             }
             UR_Value::HDKey(v) => Value::HDKey(v.into()),
+            UR_Value::CryptoAccount(_) => panic!(
+                "CryptoAccount is encoded directly. Should be unreachable"
+            ),
             UR_Value::PassportRequest(_) => panic!(
                 "Not implemented as it isn't needed. Should be unreachable"
             ),
@@ -98,6 +104,99 @@ impl UR_Value {
     }
 }
 
+/// A Casa `crypto-account` containing both supported registration keys.
+#[derive(Debug)]
+#[repr(C)]
+pub struct UR_CryptoAccount {
+    pub master_fingerprint: u32,
+    pub network: u64,
+    pub root_key_data: [u8; 33],
+    pub root_chain_code: [u8; 32],
+    pub casa_key_data: [u8; 33],
+    pub casa_chain_code: [u8; 32],
+}
+
+impl UR_CryptoAccount {
+    pub const UR_TYPE: &'static str = "crypto-account";
+
+    const TAG_CRYPTO_OUTPUT: Tag = Tag::new(308);
+    const TAG_SCRIPT_HASH: Tag = Tag::new(400);
+    const TAG_WITNESS_PUBLIC_KEY_HASH: Tag = Tag::new(404);
+    const TAG_HDKEY_LEGACY: Tag = Tag::new(303);
+    const TAG_KEYPATH_LEGACY: Tag = Tag::new(304);
+    const TAG_COIN_INFO_LEGACY: Tag = Tag::new(305);
+
+    fn encode_output<W: Write>(
+        &self,
+        e: &mut Encoder<W>,
+        key_data: &[u8; 33],
+        chain_code: &[u8; 32],
+        casa_key: bool,
+    ) -> Result<(), minicbor::encode::Error<W::Error>> {
+        e.tag(Self::TAG_CRYPTO_OUTPUT)?
+            .tag(Self::TAG_SCRIPT_HASH)?
+            .tag(Self::TAG_WITNESS_PUBLIC_KEY_HASH)?
+            .tag(Self::TAG_HDKEY_LEGACY)?
+            .map(if casa_key { 5 } else { 4 })?
+            .u8(3)?
+            .bytes(key_data)?
+            .u8(4)?
+            .bytes(chain_code)?
+            .u8(5)?
+            .tag(Self::TAG_COIN_INFO_LEGACY)?;
+
+        if self.network == UR_NETWORK_MAINNET as u64 {
+            e.map(0)?;
+        } else {
+            e.map(1)?.u8(2)?.u64(self.network)?;
+        }
+
+        e.u8(6)?.tag(Self::TAG_KEYPATH_LEGACY)?.map(3)?.u8(1)?;
+        if casa_key {
+            e.array(2)?.u32(45)?.bool(true)?;
+        } else {
+            e.array(0)?;
+        }
+        e.u8(2)?
+            .u32(self.master_fingerprint)?
+            .u8(3)?
+            .u8(u8::from(casa_key))?;
+
+        if casa_key {
+            e.u8(8)?.u32(self.master_fingerprint)?;
+        }
+
+        Ok(())
+    }
+}
+
+impl<C> Encode<C> for UR_CryptoAccount {
+    fn encode<W: Write>(
+        &self,
+        e: &mut Encoder<W>,
+        _ctx: &mut C,
+    ) -> Result<(), minicbor::encode::Error<W::Error>> {
+        e.map(2)?
+            .u8(1)?
+            .u32(self.master_fingerprint)?
+            .u8(2)?
+            .array(2)?;
+        self.encode_output(
+            e,
+            &self.root_key_data,
+            &self.root_chain_code,
+            false,
+        )?;
+        self.encode_output(
+            e,
+            &self.casa_key_data,
+            &self.casa_chain_code,
+            true,
+        )?;
+        Ok(())
+    }
+}
+
 /// A `hdkey`.
 #[repr(C)]
 pub enum UR_HDKey {
@@ -445,6 +544,27 @@ pub extern "C" fn ur_registry_new_derived_key(
     }));
 }
 
+/// Create the Casa wallet-registration `crypto-account` UR.
+#[no_mangle]
+pub extern "C" fn ur_registry_new_crypto_account(
+    value: &mut UR_Value,
+    root_key_data: &[u8; 33],
+    root_chain_code: &[u8; 32],
+    casa_key_data: &[u8; 33],
+    casa_chain_code: &[u8; 32],
+    master_fingerprint: u32,
+    network: u64,
+) {
+    *value = UR_Value::CryptoAccount(UR_CryptoAccount {
+        master_fingerprint,
+        network,
+        root_key_data: *root_key_data,
+        root_chain_code: *root_chain_code,
+        casa_key_data: *casa_key_data,
+        casa_chain_code: *casa_chain_code,
+    });
+}
+
 /// Create a new `psbt` UR.
 #[no_mangle]
 pub extern "C" fn ur_registry_new_psbt(
@@ -476,3 +596,46 @@ pub extern "C" fn ur_registry_new_passport_response(
         has_passport_firmware_version: true,
     })
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use minicbor::encode::write::Cursor;
+
+    #[test]
+    fn casa_crypto_account_wire_format_is_pinned() {
+        let account = UR_CryptoAccount {
+            master_fingerprint: 0x1234_5678,
+            network: UR_NETWORK_MAINNET as u64,
+            root_key_data: [2; 33],
+            root_chain_code: [3; 32],
+            casa_key_data: [4; 33],
+            casa_chain_code: [5; 32],
+        };
+        let mut output = Cursor::new([0u8; 256]);
+        account
+            .encode(&mut Encoder::new(&mut output), &mut ())
+            .unwrap();
+
+        let expected = concat!(
+            "a2011a123456780282d90134d90190d90194d9012fa40358210202020202020202020202020202020202020202",
+            "020202020202020202020202020458200303030303030303030303030303030303030303030303030303030303",
+            "03030305d90131a006d90130a30180021a123456780300d90134d90190d90194d9012fa5035821040404040404",
+            "040404040404040404040404040404040404040404040404040404045820050505050505050505050505050505",
+            "050505050505050505050505050505050505d90131a006d90130a30182182df5021a123456780301081a123456",
+            "78",
+        );
+        let encoded = &output.get_ref()[..output.position()];
+        assert_eq!(encoded.len() * 2, expected.len());
+        for (actual, expected) in
+            encoded.iter().zip(expected.as_bytes().chunks_exact(2))
+        {
+            let nibble = |byte| match byte {
+                b'0'..=b'9' => byte - b'0',
+                b'a'..=b'f' => byte - b'a' + 10,
+                _ => unreachable!(),
+            };
+            assert_eq!(*actual, nibble(expected[0]) << 4 | nibble(expected[1]));
+        }
+    }
+}

### extmod/foundation/modfoundation-ur.h
@@ -92,6 +92,9 @@ STATIC void mod_foundation_ur_Value_print(const mp_print_t *print,
         case HDKey:
             mp_print_str(print, "UR_Value::HDKey");
             break;
+        case CryptoAccount:
+            mp_print_str(print, "UR_Value::CryptoAccount");
+            break;
         case Psbt:
             mp_print_str(print, "UR_Value::Psbt");
             break;
@@ -476,6 +479,67 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_KW(mod_foundation_ur_new_derived_key_obj,
                                   1,
                                   mod_foundation_ur_new_derived_key);
 
+/// def new_crypto_account(root_key_data,
+///                        root_chain_code,
+///                        casa_key_data,
+///                        casa_chain_code,
+///                        master_fingerprint,
+///                        network) -> Value:
+///     """
+///     Create Casa's two-key wallet-registration payload.
+///     """
+STATIC mp_obj_t mod_foundation_ur_new_crypto_account(size_t n_args,
+                                                     const mp_obj_t *pos_args,
+                                                     mp_map_t *kw_args)
+{
+    mp_buffer_info_t root_key_data = {0};
+    mp_buffer_info_t root_chain_code = {0};
+    mp_buffer_info_t casa_key_data = {0};
+    mp_buffer_info_t casa_chain_code = {0};
+    UR_Value value = {0};
+
+    static const mp_arg_t allowed_args[] = {
+        { MP_QSTR_root_key_data,      MP_ARG_REQUIRED | MP_ARG_OBJ, {.u_obj = MP_OBJ_NULL} },
+        { MP_QSTR_root_chain_code,    MP_ARG_REQUIRED | MP_ARG_OBJ, {.u_obj = MP_OBJ_NULL} },
+        { MP_QSTR_casa_key_data,      MP_ARG_REQUIRED | MP_ARG_OBJ, {.u_obj = MP_OBJ_NULL} },
+        { MP_QSTR_casa_chain_code,    MP_ARG_REQUIRED | MP_ARG_OBJ, {.u_obj = MP_OBJ_NULL} },
+        { MP_QSTR_master_fingerprint, MP_ARG_REQUIRED | MP_ARG_OBJ, {.u_obj = MP_OBJ_NULL} },
+        { MP_QSTR_network,            MP_ARG_REQUIRED | MP_ARG_OBJ, {.u_obj = MP_OBJ_NULL} },
+    };
+
+    mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
+    mp_arg_parse_all(n_args, pos_args, kw_args,
+                     MP_ARRAY_SIZE(allowed_args), allowed_args, args);
+
+    mp_get_buffer_raise(args[0].u_obj, &root_key_data, MP_BUFFER_READ);
+    mp_get_buffer_raise(args[1].u_obj, &root_chain_code, MP_BUFFER_READ);
+    mp_get_buffer_raise(args[2].u_obj, &casa_key_data, MP_BUFFER_READ);
+    mp_get_buffer_raise(args[3].u_obj, &casa_chain_code, MP_BUFFER_READ);
+
+    if (root_key_data.len != 33 || casa_key_data.len != 33) {
+        mp_raise_msg(&mp_type_ValueError,
+                     MP_ERROR_TEXT("key data should be 33 bytes"));
+    }
+    if (root_chain_code.len != 32 || casa_chain_code.len != 32) {
+        mp_raise_msg(&mp_type_ValueError,
+                     MP_ERROR_TEXT("chain code should be 32 bytes"));
+    }
+
+    ur_registry_new_crypto_account(
+        &value,
+        root_key_data.buf,
+        root_chain_code.buf,
+        casa_key_data.buf,
+        casa_chain_code.buf,
+        mp_obj_int_get_uint_checked(args[4].u_obj),
+        mp_obj_int_get_uint_checked(args[5].u_obj));
+
+    return MP_OBJ_FROM_PTR(mod_foundation_ur_Value_new(&value));
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_KW(mod_foundation_ur_new_crypto_account_obj,
+                                  4,
+                                  mod_foundation_ur_new_crypto_account);
+
 /// def new_psbt(data: bytes) -> Value:
 ///     """
 ///     """
@@ -749,6 +813,7 @@ STATIC const mp_rom_map_elem_t mod_foundation_ur_globals_table[] = {
     {MP_ROM_QSTR(MP_QSTR_new_bytes), MP_ROM_PTR(&mod_foundation_ur_new_bytes_obj)},
     {MP_ROM_QSTR(MP_QSTR_new_raw), MP_ROM_PTR(&mod_foundation_ur_new_raw_obj)},
     {MP_ROM_QSTR(MP_QSTR_new_derived_key), MP_ROM_PTR(&mod_foundation_ur_new_derived_key_obj)},
+    {MP_ROM_QSTR(MP_QSTR_new_crypto_account), MP_ROM_PTR(&mod_foundation_ur_new_crypto_account_obj)},
     {MP_ROM_QSTR(MP_QSTR_new_psbt), MP_ROM_PTR(&mod_foundation_ur_new_psbt_obj)},
     {MP_ROM_QSTR(MP_QSTR_new_passport_response), MP_ROM_PTR(&mod_foundation_ur_new_passport_response_obj)},
 

### ports/stm32/boards/Passport/modules/wallets/casa.py
@@ -34,17 +34,16 @@ def create_casa_export(sw_wallet=None,
             is_mainnet = chain.ctype == 'BTC'
 
             network = ur.NETWORK_MAINNET if is_mainnet else ur.NETWORK_TESTNET
-            use_info = ur.CoinInfo(ur.CoinType.BTC, network)
-            origin = ur.Keypath(source_fingerprint=int(xfp2str(settings.get('xfp')), 16),
-                                depth=0)
-
-            hdkey = ur.new_derived_key(sv.node.public_key(),
-                                       is_private=False,
-                                       chain_code=sv.node.chain_code(),
-                                       use_info=use_info,
-                                       origin=origin)
-
-            return (hdkey, None)
+            casa_node = sv.derive_path("m/45'")
+            account = ur.new_crypto_account(
+                sv.node.public_key(),
+                sv.node.chain_code(),
+                casa_node.public_key(),
+                casa_node.chain_code(),
+                master_fingerprint=int(xfp2str(settings.get('xfp')), 16),
+                network=network)
+
+            return (account, None)
     else:
         with stash.SensitiveValues() as sv:
             s = '''\