diff --git a/bip-0375/validator/psbt_bip375.py b/bip-0375/validator/psbt_bip375.py
new file mode 100644
index 00000000..daf36e99
--- /dev/null
+++ b/bip-0375/validator/psbt_bip375.py
@@ -0,0 +1,95 @@
+#!/usr/bin/env python3
+"""
+BIP-375 PSBT map extensions
+
+BIP375PSBTMap (a PSBTMap subclass with BIP-375 field access helpers)
+BIP375PSBT (a PSBT subclass that deserializes into BIP375PSBTMap instances)
+"""
+
+from io import BytesIO
+import struct
+from typing import List, Optional, Tuple
+
+from deps.bitcoin_test.messages import CTransaction, deser_compact_size, from_binary
+from deps.bitcoin_test.psbt import (
+    PSBT,
+    PSBTMap,
+    PSBT_GLOBAL_VERSION,
+    PSBT_GLOBAL_INPUT_COUNT,
+    PSBT_GLOBAL_OUTPUT_COUNT,
+    PSBT_GLOBAL_UNSIGNED_TX,
+)
+
+PSBT_GLOBAL_SP_ECDH_SHARE = 0x07
+PSBT_GLOBAL_SP_DLEQ = 0x08
+
+PSBT_IN_SP_ECDH_SHARE = 0x1D
+PSBT_IN_SP_DLEQ = 0x1E
+
+PSBT_OUT_SP_V0_INFO = 0x09
+PSBT_OUT_SP_V0_LABEL = 0x0A
+
+
+class BIP375PSBTMap(PSBTMap):
+    """PSBTMap with BIP-375 field access helpers"""
+
+    def __getitem__(self, key):
+        return self.map[key]
+
+    def __contains__(self, key):
+        return key in self.map
+
+    def get(self, key, default=None):
+        return self.map.get(key, default)
+
+    def get_all_by_type(self, key_type: int) -> List[Tuple[bytes, bytes]]:
+        """
+        Get all entries with the given key_type
+
+        Returns list of (key_data, value_data) tuples. For single-byte keys (no
+        key_data), key_data is b''.
+        """
+        result = []
+        for key, value_data in self.map.items():
+            if isinstance(key, int) and key == key_type:
+                result.append((b"", value_data))
+            elif isinstance(key, bytes) and len(key) > 0 and key[0] == key_type:
+                result.append((key[1:], value_data))
+        return result
+
+    def get_by_key(self, key_type: int, key_data: bytes) -> Optional[bytes]:
+        """Get value_data for a specific key_type + key_data combination"""
+        if key_data == b"":
+            return self.map.get(key_type)
+        return self.map.get(bytes([key_type]) + key_data)
+
+
+class BIP375PSBT(PSBT):
+    """PSBT that deserializes maps as BIP375PSBTMap instances"""
+
+    def deserialize(self, f):
+        assert f.read(5) == b"psbt\xff"
+        self.g = from_binary(BIP375PSBTMap, f)
+
+        self.version = 0
+        if PSBT_GLOBAL_VERSION in self.g.map:
+            assert PSBT_GLOBAL_INPUT_COUNT in self.g.map
+            assert PSBT_GLOBAL_OUTPUT_COUNT in self.g.map
+            self.version = struct.unpack("<I", self.g.map[PSBT_GLOBAL_VERSION])[0]
+            assert self.version in [0, 2]
+        if self.version == 2:
+            self.in_count = deser_compact_size(
+                BytesIO(self.g.map[PSBT_GLOBAL_INPUT_COUNT])
+            )
+            self.out_count = deser_compact_size(
+                BytesIO(self.g.map[PSBT_GLOBAL_OUTPUT_COUNT])
+            )
+        else:
+            assert PSBT_GLOBAL_UNSIGNED_TX in self.g.map
+            tx = from_binary(CTransaction, self.g.map[PSBT_GLOBAL_UNSIGNED_TX])
+            self.in_count = len(tx.vin)
+            self.out_count = len(tx.vout)
+
+        self.i = [from_binary(BIP375PSBTMap, f) for _ in range(self.in_count)]
+        self.o = [from_binary(BIP375PSBTMap, f) for _ in range(self.out_count)]
+        return self