diff --git a/pyproject.toml b/pyproject.toml
index f1469526..561b5fea 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -19,6 +19,7 @@ dependencies = [
     "cryptography==44.0.0",
     "python-dotenv==1.0.1",
     "requests==2.32.3",
+    "pycryptodome==3.23.0",
     "eth-abi==5.2.0",
 ]
 classifiers = [
diff --git a/src/hiero_sdk_python/crypto/private_key.py b/src/hiero_sdk_python/crypto/private_key.py
index d1124130..2c6c6617 100644
--- a/src/hiero_sdk_python/crypto/private_key.py
+++ b/src/hiero_sdk_python/crypto/private_key.py
@@ -4,7 +4,9 @@
 
 from cryptography.hazmat.primitives import hashes, serialization
 from cryptography.hazmat.primitives.asymmetric import ed25519, ec
+from cryptography.hazmat.primitives.asymmetric import utils as asym_utils
 from hiero_sdk_python.crypto.public_key import PublicKey
+from hiero_sdk_python.utils.crypto_utils import keccak256
 
 class PrivateKey:
     """
@@ -273,8 +275,12 @@ def sign(self, data: bytes) -> bytes:
         if isinstance(self._private_key, ed25519.Ed25519PrivateKey):
             # Ed25519 automatically handles the hashing internally
             return self._private_key.sign(data)
-        # ECDSA requires specifying a hash algorithm
-        return self._private_key.sign(data, ec.ECDSA(hashes.SHA256()))
+        
+        data_hash = keccak256(data)
+        signature_der = self._private_key.sign(data_hash, ec.ECDSA(asym_utils.Prehashed(hashes.SHA256())))
+        r, s = asym_utils.decode_dss_signature(signature_der)
+        signature = r.to_bytes(32, "big") + s.to_bytes(32, "big")
+        return signature
 
     def public_key(self) -> PublicKey:
         """
diff --git a/src/hiero_sdk_python/crypto/public_key.py b/src/hiero_sdk_python/crypto/public_key.py
index 36ab3796..0a45fb0b 100644
--- a/src/hiero_sdk_python/crypto/public_key.py
+++ b/src/hiero_sdk_python/crypto/public_key.py
@@ -4,8 +4,10 @@
 
 from cryptography.hazmat.primitives.asymmetric import ed25519, ec
 from cryptography.hazmat.primitives import serialization, hashes
+from cryptography.hazmat.primitives.asymmetric import utils as asym_utils
 from hiero_sdk_python.hapi.services.basic_types_pb2 import Key
 from hiero_sdk_python.hapi.services import basic_types_pb2
+from hiero_sdk_python.utils.crypto_utils import keccak256
 
 def _warn_ed25519_ambiguity(caller_name: str) -> None:
     warnings.warn(
@@ -485,7 +487,7 @@ def verify_ecdsa(self, signature: bytes, data: bytes) -> None:
         Verify an ECDSA (secp256k1) signature using SHA-256.
 
         Args:
-            signature: The DER-encoded signature bytes.
+            signature: DER-encoded signature bytes, or raw 64-byte signature (r + s concatenated, 32 bytes each)
             data:      The original message bytes.
 
         Raises:
@@ -493,7 +495,17 @@ def verify_ecdsa(self, signature: bytes, data: bytes) -> None:
         """
         if not isinstance(self._public_key, ec.EllipticCurvePublicKey):
             raise TypeError("Not an ECDSA key")
-        self._public_key.verify(signature, data, ec.ECDSA(hashes.SHA256()))
+        
+        # Convert raw 64-byte signature to DER format
+        if len(signature) == 64:
+            r = int.from_bytes(signature[:32], "big")
+            s = int.from_bytes(signature[32:], "big")
+            signature_der = asym_utils.encode_dss_signature(r, s)
+        else:
+            signature_der = signature
+            
+        data_hash = keccak256(data)
+        self._public_key.verify(signature_der, data_hash, ec.ECDSA(asym_utils.Prehashed(hashes.SHA256())))
 
     def __repr__(self) -> str:
         """
diff --git a/src/hiero_sdk_python/transaction/transaction.py b/src/hiero_sdk_python/transaction/transaction.py
index dae1732d..4fbddd7c 100644
--- a/src/hiero_sdk_python/transaction/transaction.py
+++ b/src/hiero_sdk_python/transaction/transaction.py
@@ -164,10 +164,16 @@ def sign(self, private_key):
 
             public_key_bytes = private_key.public_key().to_bytes_raw()
 
-            sig_pair = basic_types_pb2.SignaturePair(
-                pubKeyPrefix=public_key_bytes,
-                ed25519=signature
-            )
+            if private_key.is_ed25519():
+                sig_pair = basic_types_pb2.SignaturePair(
+                    pubKeyPrefix=public_key_bytes,
+                    ed25519=signature
+                )
+            else:
+                sig_pair = basic_types_pb2.SignaturePair(
+                    pubKeyPrefix=public_key_bytes,
+                    ECDSA_secp256k1=signature
+                )
 
             # We initialize the signature map for this body_bytes if it doesn't exist yet
             self._signature_map.setdefault(body_bytes, basic_types_pb2.SignatureMap())
diff --git a/tests/unit/test_keys_public.py b/tests/unit/test_keys_public.py
index 64a1236b..aa312e16 100644
--- a/tests/unit/test_keys_public.py
+++ b/tests/unit/test_keys_public.py
@@ -2,9 +2,11 @@
 import warnings
 from cryptography.hazmat.primitives.asymmetric import ec, ed25519
 from cryptography.hazmat.primitives import serialization, hashes
+from cryptography.hazmat.primitives.asymmetric import utils as asym_utils
 from cryptography.exceptions import InvalidSignature
 from hiero_sdk_python.hapi.services.basic_types_pb2 import Key
 from hiero_sdk_python.crypto.public_key import PublicKey
+from hiero_sdk_python.utils.crypto_utils import keccak256
 
 pytestmark = pytest.mark.unit
 
@@ -529,7 +531,8 @@ def test_verify_ecdsa_success(ecdsa_keypair):
     pk = PublicKey(pub)
 
     msg = b"some message"
-    signature = priv.sign(msg, ec.ECDSA(hashes.SHA256()))
+    msg_hash = keccak256(msg)
+    signature = priv.sign(msg_hash, ec.ECDSA(asym_utils.Prehashed(hashes.SHA256())))
     # If the signature is correct, verify() returns None and raises no error.
     pk.verify(signature, msg)