diff --git a/did.py b/did.py
index fc4fb94..c4512a2 100644
--- a/did.py
+++ b/did.py
@@ -34,7 +34,8 @@ def key_read(path_keys):
 
 
 def get_signing_key(jwk_pr):
-    private_key_material_str = jwk_pr['d']
+    key = json.loads(jwk_pr)
+    private_key_material_str = key['d']
     missing_padding = len(private_key_material_str) % 4
     if missing_padding:
       private_key_material_str += '=' * (4 - missing_padding)
@@ -57,7 +58,8 @@ def generate_keys():
     # Generate an Ed25519 key pair
     key = jwk.JWK.generate(kty='OKP', crv='Ed25519')
     key['kid'] = 'Generated'
-    return key.export_private(True)
+    key_json = key.export_private(True)
+    return json.dumps(key_json)
 
 
 def main():
diff --git a/tests/test_certificate.py b/tests/test_certificate.py
index 8e30bed..3d5eac6 100644
--- a/tests/test_certificate.py
+++ b/tests/test_certificate.py
@@ -13,22 +13,23 @@ from utils import now
 
 def test_generated_did_key():
     key = generate_keys()
+    key_d = json.loads(key)
     did = generate_did(key)
     _did = did.split("#")[0]
     pub = _did.split(":")[-1]
     mc = multiformats.multibase.decode(pub)
     public_key_bytes = multicodec.remove_prefix(mc)
     x = nacl.encoding.URLSafeBase64Encoder.encode(public_key_bytes).decode('utf-8')
-    k_x = key.get('x', '')
+    k_x = key_d.get('x', '')
     missing_padding = len(k_x) % 4
     if missing_padding:
         k_x += '=' * (4 - missing_padding)
 
-    assert key.get('kty') == 'OKP'
-    assert key.get('crv') == 'Ed25519'
-    assert key.get('kid') == 'Generated'
+    assert key_d.get('kty') == 'OKP'
+    assert key_d.get('crv') == 'Ed25519'
+    assert key_d.get('kid') == 'Generated'
     assert k_x == x
-    assert key.get('d') is not None
+    assert key_d.get('d') is not None
 
 
 def test_credential():
@@ -135,6 +136,6 @@ def test_verifiable_presentation():
     holder_did = generate_did(holder_key)
     holder_signing_key = get_signing_key(holder_key)
     vp = sign_vp(holder_signing_key, holder_did, vc_json)
-    verified = verify_vc(json.dumps(vp))
+    verified = verify_vp(json.dumps(vp))
     assert verified