docs: add certificate verification section to README and rename doc file

- Add certificate chain and hash verification section to README
- Rename certificate_chain_verification.md to CERTIFICATE-CHAIN-VERIFICATION.md for consistency
- Move cryptography imports to top of mso/verifier.py per maintainer feedback

Author: FlavPMU

README.md

@@ -183,6 +183,26 @@ mdoc.disclosure_map
 >> ... dictionary containing all the disclosed attributes ...
 ````
 
+### Verify with Certificate Chain and Element Hashes
+
+For production use, verify both the X.509 certificate chain and element hashes:
+
+````python
+from pymdoccbor.mdoc.verifier import MdocCbor
+from cryptography import x509
+from cryptography.hazmat.backends import default_backend
+
+# Load trusted root certificates
+with open('iaca_cert.pem', 'rb') as f:
+    iaca_cert = x509.load_pem_x509_certificate(f.read(), default_backend())
+
+mdoc = MdocCbor()
+mdoc.loads(device_response_bytes)
+is_valid = mdoc.verify(trusted_root_certs=[iaca_cert], verify_hashes=True)
+````
+
+For complete documentation on certificate chain verification and hash verification, see [docs/CERTIFICATE-CHAIN-VERIFICATION.md](docs/CERTIFICATE-CHAIN-VERIFICATION.md).
+
 ### Verify the Mobile Security Object
 
 ````

docs/certificate_chain_verification.md docs/CERTIFICATE-CHAIN-VERIFICATION.mddocs/certificate_chain_verification.md renamed to docs/CERTIFICATE-CHAIN-VERIFICATION.md

@@ -11,6 +11,11 @@
     MsoX509ChainNotFound,
     UnsupportedMsoDataFormat
 )
+
+from cryptography import x509
+from cryptography.hazmat.primitives import hashes
+from cryptography.exceptions import InvalidSignature
+
 from pymdoccbor import settings
 from pymdoccbor.tools import bytes2CoseSign1, cborlist2CoseSign1
 
@@ -132,9 +137,7 @@ def attest_public_key(self, trusted_root_certs: list = None):
             return None
 
         # Verify certificate chain
-        from cryptography import x509
-        from cryptography.hazmat.primitives import hashes
-        from cryptography.exceptions import InvalidSignature
+
 
         # Load DS certificate (first in chain)
         ds_cert = self.x509_certificates[0] if self.x509_certificates else None