from cryptography import x509
from cryptography.hazmat.backends import default_backend
from cryptography.x509.oid import ExtensionOID

# Загрузка сертификата из файла PEM
#with open("certificate.pem", "rb") as cert_file:
#    pem_data = cert_file.read()
#    cert = x509.load_pem_x509_certificate(pem_data, default_backend())

# для DER формата:
with open("certificate.der", "rb") as cert_file:
     der_data = cert_file.read()
     cert = x509.load_der_x509_certificate(der_data, default_backend())

# Проверка наличия расширения Authority Key Identifier
try:
    akid_extension = cert.extensions.get_extension_for_oid(ExtensionOID.AUTHORITY_KEY_IDENTIFIER)
    akid_value = akid_extension.value
    
    # Извлечение key_identifier (обычно это байты в hex формате)
    key_identifier = akid_value.key_identifier
    print("Authority Key Identifier (key_identifier):", key_identifier.hex())
    
    # Дополнительно: можно извлечь authority_cert_issuer и authority_cert_serial_number
    if akid_value.authority_cert_issuer:
        print("Authority Cert Issuer:", akid_value.authority_cert_issuer) 
        
except x509.ExtensionNotFound:
    print("Расширение Authority Key Identifier отсутствует в сертификате.")