add subjectkeyidentifier support
diff --git a/docs/x509.rst b/docs/x509.rst
index afc9620..8a85561 100644
--- a/docs/x509.rst
+++ b/docs/x509.rst
@@ -275,6 +275,7 @@
>>> for ext in cert.extensions:
... print(ext)
+ <Extension(oid=<ObjectIdentifier(oid=2.5.29.14, name=subjectKeyIdentifier)>, critical=False, value=<SubjectKeyIdentifier(value=580184241bbc2b52944a3da510721451f5af3ac9)>)>
<Extension(oid=<ObjectIdentifier(oid=2.5.29.19, name=basicConstraints)>, critical=True, value=<BasicConstraints(ca=True, path_length=None)>)>
X.509 CSR (Certificate Signing Request) Object
@@ -576,6 +577,25 @@
purposes indicated in the key usage extension. The object is
iterable to obtain the list of :ref:`extended key usage OIDs <eku_oids>`.
+.. class:: SubjectKeyIdentifier
+
+ .. versionadded:: 0.9
+
+ The subject key identifier extension provides a means of identifying
+ certificates that contain a particular public key.
+
+ .. attribute:: digest
+
+ :type: bytes
+
+ The binary value of the identifier.
+
+ .. attribute:: hexdigest
+
+ :type: :term:`text`
+
+ The hexadecimal value of the identifier.
+
Object Identifiers
~~~~~~~~~~~~~~~~~~