Actually added the sync_key model. Added signature block to the 'get' response

sample. Clarified how the message should be signed.

boards/models/sync_key.py

@@ -0,0 +1,54 b''
+import base64
+from ecdsa import SigningKey, VerifyingKey
+from django.db import models
+
+TYPE_ECDSA = 'ecdsa'
+
+APP_LABEL_BOARDS = 'boards'
+
+
+class KeyPairManager(models.Manager):
+    def generate_key(self, key_type=TYPE_ECDSA):
+        if key_type == TYPE_ECDSA:
+            private = SigningKey.generate()
+            public = private.get_verifying_key()
+
+            private_key_str = private.to_pem().decode()
+            public_key_str = public.to_pem().decode()
+
+            return self.create(public_key=public_key_str,
+                    private_key=private_key_str,
+                    key_type=TYPE_ECDSA)
+        else:
+            return None
+
+    def verify(self, public_key_str, string, signature, key_type=TYPE_ECDSA):
+        if key_type == TYPE_ECDSA:
+            public = VerifyingKey.from_pem(public_key_str)
+            signature_byte = base64.b64decode(signature)
+            try:
+                return public.verify(signature_byte,
+                        string.encode())
+            except BadSignatureError:
+                return False
+        else:
+            return False
+
+
+class KeyPair(models.Model):
+    class Meta:
+        app_label = APP_LABEL_BOARDS
+
+    objects = KeyPairManager()
+
+    public_key = models.TextField()
+    private_key = models.TextField()
+    key_type = models.TextField()
+
+    def __str__(self):
+        return '%s: %s' % (self.key_type, self.public_key)
+
+    def sign(self, string):
+        private = SigningKey.from_pem(self.private_key)
+        signature_byte = private.sign(string.encode())
+        return base64.b64encode(signature_byte)

docs/samples/response_get.xml

@@ -1,8 +1,16 b''
 <?xml version="1.1" encoding="UTF-8" ?>
 <response>
+    <!--
+         Valid statuses are 'success' and 'error'.
+    -->
     <status>success</status>
     <models>
-        <model name="post">
+        <!--
+             ref-id is used only to reference the model block in the
+             signatures block. It could be any string that is unique throughout
+             the file.
+        -->
+        <model name="post" ref-id="1">
             <id key="id1" local-id="1" />
             <title>13</title>
             <text>Thirteen</text>
@@ -23,7 +31,7 b''
                 <id key="id43" local-id="5" />
             </next>
         </model>
-        <model name="post">
+        <model name="post" ref-id="2">
             <id key="id1" local-id="id2" />
             <title>13</title>
             <text>Thirteen</text>
@@ -34,4 +42,15 b''
             </tags>
         </model>
     </models>
+
+    <!-- The signature block is separate from the model block because the
+         signature value should not be included while getting the block sign.
+         When signing a model block, it should be in the canonical XML form.
+         See http://www.w3.org/TR/xml-c14n11/ for details.
+    -->
+    <signatures>
+        <signature model-ref="1" key="id1" value="dhefhtreh" />
+        <signature model-ref="1" key="id45" value="dsgfgdhefhtreh" />
+        <signature model-ref="2" key="id2" value="dehdfh" />
+    </signatures>
 </response>