Protect SSH from invalid keys

app/ssh/models.py

-from base64 import b64encode, b64decode
+from base64 import b64encode, b64decode, binascii
 import struct
 import hashlib
 from django.db import models
@@ -20,17 +20,22 @@ class SSHPublicKey(models.Model):
         return f"{self.hostname} ({self.keytype})"
 
     def fingerprint_sha256(self):
-        raw_key = b64decode(self.key)
+        try:
+            raw_key = b64decode(self.key)
+        except (ValueError, binascii.Error) as e:
+            return None
         digest = b64encode(hashlib.sha256(raw_key).digest())
         return digest.decode().replace("=", "")
 
     def fingerprint_md5(self):
-        raw_key = b64decode(self.key)
+        try:
+            raw_key = b64decode(self.key)
+        except (ValueError, binascii.Error) as e:
+            return None
         digest = hashlib.md5(raw_key).hexdigest()
         return ":".join(a + b for a, b in zip(digest[::2], digest[1::2]))
 
     def key_length(self):
-        decoded = b64decode(self.key)
 
         def pop(binary):
             if len(binary) < 4:
@@ -39,6 +44,11 @@ class SSHPublicKey(models.Model):
             content = binary[4:4 + length]
             return content, binary[4 + length:]
 
+        try:
+            decoded = b64decode(self.key)
+        except (ValueError, binascii.Error) as e:
+            return None
+
         algo, decoded = pop(decoded)  
         if algo == b"ssh-rsa":
             e, decoded = pop(decoded)  
@@ -47,7 +57,6 @@ class SSHPublicKey(models.Model):
         elif algo == b"ssh-ed25519":
             a, decoded = pop(decoded)  
             return len(a) * 8
-
         return None
 
     def key_algo(self):

app/ssh/tests.py

 from django.test import TestCase
+from django.urls import reverse
+from django.contrib.auth.models import Group
+from guardian.shortcuts import assign_perm
+from . import models
 
-# Create your tests here.
+class KeyDecodeerror(TestCase):
+    """Check pages load even if the key cannot be decoded"""
+
+    def setUp(self):
+        self.toykey = models.SSHPublicKey.objects.create(
+            hostname="example.com",
+            keytype="",
+            key="no such thing",
+        )
+        any_user = Group.objects.get(name="any-user")
+        assign_perm('view_sshpublickey', any_user, self.toykey)
+
+    def test_detail(self):
+        """Check that the detail page loads successfully"""
+        response = self.client.get(
+            reverse('ssh-detail', args=[self.toykey.pk])
+        )
+        self.assertEqual(response.status_code, 200)
+
+    def test_list(self):
+        """Check that the list page loads successfully"""
+        response = self.client.get(
+            reverse('ssh-list')
+        )
+        self.assertEqual(response.status_code, 200)