Name downloaded SSH keys after their actual algorithm

Registration generates ed25519 pairs but the Content-Disposition on the
student key downloads and the `download` attributes in KeyDownloadCard
were hardcoded to `id_rsa`, so users saved ed25519 keys under an RSA
filename. Add `ssh_key_basename()` in `ref.core.util` and a TS twin in
the SPA to pick the name ssh-keygen would default to (id_ed25519 /
id_ecdsa / id_rsa / id_dsa), and route both download endpoints and the
card through it. Also switch admin bootstrap to ed25519 so a freshly
seeded admin user matches the rest of the system.

Author: Nils Bars

spa-frontend/src/components/KeyDownloadCard.vue

@@ -1,5 +1,5 @@
 <script setup lang="ts">
-import { ref } from 'vue';
+import { computed, ref } from 'vue';
 import type { KeyResult } from '../api/registration';
 
 const props = withDefaults(
@@ -10,6 +10,21 @@ const props = withDefaults(
 const pubCopied = ref(false);
 const privCopied = ref(false);
 
+// Pick the filename `ssh-keygen` would default to for this key's algorithm
+// so downloaded files reflect the actual key type (ed25519/ecdsa/rsa/dsa).
+function sshKeyBasename(pubkey: string | null | undefined): string {
+  if (!pubkey) return 'id_rsa';
+  const algo = pubkey.trim().split(/\s+/, 1)[0] ?? '';
+  if (algo === 'ssh-ed25519') return 'id_ed25519';
+  if (algo.startsWith('ecdsa-sha2-')) return 'id_ecdsa';
+  if (algo === 'ssh-dss') return 'id_dsa';
+  return 'id_rsa';
+}
+
+const keyBasename = computed(() => sshKeyBasename(props.result.pubkey));
+const pubkeyFilename = computed(() => `${keyBasename.value}.pub`);
+const privkeyFilename = computed(() => keyBasename.value);
+
 async function copy(text: string | null, flag: 'pub' | 'priv') {
   if (!text) return;
   try {
@@ -93,11 +108,11 @@ const hasPrivkey = !!props.result.privkey;
         <div style="display: flex; gap: 0.5rem; margin-top: 0.5rem">
           <v-btn
             :href="props.result.pubkey_url"
-            download="id_rsa.pub"
+            :download="pubkeyFilename"
             prepend-icon="mdi-download"
             size="small"
           >
-            Download id_rsa.pub
+            Download {{ pubkeyFilename }}
           </v-btn>
           <v-btn
             size="small"
@@ -124,11 +139,11 @@ const hasPrivkey = !!props.result.privkey;
           <v-btn
             v-if="props.result.privkey_url"
             :href="props.result.privkey_url"
-            download="id_rsa"
+            :download="privkeyFilename"
             prepend-icon="mdi-download"
             size="small"
           >
-            Download id_rsa
+            Download {{ privkeyFilename }}
           </v-btn>
           <v-btn
             size="small"

tests/unit/test_util.py

@@ -8,7 +8,12 @@
 from unittest.mock import MagicMock, patch
 from colorama import Fore, Style
 
-from ref.core.util import AnsiColorUtil, is_db_serialization_error, is_deadlock_error
+from ref.core.util import (
+    AnsiColorUtil,
+    is_db_serialization_error,
+    is_deadlock_error,
+    ssh_key_basename,
+)
 
 
 @pytest.mark.offline
@@ -223,3 +228,43 @@ def test_multiline_text(self):
         result = AnsiColorUtil.green(multiline)
         # The entire multiline text should be wrapped, not each line
         assert result == f"{Fore.GREEN}{multiline}{Style.RESET_ALL}"
+
+
+@pytest.mark.offline
+class TestSshKeyBasename:
+    """Filename mapping for OpenSSH public keys."""
+
+    def test_ed25519(self):
+        assert (
+            ssh_key_basename("ssh-ed25519 AAAAC3NzaC1lZDI1NTE5 comment") == "id_ed25519"
+        )
+
+    def test_rsa(self):
+        assert ssh_key_basename("ssh-rsa AAAAB3NzaC1yc2E comment") == "id_rsa"
+
+    def test_ecdsa_nistp256(self):
+        assert (
+            ssh_key_basename("ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTY=")
+            == "id_ecdsa"
+        )
+
+    def test_ecdsa_nistp521(self):
+        assert ssh_key_basename("ecdsa-sha2-nistp521 AAAA") == "id_ecdsa"
+
+    def test_dsa(self):
+        assert ssh_key_basename("ssh-dss AAAAB3NzaC1kc3M=") == "id_dsa"
+
+    def test_none(self):
+        assert ssh_key_basename(None) == "id_rsa"
+
+    def test_empty_string(self):
+        assert ssh_key_basename("") == "id_rsa"
+
+    def test_whitespace_only(self):
+        assert ssh_key_basename("   \n") == "id_rsa"
+
+    def test_leading_whitespace_is_stripped(self):
+        assert ssh_key_basename("   ssh-ed25519 AAAA") == "id_ed25519"
+
+    def test_unknown_algo_falls_back_to_rsa(self):
+        assert ssh_key_basename("bogus-algo AAAA") == "id_rsa"

webapp/ref/__init__.py

@@ -8,6 +8,13 @@
 from types import MethodType
 
 from Crypto.PublicKey import RSA, ECC
+from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey
+from cryptography.hazmat.primitives.serialization import (
+    Encoding,
+    NoEncryption,
+    PrivateFormat,
+    PublicFormat,
+)
 from flask import Blueprint, Flask, current_app, g, render_template, request, url_for
 from flask.logging import default_handler, wsgi_errors_stream
 from flask_limiter import Limiter
@@ -247,9 +254,15 @@ def setup_db_default_data(app: Flask):
                 admin.pub_key = admin.pub_key.decode()
             admin.priv_key = None
         else:
-            key = RSA.generate(2048)
-            admin.pub_key = key.export_key(format="OpenSSH").decode()
-            admin.priv_key = key.export_key().decode()
+            key = Ed25519PrivateKey.generate()
+            admin.pub_key = (
+                key.public_key()
+                .public_bytes(Encoding.OpenSSH, PublicFormat.OpenSSH)
+                .decode()
+            )
+            admin.priv_key = key.private_bytes(
+                Encoding.PEM, PrivateFormat.OpenSSH, NoEncryption()
+            ).decode()
 
         with app.app_context():
             app.db.session.add(admin)

webapp/ref/core/util.py

@@ -22,6 +22,27 @@
 _database_lock = RLock()
 
 
+def ssh_key_basename(pubkey: str | None) -> str:
+    """Return the conventional OpenSSH filename base for a public key line.
+
+    Maps the algorithm identifier in an OpenSSH-format public key (e.g.
+    ``ssh-ed25519 AAAA...``) to the filename ``ssh-keygen`` would pick by
+    default (``id_ed25519``, ``id_rsa``, ``id_ecdsa``, ``id_dsa``). Unknown
+    or missing keys fall back to ``id_rsa`` to preserve historical behaviour.
+    """
+    if not pubkey:
+        return "id_rsa"
+    parts = pubkey.strip().split(None, 1)
+    algo = parts[0] if parts else ""
+    if algo == "ssh-ed25519":
+        return "id_ed25519"
+    if algo.startswith("ecdsa-sha2-"):
+        return "id_ecdsa"
+    if algo == "ssh-dss":
+        return "id_dsa"
+    return "id_rsa"
+
+
 class DatabaseLockTimeoutError(Exception):
     """Raised when waiting for database lock exceeds timeout."""
 

webapp/ref/view/student.py

@@ -31,6 +31,7 @@
 from ref.core.logging import get_logger
 from ref.core.util import (
     redirect_to_next,
+    ssh_key_basename,
 )
 from ref.model import GroupNameList, SystemSettingsManager, User, UserGroup
 from ref.model.enums import UserAuthorizationGroups
@@ -155,10 +156,11 @@ def student_download_pubkey(signed_mat: str):
 
     student = User.query.filter(User.mat_num == mat_num).one_or_none()
     if student:
+        filename = f"{ssh_key_basename(student.pub_key)}.pub"
         return Response(
             student.pub_key,
             mimetype="text/plain",
-            headers={"Content-disposition": "attachment; filename=id_rsa.pub"},
+            headers={"Content-disposition": f"attachment; filename={filename}"},
         )
 
     flash.error("Unknown student")
@@ -185,10 +187,11 @@ def student_download_privkey(signed_mat: str):
 
     student = User.query.filter(User.mat_num == mat_num).one_or_none()
     if student:
+        filename = ssh_key_basename(student.pub_key)
         return Response(
             student.priv_key,
             mimetype="text/plain",
-            headers={"Content-disposition": "attachment; filename=id_rsa"},
+            headers={"Content-disposition": f"attachment; filename={filename}"},
         )
 
     flash.error("Unknown student")