fix: unlock passphrase keys once per connect burst (#1737)

CHANGELOG.md

@@ -13,6 +13,7 @@
 
 - The log line for a rejected proxy login now shows the source address, so you can add it to TRUSTED_PROXY_AUTH_TRUSTED_PROXIES
 - Deleting your own account now removes all of its data, like an admin delete does, instead of leaving some behind
+- An SSH key with a passphrase is unlocked once and kept unlocked in memory for a short time, so connecting to many hosts with it no longer freezes the server for minutes
 
 ## 26.10.5
 

src/backend/tests/utils/ssh-key-utils.test.ts

@@ -11,6 +11,7 @@ import {
   getFriendlyKeyTypeName,
   validateKeyPair,
   isSecurityKeyFile,
+  clearUnlockedKeyCache,
 } from "../../utils/ssh-key-utils.js";
 
 const { parsePrivateKey } = sshpk;
@@ -226,6 +227,32 @@ describe("PKCS#8 runtime key normalization", () => {
   });
 });
 
+describe("encrypted OpenSSH keys", () => {
+  const key = sshpk.generatePrivateKey("ed25519");
+  const encrypted = key.toString("openssh", { passphrase: "pw" }).trim();
+
+  it("unlocks once and hands ssh2 a key that needs no passphrase", () => {
+    clearUnlockedKeyCache();
+    const first = preparePrivateKeyForSSH2(encrypted, "pw");
+    const parsed = ssh2.utils.parseKey(first);
+    expect(parsed).not.toBeInstanceOf(Error);
+    expect(parsePrivateKey(first.toString()).fingerprint().toString()).toBe(
+      key.fingerprint().toString(),
+    );
+    expect(preparePrivateKeyForSSH2(encrypted, "pw").toString()).toBe(
+      first.toString(),
+    );
+  });
+
+  it("leaves the key locked for a wrong or missing passphrase", () => {
+    clearUnlockedKeyCache();
+    expect(preparePrivateKeyForSSH2(encrypted, "wrong").toString()).toBe(
+      encrypted,
+    );
+    expect(preparePrivateKeyForSSH2(encrypted).toString()).toBe(encrypted);
+  });
+});
+
 describe("security key files", () => {
   const str = (v: string | Buffer) => {
     const b = Buffer.from(v);

src/backend/utils/ssh-key-utils.ts

@@ -1,4 +1,4 @@
-import { createPrivateKey } from "node:crypto";
+import { createHash, createPrivateKey } from "node:crypto";
 import sshpk from "sshpk";
 import { getErrorMessage } from "./error-message.js";
 import ssh2Pkg from "ssh2";
@@ -264,12 +264,59 @@ export function isSecurityKeyFile(privateKeyData: string): boolean {
   }
 }
 
+// Unlocking an OpenSSH key runs bcrypt on the main thread (about a second per
+// try), and every connect used to do it 3 or more times. Keep the unlocked copy
+// in memory for a short while so a burst of connects pays for it once.
+const UNLOCKED_KEY_TTL_MS = 15 * 60 * 1000;
+const UNLOCKED_KEY_MAX = 64;
+const unlockedKeys = new Map<string, { text: string; expires: number }>();
+
+function unlockOpenSSHKey(cleanKey: string, passphrase?: string): string {
+  if (
+    !passphrase ||
+    !cleanKey.startsWith("-----BEGIN OPENSSH PRIVATE KEY-----")
+  )
+    return cleanKey;
+  const id = createHash("sha256")
+    .update(cleanKey)
+    .update("\n")
+    .update(passphrase)
+    .digest("hex");
+  const now = Date.now();
+  const hit = unlockedKeys.get(id);
+  if (hit && hit.expires > now) return hit.text;
+  unlockedKeys.delete(id);
+  let text: string;
+  try {
+    text = parsePrivateKey(cleanKey, "openssh", { passphrase }).toString(
+      "openssh",
+    );
+  } catch {
+    // Wrong passphrase or a cipher sshpk lacks; the normal path reports it.
+    return cleanKey;
+  }
+  if (ssh2Utils.parseKey(text) instanceof Error) return cleanKey;
+  if (unlockedKeys.size >= UNLOCKED_KEY_MAX) {
+    const oldest = unlockedKeys.keys().next().value;
+    if (oldest !== undefined) unlockedKeys.delete(oldest);
+  }
+  unlockedKeys.set(id, { text, expires: now + UNLOCKED_KEY_TTL_MS });
+  return text;
+}
+
+export function clearUnlockedKeyCache(): void {
+  unlockedKeys.clear();
+}
+
 export function preparePrivateKeyForSSH2(
   privateKeyData: string,
   passphrase?: string,
 ): Buffer {
   if (isSecurityKeyFile(privateKeyData)) throw new Error(SECURITY_KEY_ERROR);
-  let cleanKey = normalizePrivateKeyText(privateKeyData);
+  let cleanKey = unlockOpenSSHKey(
+    normalizePrivateKeyText(privateKeyData),
+    passphrase,
+  );
   if (
     /^-----BEGIN (?:ENCRYPTED )?PRIVATE KEY-----/.test(cleanKey) &&
     ssh2Utils.parseKey(cleanKey, passphrase) instanceof Error