SFTP: restore the line breaks of an OpenSSH private key before use (#24)

Nextcloud 35 reads keys with phpseclib 3, which refuses an OpenSSH-format
key whose line breaks were lost ("Unable to read key"); phpseclib 2 on
Nextcloud 34 read it. The key is fixed when used, so stored locations work
again without re-entering it.

CHANGELOG.md

@@ -21,6 +21,13 @@ instead carried by the app description, the git tag, the release, and this file.
   expected form (#22). Before, `backup:user:restore <location> <uid>` only said "is not a
   recorded user export for this location".
 
+### Fixed
+- An SFTP location with an RSA key in OpenSSH format ("BEGIN OPENSSH PRIVATE KEY") whose line
+  breaks were lost, e.g. turned into spaces on the way in, stopped working after an upgrade to
+  Nextcloud 35 with "Unable to read key": Nextcloud 35 reads keys with a stricter library. The
+  line breaks are now restored before the key is used, so the stored location works again without
+  re-entering it (#24).
+
 ## [1.0.0-rc.6] - 2026-10-24
 
 Sixth release candidate for 1.0.0; the app version is 0.9.12. Fixes from two disaster recovery

lib/Backend/ExternalStorageFactory.php

@@ -72,6 +72,10 @@ final class ExternalStorageFactory {
 			throw new BackendException("Auth mechanism $authId does not fit backend $backendId");
 		}
 
+		if (is_string($options['private_key'] ?? null)) {
+			$options['private_key'] = self::normalizePrivateKey($options['private_key']);
+		}
+
 		$config = new StorageConfig();
 		$config->setBackend($backend);
 		$config->setAuthMechanism($auth);
@@ -86,4 +90,22 @@ final class ExternalStorageFactory {
 		$storage = $backend->wrapStorage($storage);
 		return $auth->wrapStorage($storage);
 	}
+
+	/**
+	 * An OpenSSH-format private key with its line breaks restored. Up to Nextcloud 34
+	 * (phpseclib 2) a key whose newlines were lost or turned into spaces, e.g. on its way through
+	 * a shell or a form, still loaded; Nextcloud 35 (phpseclib 3) refuses it with "Unable to read
+	 * key" (#24). The key itself is not changed, so it is fixed when it is used, not when stored.
+	 * Other formats (PEM, PKCS#8) still load as they are and are returned unchanged.
+	 */
+	public static function normalizePrivateKey(string $key): string {
+		if (!preg_match('/-----BEGIN OPENSSH PRIVATE KEY-----(.*?)-----END OPENSSH PRIVATE KEY-----/s', $key, $m)) {
+			return $key;
+		}
+		$body = (string)preg_replace('/\s+/', '', $m[1]);
+		if (!preg_match('#^[A-Za-z0-9+/]+=*$#', $body)) {
+			return $key;
+		}
+		return "-----BEGIN OPENSSH PRIVATE KEY-----\n" . chunk_split($body, 70, "\n") . "-----END OPENSSH PRIVATE KEY-----\n";
+	}
 }

tests/Unit/Backend/ExternalStorageFactoryTest.php

@@ -0,0 +1,35 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OCA\NgBackup\Tests\Unit\Backend;
+
+use OCA\NgBackup\Backend\ExternalStorageFactory;
+use PHPUnit\Framework\TestCase;
+
+/** ExternalStorageFactory::normalizePrivateKey(): keys that phpseclib 2 read, for phpseclib 3 (#24). */
+class ExternalStorageFactoryTest extends TestCase {
+	/** An OpenSSH-format key laid out as ssh-keygen writes it; the body is random, not a real key. */
+	private static function key(): string {
+		$body = base64_encode(random_bytes(1000));
+		return "-----BEGIN OPENSSH PRIVATE KEY-----\n" . chunk_split($body, 70, "\n") . "-----END OPENSSH PRIVATE KEY-----\n";
+	}
+
+	public function testRestoresLostLineBreaks(): void {
+		$key = self::key();
+		$this->assertSame($key, ExternalStorageFactory::normalizePrivateKey($key));
+		$this->assertSame($key, ExternalStorageFactory::normalizePrivateKey(str_replace("\n", ' ', $key)), 'newlines as spaces');
+		$this->assertSame($key, ExternalStorageFactory::normalizePrivateKey(str_replace("\n", '', $key)), 'no newlines');
+		$this->assertSame($key, ExternalStorageFactory::normalizePrivateKey(str_replace("\n", "\r\n", $key)), 'CRLF');
+		$this->assertSame($key, ExternalStorageFactory::normalizePrivateKey(rtrim($key)), 'no trailing newline');
+		$this->assertSame($key, ExternalStorageFactory::normalizePrivateKey(preg_replace('/^/m', '  ', $key)), 'indented');
+	}
+
+	public function testLeavesOtherFormatsAlone(): void {
+		$pem = "-----BEGIN RSA PRIVATE KEY-----\nProc-Type: 4,ENCRYPTED\nDEK-Info: DES-EDE3-CBC,FF44E0A94036766C\n\nAAAA\n-----END RSA PRIVATE KEY-----\n";
+		$this->assertSame($pem, ExternalStorageFactory::normalizePrivateKey($pem));
+		$this->assertSame('not a key', ExternalStorageFactory::normalizePrivateKey('not a key'));
+		$odd = "-----BEGIN OPENSSH PRIVATE KEY-----\\nAAAA\\n-----END OPENSSH PRIVATE KEY-----";
+		$this->assertSame($odd, ExternalStorageFactory::normalizePrivateKey($odd), 'not base64 inside: unchanged');
+	}
+}