[Composer] Upgrade to phpseclib version 3

- Create custom Key file format for Salmon Magic key
- Remove obsolete pemToME and MEtoPem Crypto methods
- Remove unused newECKeypair Crypto method
- Switch to constant-time Base64 encode/decode in Base64Url Strings methods

src/Protocol/Salmon/Format/Magic.php

@@ -0,0 +1,77 @@
+<?php
+/**
+ * @copyright Copyright (C) 2010-2022, the Friendica project
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ */
+
+namespace Friendica\Protocol\Salmon\Format;
+
+use Friendica\Util\Strings;
+use phpseclib3\Math\BigInteger;
+
+/**
+ * This custom public RSA key format class is meant to be used with the \phpseclib3\Crypto\RSA::addFileFormat method.
+ *
+ * It handles Salmon's specific magic key string starting with "RSA." and which MIME type is application/magic-key or
+ * application/magic-public-key
+ *
+ * @see https://web.archive.org/web/20160506073138/http://salmon-protocol.googlecode.com:80/svn/trunk/draft-panzer-magicsig-01.html#anchor13
+ */
+class Magic
+{
+	public static function load($key, $password = ''): array
+	{
+		if (!is_string($key)) {
+			throw new \UnexpectedValueException('Key should be a string - not a ' . gettype($key));
+		}
+
+		$key_info = explode('.', $key);
+
+		if (count($key_info) !== 3) {
+			throw new \UnexpectedValueException('Key should have three components separated by periods');
+		}
+
+		if ($key_info[0] !== 'RSA') {
+			throw new \UnexpectedValueException('Key first component should be "RSA"');
+		}
+
+		if (preg_match('#[+/]#', $key_info[1])
+			|| preg_match('#[+/]#', $key_info[1])
+		) {
+			throw new \UnexpectedValueException('Wrong encoding, expecting Base64URLencoding');
+		}
+
+		$m = Strings::base64UrlDecode($key_info[1]);
+		$e = Strings::base64UrlDecode($key_info[2]);
+
+		if (!$m || !$e) {
+			throw new \UnexpectedValueException('Base64 decoding produced an error');
+		}
+
+		return [
+			'modulus'        => new BigInteger($m, 256),
+			'publicExponent' => new BigInteger($e, 256),
+			'isPublicKey'    => true,
+		];
+	}
+
+	public static function savePublicKey(BigInteger $n, BigInteger $e, array $options = []): string
+	{
+		return 'RSA.' . Strings::base64UrlEncode($n->toBytes(), true) . '.' . Strings::base64UrlEncode($e->toBytes(), true);
+	}
+}