drop SESSION-specific stuff and move encrypt/decrypt helpers to a separate class; add a command line flag to generate encryption keys

3 files changed, 70 insertions, 52 deletions

diff --git a/classes/Config.php b/classes/Config.php
index c9acad93e..e906419dc 100644
--- a/classes/Config.php
+++ b/classes/Config.php
@@ -192,8 +192,8 @@ class Config {
 	/** disables login form controls except HOOK_LOGINFORM_ADDITIONAL_BUTTONS (for SSO providers), also prevents logging in through auth_internal */
 	const DISABLE_LOGIN_FORM = "DISABLE_LOGIN_FORM";
 
-	/** optional key to transparently encrypt stored session data using Sodium library (XChaCha20-Poly1305) - generate using bin2hex(sodium_crypto_aead_xchacha20poly1305_ietf_keygen()) */
-	const SESSION_ENCRYPTION_KEY = "SESSION_ENCRYPTION_KEY";
+	/** optional key to transparently encrypt sensitive data (currently limited to sessions); key is a 32 byte hex string may be generated using update.php --gen-encryption-key */
+	const ENCRYPTION_KEY = "ENCRYPTION_KEY";
 
 	/** default values for all global configuration options */
 	private const _DEFAULTS = [
@@ -253,7 +253,7 @@ class Config {
 																					Config::T_STRING ],
 		Config::HTTP_429_THROTTLE_INTERVAL => [ 3600,				Config::T_INT ],
 		Config::DISABLE_LOGIN_FORM => [ "",								Config::T_BOOL ],
-		Config::SESSION_ENCRYPTION_KEY => [ "",                  Config::T_STRING ]
+		Config::ENCRYPTION_KEY => [ "",                  Config::T_STRING ]
 	];
 
 	private static ?Config $instance = null;
diff --git a/classes/Crypt.php b/classes/Crypt.php
new file mode 100644
index 000000000..d832e6530
--- /dev/null
+++ b/classes/Crypt.php
@@ -0,0 +1,62 @@
+<?php
+class Crypt {
+
+   /** the only algo supported at the moment */
+	private const ENCRYPT_ALGO = 'xchacha20poly1305_ietf';
+
+   /** currently only generates keys using sodium_crypto_aead_chacha20poly1305_keygen() i.e. one supported Crypt::ENCRYPT_ALGO
+    * @return string random 256-bit (for ChaCha20-Poly1305) binary string
+   */
+   static function generate_key() : string {
+      return sodium_crypto_aead_chacha20poly1305_keygen();
+   }
+
+	/** encrypts provided ciphertext using Config::ENCRYPTION_KEY into an encrypted object
+	 *
+	 * @return array{'algo': string, 'nonce': string, 'payload': string} encrypted data object containing algo, nonce, and encrypted data
+	*/
+	static function encrypt_string(string $ciphertext) : array {
+		$key = Config::get(Config::ENCRYPTION_KEY);
+
+      if (!$key)
+         throw new Exception("Crypt::encrypt_string() failed to encrypt - key is not available");
+
+		$nonce = \random_bytes(\SODIUM_CRYPTO_AEAD_XCHACHA20POLY1305_IETF_NPUBBYTES);
+
+		$payload = sodium_crypto_aead_xchacha20poly1305_ietf_encrypt($ciphertext, '', $nonce, hex2bin($key));
+
+		if ($payload) {
+			$encrypted_data = [
+				'algo' => self::ENCRYPT_ALGO,
+				'nonce' => $nonce,
+				'payload' => $payload,
+			];
+
+			return $encrypted_data;
+		}
+
+		throw new Exception("Crypt::encrypt_string() failed to encrypt ciphertext");
+	}
+
+	/** decrypts payload of a valid encrypted object using Config::ENCRYPTION_KEY
+	 *
+	 * @param array{'algo': string, 'nonce': string, 'payload': string} $encrypted_data
+	 *
+	 * @return string decrypted string payload
+	 */
+	static function decrypt_string(array $encrypted_data) : string {
+		$key = Config::get(Config::ENCRYPTION_KEY);
+
+      if (!$key)
+         throw new Exception("Crypt::decrypt_string() failed to decrypt - key is not available");
+
+      // only one is supported for the time being
+      switch ($encrypted_data['algo']) {
+         case self::ENCRYPT_ALGO:
+            return sodium_crypto_aead_xchacha20poly1305_ietf_decrypt($encrypted_data['payload'], '', $encrypted_data['nonce'], hex2bin($key));
+      }
+
+      throw new Exception('Crypt::decrypt_string() failed to decrypt passed encrypted data object, unsupported algo: ' . $encrypted_data['algo']);
+	}
+
+}
\ No newline at end of file
diff --git a/classes/Sessions.php b/classes/Sessions.php
index d8f14eed0..f3c0cea42 100644
--- a/classes/Sessions.php
+++ b/classes/Sessions.php
@@ -8,8 +8,6 @@ class Sessions implements \SessionHandlerInterface {
 	private int $session_expire;
 	private string $session_name;
 
-	private const SODIUM_ALGO = 'xchacha20poly1305_ietf';
-
 	public function __construct() {
 		$this->session_expire = min(2147483647 - time() - 1, Config::get(Config::SESSION_COOKIE_LIFETIME));
 		$this->session_name = Config::get(Config::SESSION_NAME);
@@ -55,48 +53,6 @@ class Sessions implements \SessionHandlerInterface {
 		return true;
 	}
 
-	/** encrypts provided ciphertext using Sodium symmetric encryption key if available via Config::SESSION_ENCRYPTION_KEY
-	 *
-	 * @return array<string,mixed> encrypted data object containing algo, nonce, and encrypted data
-	 *
-	*/
-	private function encrypt_string(string $ciphertext) : array {
-		$key = Config::get(Config::SESSION_ENCRYPTION_KEY);
-		$nonce = \random_bytes(\SODIUM_CRYPTO_AEAD_XCHACHA20POLY1305_IETF_NPUBBYTES);
-
-		$payload = sodium_crypto_aead_xchacha20poly1305_ietf_encrypt($ciphertext, '', $nonce, hex2bin($key));
-
-		if ($payload) {
-			$encrypted_data = [
-				'algo' => self::SODIUM_ALGO,
-				'nonce' => $nonce,
-				'payload' => $payload,
-			];
-
-			return $encrypted_data;
-		}
-
-		throw new Exception("Config::encrypt_string() failed to encrypt ciphertext");
-	}
-
-	/** decrypts payload of encrypted object if Config::SESSION_ENCRYPTION_KEY is available and object is in correct format
-	 *
-	 * @param array<string,mixed> $encrypted_data
-	 *
-	 * @return string decrypted string payload
-	 */
-	private function decrypt_string(array $encrypted_data) : string {
-		$key = Config::get(Config::SESSION_ENCRYPTION_KEY);
-
-		if ($encrypted_data['algo'] === self::SODIUM_ALGO) {
-			$payload = sodium_crypto_aead_xchacha20poly1305_ietf_decrypt($encrypted_data['payload'], '', $encrypted_data['nonce'], hex2bin($key));
-
-			return $payload;
-		}
-
-		throw new Exception('Config::decrypt_string() failed to decrypt passed encrypted data');
-	}
-
 	public function read(string $id): false|string {
 		$sth = Db::pdo()->prepare('SELECT data FROM ttrss_sessions WHERE id=?');
 		$sth->execute([$id]);
@@ -104,14 +60,14 @@ class Sessions implements \SessionHandlerInterface {
 		if ($row = $sth->fetch()) {
 			$data = base64_decode($row['data']);
 
-			if (Config::get(Config::SESSION_ENCRYPTION_KEY)) {
+			if (Config::get(Config::ENCRYPTION_KEY)) {
 				$unserialized_data = @unserialize($data); // avoid leaking plaintext session via error message
 
 				if ($unserialized_data !== false)
-					return $this->decrypt_string($unserialized_data);
+					return Crypt::decrypt_string($unserialized_data);
 			}
 
-			// if Sodium key is missing or session data is not in serialized format, return as-is
+			// if encryption key is missing or session data is not in serialized format, assume plaintext data and return as-is
 			return $data;
 		}
 
@@ -124,8 +80,8 @@ class Sessions implements \SessionHandlerInterface {
 
 	public function write(string $id, string $data): bool {
 
-		if (Config::get(Config::SESSION_ENCRYPTION_KEY))
-			$data = serialize($this->encrypt_string($data));
+		if (Config::get(Config::ENCRYPTION_KEY))
+			$data = serialize(Crypt::encrypt_string($data));
 
 		$data = base64_encode($data);