diff --git a/src/Cookie.php b/src/Cookie.php
index db32c11..cf3816b 100644
--- a/src/Cookie.php
+++ b/src/Cookie.php
@@ -2,10 +2,12 @@
 declare(strict_types=1);
 namespace ParagonIE\Halite;
 
+use ParagonIE\ConstantTime\Base64UrlSafe;
 use ParagonIE\Halite\{
     Alerts\InvalidMessage,
-    Symmetric\EncryptionKey,
-    Symmetric\Crypto
+    Symmetric\Config as SymmetricConfig,
+    Symmetric\Crypto,
+    Symmetric\EncryptionKey
 };
 
 /**
@@ -54,8 +56,13 @@ public function fetch(string $name)
             return null;
         }
         try {
-            $decrypted = Crypto::decrypt($_COOKIE[$name], $this->key)
-                ->getString();
+            $stored = new HiddenString($_COOKIE[$name]);
+            $config = self::getConfig($stored);
+            $decrypted = Crypto::decrypt(
+                $stored,
+                $this->key,
+                $config->ENCODING
+            )->getString();
             if (empty($decrypted)) {
                 return null;
             }
@@ -64,6 +71,33 @@ public function fetch(string $name)
             return null;
         }
     }
+
+    /**
+     * Get the configuration for this version of halite
+     *
+     * @param HiddenString $stored   A stored password hash
+     * @return SymmetricConfig
+     * @throws InvalidMessage
+     */
+    protected static function getConfig(HiddenString $stored): SymmetricConfig
+    {
+        $stored = $stored->getString();
+        $length = Util::safeStrlen($stored);
+        // This doesn't even have a header.
+        if ($length < 8) {
+            throw new InvalidMessage(
+                'Encrypted password hash is way too short.'
+            );
+        }
+        if (\hash_equals(Util::safeSubstr($stored, 0, 5), Halite::VERSION_PREFIX)) {
+            return SymmetricConfig::getConfig(
+                Base64UrlSafe::decode($stored),
+                'encrypt'
+            );
+        }
+        $v = \Sodium\hex2bin(Util::safeSubstr($stored, 0, 8));
+        return SymmetricConfig::getConfig($v, 'encrypt');
+    }
     
     /**
      * Store a value in an encrypted cookie
diff --git a/src/Password.php b/src/Password.php
index e874e95..ca309f5 100644
--- a/src/Password.php
+++ b/src/Password.php
@@ -23,13 +23,13 @@ final class Password
      * Hash then encrypt a password
      *
      * @param HiddenString $password    The user's password
-     * @param EncryptionKey $secret_key The master key for all passwords
+     * @param EncryptionKey $secretKey  The master key for all passwords
      * @param string $level             The security level for this password
      * @return HiddenString             An encrypted hash to store
      */
     public static function hash(
         HiddenString $password,
-        EncryptionKey $secret_key,
+        EncryptionKey $secretKey,
         string $level = KeyFactory::INTERACTIVE
     ): HiddenString {
         $kdfLimits = KeyFactory::getSecurityLevels($level);
@@ -43,7 +43,7 @@ public static function hash(
         // Now let's encrypt the result
         return Crypto::encrypt(
             new HiddenString($hashed),
-            $secret_key
+            $secretKey
         );
     }
 
@@ -51,7 +51,7 @@ public static function hash(
      * Is this password hash stale?
      *
      * @param HiddenString $stored      Encrypted password hash
-     * @param EncryptionKey $secret_key The master key for all passwords
+     * @param EncryptionKey $secretKey  The master key for all passwords
      * @param string $level             The security level for this password
      * @return bool                     Do we need to regenerate the hash or
      *                                  ciphertext?
@@ -59,21 +59,20 @@ public static function hash(
      */
     public static function needsRehash(
         HiddenString $stored,
-        EncryptionKey $secret_key,
+        EncryptionKey $secretKey,
         string $level = KeyFactory::INTERACTIVE
     ): bool {
         $config = self::getConfig($stored);
-        $v = \Sodium\hex2bin(Util::safeSubstr($stored->getString(), 0, 8));
-        if (!\hash_equals(Halite::HALITE_VERSION, $v)) {
-            // Outdated version of the library; Always rehash without decrypting
-            return true;
-        }
         if (Util::safeStrlen($stored->getString()) < ($config->SHORTEST_CIPHERTEXT_LENGTH * 4 / 3)) {
             throw new InvalidMessage('Encrypted password hash is too short.');
         }
 
         // First let's decrypt the hash
-        $hash_str = Crypto::decrypt($stored, $secret_key)->getString();
+        $hash_str = Crypto::decrypt(
+            $stored,
+            $secretKey,
+            $config->ENCODING
+        )->getString();
 
         // Upon successful decryption, verify that we're using Argon2i
         if (!\hash_equals(
@@ -122,7 +121,7 @@ protected static function getConfig(HiddenString $stored): SymmetricConfig
                 'Encrypted password hash is way too short.'
             );
         }
-        if (Util::safeSubstr($stored, 0, 5) === Halite::VERSION_PREFIX) {
+        if (\hash_equals(Util::safeSubstr($stored, 0, 5), Halite::VERSION_PREFIX)) {
             return SymmetricConfig::getConfig(
                 Base64UrlSafe::decode($stored),
                 'encrypt'
@@ -137,14 +136,14 @@ protected static function getConfig(HiddenString $stored): SymmetricConfig
      *
      * @param HiddenString $password    The user's password
      * @param HiddenString $stored      The encrypted password hash
-     * @param EncryptionKey $secret_key The master key for all passwords
+     * @param EncryptionKey $secretKey The master key for all passwords
      * @return bool                     Is this password valid?
      * @throws InvalidMessage
      */
     public static function verify(
         HiddenString $password,
         HiddenString $stored,
-        EncryptionKey $secret_key
+        EncryptionKey $secretKey
     ): bool {
         $config = self::getConfig($stored);
         // Hex-encoded, so the minimum ciphertext length is double:
@@ -152,7 +151,7 @@ public static function verify(
             throw new InvalidMessage('Encrypted password hash is too short.');
         }
         // First let's decrypt the hash
-        $hash_str = Crypto::decrypt($stored, $secret_key);
+        $hash_str = Crypto::decrypt($stored, $secretKey);
         // Upon successful decryption, verify the password is correct
         return \Sodium\crypto_pwhash_str_verify(
             $hash_str->getString(),
diff --git a/src/Symmetric/Config.php b/src/Symmetric/Config.php
index 5c719dc..2d2d30d 100644
--- a/src/Symmetric/Config.php
+++ b/src/Symmetric/Config.php
@@ -68,6 +68,7 @@ public static function getConfigEncrypt(int $major, int $minor): array
                 case 1:
                 case 0:
                     return [
+                        'ENCODING' => Halite::ENCODE_HEX,
                         'SHORTEST_CIPHERTEXT_LENGTH' => 124,
                         'NONCE_BYTES' => \Sodium\CRYPTO_STREAM_NONCEBYTES,
                         'HKDF_SALT_LEN' => 32,
@@ -81,6 +82,7 @@ public static function getConfigEncrypt(int $major, int $minor): array
             switch ($minor) {
                 case 0:
                     return [
+                        'ENCODING' => Halite::ENCODE_BASE64URLSAFE,
                         'SHORTEST_CIPHERTEXT_LENGTH' => 124,
                         'NONCE_BYTES' => \Sodium\CRYPTO_STREAM_NONCEBYTES,
                         'HKDF_SALT_LEN' => 32,
diff --git a/src/Symmetric/Crypto.php b/src/Symmetric/Crypto.php
index 9edc8ec..7a34cd9 100644
--- a/src/Symmetric/Crypto.php
+++ b/src/Symmetric/Crypto.php
@@ -82,7 +82,7 @@ public static function decrypt(
         
         // Split our keys
         list($encKey, $authKey) = self::splitKeys($secretKey, $salt, $config);
-        
+
         // Check the MAC first
         if (!self::verifyMAC(
             $auth,