fix: RSA from JWK sometimes returns empty Instance (#628)

NReib · web-flow · commit b4c78aa73166 · 2026-03-31T12:28:59.000-07:00
diff --git a/src/JWK.php b/src/JWK.php
@@ -240,6 +240,14 @@ private static function createPemFromModulusAndExponent(
     ): string {
         $mod = JWT::urlsafeB64Decode($n);
         $exp = JWT::urlsafeB64Decode($e);
+        // Correct encoding for ASN1, as ints are represented as unsigned in jwk
+        // but signed in ASN1. Prepending null byte makes it unsigned.
+        if (\strlen($mod) > 0 && \ord($mod[0]) >= 128) {
+            $mod = \chr(0) . $mod;
+        }
+        if (\strlen($exp) > 0 && \ord($exp[0]) >= 128) {
+            $exp = \chr(0) . $exp;
+        }
 
         $modulus = \pack('Ca*a*', 2, self::encodeLength(\strlen($mod)), $mod);
         $publicExponent = \pack('Ca*a*', 2, self::encodeLength(\strlen($exp)), $exp);
