diff --git a/rsa.h b/rsa.h
index 7a129e6..910ae1a 100644
--- a/rsa.h
+++ b/rsa.h
@@ -3,6 +3,9 @@
 #include <stdbool.h>
 #include <stdint.h>
 
+// Common public exponent, in Fermat prime form
+#define PUBEXP ((1 << 16) | 0x1)
+
 /**
  * @brief Calculates greatest common divider of two integers using the euclidean
  * algorithm