diff --git a/node/ECC.cpp b/node/ECC.cpp
index 314cec318..b1511fdfc 100644
--- a/node/ECC.cpp
+++ b/node/ECC.cpp
@@ -8,15 +8,10 @@ Derived from public domain code by D. J. Bernstein.
 // This code remains in the public domain.
 
 #include <stdint.h>
-#include <stdlib.h>
 #include <string.h>
 
-#include "Constants.hpp"
 #include "ECC.hpp"
 #include "SHA512.hpp"
-#include "Buffer.hpp"
-#include "Hashtable.hpp"
-#include "Mutex.hpp"
 
 #ifdef __WINDOWS__
 #pragma warning(disable: 4146)
diff --git a/node/ECC.hpp b/node/ECC.hpp
index 9e3fc0b94..6fd21a5ea 100644
--- a/node/ECC.hpp
+++ b/node/ECC.hpp
@@ -11,11 +11,45 @@
  */
 /****/
 
+/*
+ * This file defines the elliptic curve crypto used for ZeroTier V1. The normal
+ * public version uses C25519 and Ed25519, while the FIPS version uses NIST.
+ * FIPS builds are completely incompatible with regular ZeroTier, but that's
+ * fine since FIPS users typically want a fully isolated private network. If you
+ * are not such a user you probably don't want this.
+ */
+
 #ifndef ZT_ECC_HPP
 #define ZT_ECC_HPP
 
 #include "Utils.hpp"
 
+#ifdef ZT_FIPS
+
+/* FIPS140/NIST ECC cryptography */
+/* Note that to be FIPS we also need to link against a FIPS-certified library. */
+
+#include <openssl/evp.h>
+#include <openssl/ec.h>
+#include <openssl/err.h>
+#include <openssl/pem.h>
+#include <openssl/bn.h>
+
+#define ZT_ECC_PUBLIC_KEY_SET_LEN (97 * 2) /* Two ECC P-384 keys */
+#define ZT_ECC_PRIVATE_KEY_SET_LEN (48 * 2) /* Two ECC P-384 secret keys */
+#define ZT_ECC_SIGNATURE_LEN 96 /* NIST P-384 ECDSA signature */
+
+class ECC
+{
+public:
+    struct Public { uint8_t data[ZT_ECC_PUBLIC_KEY_SET_LEN]; };
+	struct Private { uint8_t data[ZT_ECC_PRIVATE_KEY_SET_LEN]; };
+	struct Signature { uint8_t data[ZT_ECC_SIGNATURE_LEN]; };
+	struct Pair { Public pub; Private priv; };
+};
+
+#else // Curve25519 / Ed25519
+
 namespace ZeroTier {
 
 #define ZT_ECC_PUBLIC_KEY_SET_LEN 64
@@ -166,3 +200,5 @@ class ECC
 } // namespace ZeroTier
 
 #endif
+
+#endif