diff --git a/include/crypto/poly1305.h b/include/crypto/poly1305.h
index 74c6e1c..f1f67fc 100644
--- a/include/crypto/poly1305.h
+++ b/include/crypto/poly1305.h
@@ -13,12 +13,29 @@
 #define POLY1305_KEY_SIZE	32
 #define POLY1305_DIGEST_SIZE	16
 
+/* The poly1305_key and poly1305_state types are mostly opaque and
+ * implementation-defined. Limbs might be in base 2^64 or base 2^26, or
+ * different yet. The union type provided keeps these 64-bit aligned for the
+ * case in which this is implemented using 64x64 multiplies.
+ */
+
 struct poly1305_key {
-	u32 r[5];	/* key, base 2^26 */
+	union {
+		u32 r[5];
+		u64 r64[3];
+	};
+};
+
+struct poly1305_core_key {
+	struct poly1305_key key;
+	struct poly1305_key precomputed_s;
 };
 
 struct poly1305_state {
-	u32 h[5];	/* accumulator, base 2^26 */
+	union {
+		u32 h[5];
+		u64 h64[3];
+	};
 };
 
 struct poly1305_desc_ctx {
@@ -35,7 +52,10 @@
 	/* accumulator */
 	struct poly1305_state h;
 	/* key */
-	struct poly1305_key r[CONFIG_CRYPTO_LIB_POLY1305_RSIZE];
+	union {
+		struct poly1305_key opaque_r[CONFIG_CRYPTO_LIB_POLY1305_RSIZE];
+		struct poly1305_core_key core_r;
+	};
 };
 
 void poly1305_init_arch(struct poly1305_desc_ctx *desc, const u8 *key);