diff --git a/include/net/ah.h b/include/net/ah.h
new file mode 100644
index 0000000..ceff00a
--- /dev/null
+++ b/include/net/ah.h
@@ -0,0 +1,35 @@
+#ifndef _NET_AH_H
+#define _NET_AH_H
+
+#include <net/xfrm.h>
+
+/* This is the maximum truncated ICV length that we know of. */
+#define MAX_AH_AUTH_LEN	12
+
+struct ah_data
+{
+	u8			*key;
+	int			key_len;
+	u8			*work_icv;
+	int			icv_full_len;
+	int			icv_trunc_len;
+
+	void			(*icv)(struct ah_data*,
+	                               struct sk_buff *skb, u8 *icv);
+
+	struct crypto_tfm	*tfm;
+};
+
+static inline void
+ah_hmac_digest(struct ah_data *ahp, struct sk_buff *skb, u8 *auth_data)
+{
+	struct crypto_tfm *tfm = ahp->tfm;
+
+	memset(auth_data, 0, ahp->icv_trunc_len);
+	crypto_hmac_init(tfm, ahp->key, &ahp->key_len);
+	skb_icv_walk(skb, tfm, 0, skb->len, crypto_hmac_update);
+	crypto_hmac_final(tfm, ahp->key, &ahp->key_len, ahp->work_icv);
+	memcpy(auth_data, ahp->work_icv, ahp->icv_trunc_len);
+}
+
+#endif