diff --git a/net/ipv4/ah4.c b/net/ipv4/ah4.c
new file mode 100644
index 0000000..0e98f22
--- /dev/null
+++ b/net/ipv4/ah4.c
@@ -0,0 +1,335 @@
+#include <linux/config.h>
+#include <linux/module.h>
+#include <net/ip.h>
+#include <net/xfrm.h>
+#include <net/ah.h>
+#include <linux/crypto.h>
+#include <linux/pfkeyv2.h>
+#include <net/icmp.h>
+#include <asm/scatterlist.h>
+
+
+/* Clear mutable options and find final destination to substitute
+ * into IP header for icv calculation. Options are already checked
+ * for validity, so paranoia is not required. */
+
+static int ip_clear_mutable_options(struct iphdr *iph, u32 *daddr)
+{
+	unsigned char * optptr = (unsigned char*)(iph+1);
+	int  l = iph->ihl*4 - sizeof(struct iphdr);
+	int  optlen;
+
+	while (l > 0) {
+		switch (*optptr) {
+		case IPOPT_END:
+			return 0;
+		case IPOPT_NOOP:
+			l--;
+			optptr++;
+			continue;
+		}
+		optlen = optptr[1];
+		if (optlen<2 || optlen>l)
+			return -EINVAL;
+		switch (*optptr) {
+		case IPOPT_SEC:
+		case 0x85:	/* Some "Extended Security" crap. */
+		case 0x86:	/* Another "Commercial Security" crap. */
+		case IPOPT_RA:
+		case 0x80|21:	/* RFC1770 */
+			break;
+		case IPOPT_LSRR:
+		case IPOPT_SSRR:
+			if (optlen < 6)
+				return -EINVAL;
+			memcpy(daddr, optptr+optlen-4, 4);
+			/* Fall through */
+		default:
+			memset(optptr+2, 0, optlen-2);
+		}
+		l -= optlen;
+		optptr += optlen;
+	}
+	return 0;
+}
+
+static int ah_output(struct xfrm_state *x, struct sk_buff *skb)
+{
+	int err;
+	struct iphdr *iph, *top_iph;
+	struct ip_auth_hdr *ah;
+	struct ah_data *ahp;
+	union {
+		struct iphdr	iph;
+		char 		buf[60];
+	} tmp_iph;
+
+	top_iph = skb->nh.iph;
+	iph = &tmp_iph.iph;
+
+	iph->tos = top_iph->tos;
+	iph->ttl = top_iph->ttl;
+	iph->frag_off = top_iph->frag_off;
+
+	if (top_iph->ihl != 5) {
+		iph->daddr = top_iph->daddr;
+		memcpy(iph+1, top_iph+1, top_iph->ihl*4 - sizeof(struct iphdr));
+		err = ip_clear_mutable_options(top_iph, &top_iph->daddr);
+		if (err)
+			goto error;
+	}
+
+	ah = (struct ip_auth_hdr *)((char *)top_iph+top_iph->ihl*4);
+	ah->nexthdr = top_iph->protocol;
+
+	top_iph->tos = 0;
+	top_iph->tot_len = htons(skb->len);
+	top_iph->frag_off = 0;
+	top_iph->ttl = 0;
+	top_iph->protocol = IPPROTO_AH;
+	top_iph->check = 0;
+
+	ahp = x->data;
+	ah->hdrlen  = (XFRM_ALIGN8(sizeof(struct ip_auth_hdr) + 
+				   ahp->icv_trunc_len) >> 2) - 2;
+
+	ah->reserved = 0;
+	ah->spi = x->id.spi;
+	ah->seq_no = htonl(++x->replay.oseq);
+	ahp->icv(ahp, skb, ah->auth_data);
+
+	top_iph->tos = iph->tos;
+	top_iph->ttl = iph->ttl;
+	top_iph->frag_off = iph->frag_off;
+	if (top_iph->ihl != 5) {
+		top_iph->daddr = iph->daddr;
+		memcpy(top_iph+1, iph+1, top_iph->ihl*4 - sizeof(struct iphdr));
+	}
+
+	ip_send_check(top_iph);
+
+	err = 0;
+
+error:
+	return err;
+}
+
+static int ah_input(struct xfrm_state *x, struct xfrm_decap_state *decap, struct sk_buff *skb)
+{
+	int ah_hlen;
+	struct iphdr *iph;
+	struct ip_auth_hdr *ah;
+	struct ah_data *ahp;
+	char work_buf[60];
+
+	if (!pskb_may_pull(skb, sizeof(struct ip_auth_hdr)))
+		goto out;
+
+	ah = (struct ip_auth_hdr*)skb->data;
+	ahp = x->data;
+	ah_hlen = (ah->hdrlen + 2) << 2;
+	
+	if (ah_hlen != XFRM_ALIGN8(sizeof(struct ip_auth_hdr) + ahp->icv_full_len) &&
+	    ah_hlen != XFRM_ALIGN8(sizeof(struct ip_auth_hdr) + ahp->icv_trunc_len)) 
+		goto out;
+
+	if (!pskb_may_pull(skb, ah_hlen))
+		goto out;
+
+	/* We are going to _remove_ AH header to keep sockets happy,
+	 * so... Later this can change. */
+	if (skb_cloned(skb) &&
+	    pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
+		goto out;
+
+	skb->ip_summed = CHECKSUM_NONE;
+
+	ah = (struct ip_auth_hdr*)skb->data;
+	iph = skb->nh.iph;
+
+	memcpy(work_buf, iph, iph->ihl*4);
+
+	iph->ttl = 0;
+	iph->tos = 0;
+	iph->frag_off = 0;
+	iph->check = 0;
+	if (iph->ihl != 5) {
+		u32 dummy;
+		if (ip_clear_mutable_options(iph, &dummy))
+			goto out;
+	}
+        {
+		u8 auth_data[MAX_AH_AUTH_LEN];
+		
+		memcpy(auth_data, ah->auth_data, ahp->icv_trunc_len);
+		skb_push(skb, skb->data - skb->nh.raw);
+		ahp->icv(ahp, skb, ah->auth_data);
+		if (memcmp(ah->auth_data, auth_data, ahp->icv_trunc_len)) {
+			x->stats.integrity_failed++;
+			goto out;
+		}
+	}
+	((struct iphdr*)work_buf)->protocol = ah->nexthdr;
+	skb->nh.raw = skb_pull(skb, ah_hlen);
+	memcpy(skb->nh.raw, work_buf, iph->ihl*4);
+	skb->nh.iph->tot_len = htons(skb->len);
+	skb_pull(skb, skb->nh.iph->ihl*4);
+	skb->h.raw = skb->data;
+
+	return 0;
+
+out:
+	return -EINVAL;
+}
+
+static void ah4_err(struct sk_buff *skb, u32 info)
+{
+	struct iphdr *iph = (struct iphdr*)skb->data;
+	struct ip_auth_hdr *ah = (struct ip_auth_hdr*)(skb->data+(iph->ihl<<2));
+	struct xfrm_state *x;
+
+	if (skb->h.icmph->type != ICMP_DEST_UNREACH ||
+	    skb->h.icmph->code != ICMP_FRAG_NEEDED)
+		return;
+
+	x = xfrm_state_lookup((xfrm_address_t *)&iph->daddr, ah->spi, IPPROTO_AH, AF_INET);
+	if (!x)
+		return;
+	printk(KERN_DEBUG "pmtu discovery on SA AH/%08x/%08x\n",
+	       ntohl(ah->spi), ntohl(iph->daddr));
+	xfrm_state_put(x);
+}
+
+static int ah_init_state(struct xfrm_state *x, void *args)
+{
+	struct ah_data *ahp = NULL;
+	struct xfrm_algo_desc *aalg_desc;
+
+	if (!x->aalg)
+		goto error;
+
+	/* null auth can use a zero length key */
+	if (x->aalg->alg_key_len > 512)
+		goto error;
+
+	if (x->encap)
+		goto error;
+
+	ahp = kmalloc(sizeof(*ahp), GFP_KERNEL);
+	if (ahp == NULL)
+		return -ENOMEM;
+
+	memset(ahp, 0, sizeof(*ahp));
+
+	ahp->key = x->aalg->alg_key;
+	ahp->key_len = (x->aalg->alg_key_len+7)/8;
+	ahp->tfm = crypto_alloc_tfm(x->aalg->alg_name, 0);
+	if (!ahp->tfm)
+		goto error;
+	ahp->icv = ah_hmac_digest;
+	
+	/*
+	 * Lookup the algorithm description maintained by xfrm_algo,
+	 * verify crypto transform properties, and store information
+	 * we need for AH processing.  This lookup cannot fail here
+	 * after a successful crypto_alloc_tfm().
+	 */
+	aalg_desc = xfrm_aalg_get_byname(x->aalg->alg_name, 0);
+	BUG_ON(!aalg_desc);
+
+	if (aalg_desc->uinfo.auth.icv_fullbits/8 !=
+	    crypto_tfm_alg_digestsize(ahp->tfm)) {
+		printk(KERN_INFO "AH: %s digestsize %u != %hu\n",
+		       x->aalg->alg_name, crypto_tfm_alg_digestsize(ahp->tfm),
+		       aalg_desc->uinfo.auth.icv_fullbits/8);
+		goto error;
+	}
+	
+	ahp->icv_full_len = aalg_desc->uinfo.auth.icv_fullbits/8;
+	ahp->icv_trunc_len = aalg_desc->uinfo.auth.icv_truncbits/8;
+	
+	BUG_ON(ahp->icv_trunc_len > MAX_AH_AUTH_LEN);
+	
+	ahp->work_icv = kmalloc(ahp->icv_full_len, GFP_KERNEL);
+	if (!ahp->work_icv)
+		goto error;
+	
+	x->props.header_len = XFRM_ALIGN8(sizeof(struct ip_auth_hdr) + ahp->icv_trunc_len);
+	if (x->props.mode)
+		x->props.header_len += sizeof(struct iphdr);
+	x->data = ahp;
+
+	return 0;
+
+error:
+	if (ahp) {
+		if (ahp->work_icv)
+			kfree(ahp->work_icv);
+		if (ahp->tfm)
+			crypto_free_tfm(ahp->tfm);
+		kfree(ahp);
+	}
+	return -EINVAL;
+}
+
+static void ah_destroy(struct xfrm_state *x)
+{
+	struct ah_data *ahp = x->data;
+
+	if (!ahp)
+		return;
+
+	if (ahp->work_icv) {
+		kfree(ahp->work_icv);
+		ahp->work_icv = NULL;
+	}
+	if (ahp->tfm) {
+		crypto_free_tfm(ahp->tfm);
+		ahp->tfm = NULL;
+	}
+	kfree(ahp);
+}
+
+
+static struct xfrm_type ah_type =
+{
+	.description	= "AH4",
+	.owner		= THIS_MODULE,
+	.proto	     	= IPPROTO_AH,
+	.init_state	= ah_init_state,
+	.destructor	= ah_destroy,
+	.input		= ah_input,
+	.output		= ah_output
+};
+
+static struct net_protocol ah4_protocol = {
+	.handler	=	xfrm4_rcv,
+	.err_handler	=	ah4_err,
+	.no_policy	=	1,
+};
+
+static int __init ah4_init(void)
+{
+	if (xfrm_register_type(&ah_type, AF_INET) < 0) {
+		printk(KERN_INFO "ip ah init: can't add xfrm type\n");
+		return -EAGAIN;
+	}
+	if (inet_add_protocol(&ah4_protocol, IPPROTO_AH) < 0) {
+		printk(KERN_INFO "ip ah init: can't add protocol\n");
+		xfrm_unregister_type(&ah_type, AF_INET);
+		return -EAGAIN;
+	}
+	return 0;
+}
+
+static void __exit ah4_fini(void)
+{
+	if (inet_del_protocol(&ah4_protocol, IPPROTO_AH) < 0)
+		printk(KERN_INFO "ip ah close: can't remove protocol\n");
+	if (xfrm_unregister_type(&ah_type, AF_INET) < 0)
+		printk(KERN_INFO "ip ah close: can't remove xfrm type\n");
+}
+
+module_init(ah4_init);
+module_exit(ah4_fini);
+MODULE_LICENSE("GPL");