diff --git a/include/net/tcp_authopt.h b/include/net/tcp_authopt.h
index 6e9b5ca22f62..9ee5165388b1 100644
--- a/include/net/tcp_authopt.h
+++ b/include/net/tcp_authopt.h
@@ -115,10 +115,17 @@ static inline struct tcp_authopt_key_info *tcp_authopt_select_key(
 int tcp_authopt_hash(
 		char *hash_location,
 		struct tcp_authopt_key_info *key,
 		struct tcp_authopt_info *info,
 		struct sock *sk, struct sk_buff *skb);
+int tcp_v4_authopt_hash_reply(
+		char *hash_location,
+		struct tcp_authopt_info *info,
+		struct tcp_authopt_key_info *key,
+		__be32 saddr,
+		__be32 daddr,
+		struct tcphdr *th);
 int __tcp_authopt_openreq(struct sock *newsk, const struct sock *oldsk, struct request_sock *req);
 static inline int tcp_authopt_openreq(
 		struct sock *newsk,
 		const struct sock *oldsk,
 		struct request_sock *req)
diff --git a/net/ipv4/tcp_authopt.c b/net/ipv4/tcp_authopt.c
index dbe92c87af5a..6803fc39f9b6 100644
--- a/net/ipv4/tcp_authopt.c
+++ b/net/ipv4/tcp_authopt.c
@@ -922,10 +922,72 @@ static int tcp_authopt_get_traffic_key(struct sock *sk,
 out:
 	tcp_authopt_put_kdf_pool(key, pool);
 	return err;
 }
 
+struct tcp_v4_authopt_context_data {
+	__be32 saddr;
+	__be32 daddr;
+	__be16 sport;
+	__be16 dport;
+	__be32 sisn;
+	__be32 disn;
+	__be16 digestbits;
+} __packed;
+
+static int tcp_v4_authopt_get_traffic_key_noskb(struct tcp_authopt_key_info *key,
+						__be32 saddr,
+						__be32 daddr,
+						__be16 sport,
+						__be16 dport,
+						__be32 sisn,
+						__be32 disn,
+						u8 *traffic_key)
+{
+	int err;
+	struct tcp_authopt_alg_pool *pool;
+	struct tcp_v4_authopt_context_data data;
+
+	BUILD_BUG_ON(sizeof(data) != 22);
+
+	pool = tcp_authopt_get_kdf_pool(key);
+	if (IS_ERR(pool))
+		return PTR_ERR(pool);
+
+	err = tcp_authopt_setkey(pool, key);
+	if (err)
+		goto out;
+	err = crypto_ahash_init(pool->req);
+	if (err)
+		goto out;
+
+	// RFC5926 section 3.1.1.1
+	// Separate to keep alignment semi-sane
+	err = crypto_ahash_buf(pool->req, "\x01TCP-AO", 7);
+	if (err)
+		return err;
+	data.saddr = saddr;
+	data.daddr = daddr;
+	data.sport = sport;
+	data.dport = dport;
+	data.sisn = sisn;
+	data.disn = disn;
+	data.digestbits = htons(crypto_ahash_digestsize(pool->tfm) * 8);
+
+	err = crypto_ahash_buf(pool->req, (u8 *)&data, sizeof(data));
+	if (err)
+		goto out;
+	ahash_request_set_crypt(pool->req, NULL, traffic_key, 0);
+	err = crypto_ahash_final(pool->req);
+	if (err)
+		goto out;
+
+out:
+	tcp_authopt_put_kdf_pool(key, pool);
+	return err;
+}
+
 static int crypto_ahash_buf_zero(struct ahash_request *req, int len)
 {
 	u8 zeros[TCP_AUTHOPT_MACLEN] = {0};
 	int buflen, err;
 
@@ -1185,10 +1247,92 @@ int tcp_authopt_hash(char *hash_location,
 	memset(hash_location, 0, TCP_AUTHOPT_MACLEN);
 	return err;
 }
 EXPORT_SYMBOL(tcp_authopt_hash);
 
+/**
+ * tcp_v4_authopt_hash_reply - Hash tcp+ipv4 header without SKB
+ *
+ * @hash_location: output buffer
+ * @info: sending socket's tcp_authopt_info
+ * @key: signing key, from tcp_authopt_select_key.
+ * @saddr: source address
+ * @daddr: destination address
+ * @th: Pointer to TCP header and options
+ */
+int tcp_v4_authopt_hash_reply(char *hash_location,
+			      struct tcp_authopt_info *info,
+			      struct tcp_authopt_key_info *key,
+			      __be32 saddr,
+			      __be32 daddr,
+			      struct tcphdr *th)
+{
+	struct tcp_authopt_alg_pool *pool;
+	u8 macbuf[TCP_AUTHOPT_MAXMACBUF];
+	u8 traffic_key[TCP_AUTHOPT_MAX_TRAFFIC_KEY_LEN];
+	__be32 sne = 0;
+	int err;
+
+	/* Call special code path for computing traffic key without skb
+	 * This can be called from tcp_v4_reqsk_send_ack so caching would be
+	 * difficult here.
+	 */
+	err = tcp_v4_authopt_get_traffic_key_noskb(key, saddr, daddr,
+						   th->source, th->dest,
+						   htonl(info->src_isn), htonl(info->dst_isn),
+						   traffic_key);
+	if (err)
+		goto out_err_traffic_key;
+
+	/* Init mac shash */
+	pool = tcp_authopt_get_mac_pool(key);
+	if (IS_ERR(pool))
+		return PTR_ERR(pool);
+	err = crypto_ahash_setkey(pool->tfm, traffic_key, key->alg->traffic_key_len);
+	if (err)
+		goto out_err;
+	err = crypto_ahash_init(pool->req);
+	if (err)
+		return err;
+
+	err = crypto_ahash_buf(pool->req, (u8 *)&sne, 4);
+	if (err)
+		return err;
+
+	err = tcp_authopt_hash_tcp4_pseudoheader(pool, saddr, daddr, th->doff * 4);
+	if (err)
+		return err;
+
+	// TCP header with checksum set to zero. Caller ensures this.
+	if (WARN_ON_ONCE(th->check != 0))
+		goto out_err;
+	err = crypto_ahash_buf(pool->req, (u8 *)th, sizeof(*th));
+	if (err)
+		goto out_err;
+
+	// TCP options
+	err = tcp_authopt_hash_opts(pool, th, (struct tcphdr_authopt *)(hash_location - 4),
+				    !(key->flags & TCP_AUTHOPT_KEY_EXCLUDE_OPTS));
+	if (err)
+		goto out_err;
+
+	ahash_request_set_crypt(pool->req, NULL, macbuf, 0);
+	err = crypto_ahash_final(pool->req);
+	if (err)
+		goto out_err;
+	memcpy(hash_location, macbuf, TCP_AUTHOPT_MACLEN);
+
+	tcp_authopt_put_mac_pool(key, pool);
+	return 0;
+
+out_err:
+	tcp_authopt_put_mac_pool(key, pool);
+out_err_traffic_key:
+	memset(hash_location, 0, TCP_AUTHOPT_MACLEN);
+	return err;
+}
+
 static struct tcp_authopt_key_info *tcp_authopt_lookup_recv(struct sock *sk,
 							    struct sk_buff *skb,
 							    struct netns_tcp_authopt *net,
 							    int recv_id,
 							    bool *anykey)
