diff --git a/proto/ospf/config.Y b/proto/ospf/config.Y
index c859960f..7b35b191 100644
--- a/proto/ospf/config.Y
+++ b/proto/ospf/config.Y
@@ -42,6 +42,20 @@ ospf_iface_finish(void)
 
   if ((ip->autype == OSPF_AUTH_NONE) && (ip->passwords != NULL))
     log(L_WARN "Password option without authentication option does not make sense");
+
+  if (ip->passwords)
+  {
+    struct password_item *pass;
+    WALK_LIST(pass, *ip->passwords)
+    {
+      if (pass->alg && (ip->autype != OSPF_AUTH_CRYPT))
+	cf_error("Password algorithm option requires cryptographic authentication");
+
+      /* Set default OSPF crypto algorithms */
+      if (!pass->alg && (ip->autype == OSPF_AUTH_CRYPT))
+	pass->alg = ospf_cfg_is_v2() ? ALG_MD5 : ALG_HMAC_SHA256;
+    }
+  }
 }
 
 static void
diff --git a/proto/ospf/iface.c b/proto/ospf/iface.c
index 67ae094d..280fa4c1 100644
--- a/proto/ospf/iface.c
+++ b/proto/ospf/iface.c
@@ -9,6 +9,7 @@
  */
 
 #include "ospf.h"
+#include "nest/password.h"
 
 
 const char *ospf_is_names[] = {
@@ -51,6 +52,18 @@ ifa_tx_length(struct ospf_iface *ifa)
   return ifa->cf->tx_length ?: ifa->iface->mtu;
 }
 
+static inline uint
+ifa_tx_hdrlen(struct ospf_iface *ifa)
+{
+  uint hlen = SIZE_OF_IP_HEADER;
+
+  /* Relevant just for OSPFv2 */
+  if (ifa->autype == OSPF_AUTH_CRYPT)
+    hlen += max_mac_length(ifa->passwords);
+
+  return hlen;
+}
+
 static inline uint
 ifa_bufsize(struct ospf_iface *ifa)
 {
@@ -67,11 +80,7 @@ ifa_flood_queue_size(struct ospf_iface *ifa)
 int
 ospf_iface_assure_bufsize(struct ospf_iface *ifa, uint plen)
 {
-  plen += SIZE_OF_IP_HEADER;
-
-  /* This is relevant just for OSPFv2 */
-  if (ifa->autype == OSPF_AUTH_CRYPT)
-    plen += OSPF_AUTH_CRYPT_SIZE;
+  plen += ifa->tx_hdrlen;
 
   if (plen <= ifa->sk->tbsize)
     return 0;
@@ -574,6 +583,7 @@ ospf_iface_new(struct ospf_area *oa, struct ifa *addr, struct ospf_iface_patt *i
   ifa->stub = ospf_iface_stubby(ip, addr);
   ifa->ioprob = OSPF_I_OK;
   ifa->tx_length = ifa_tx_length(ifa);
+  ifa->tx_hdrlen = ifa_tx_hdrlen(ifa);
   ifa->check_link = ip->check_link;
   ifa->ecmp_weight = ip->ecmp_weight;
   ifa->check_ttl = (ip->ttl_security == 1);
@@ -684,6 +694,7 @@ ospf_iface_new_vlink(struct ospf_proto *p, struct ospf_iface_patt *ip)
   ifa->deadint = ip->deadint;
   ifa->inftransdelay = ip->inftransdelay;
   ifa->tx_length = ospf_is_v2(p) ? IP4_MIN_MTU : IP6_MIN_MTU;
+  ifa->tx_hdrlen = ifa_tx_hdrlen(ifa);
   ifa->autype = ip->autype;
   ifa->passwords = ip->passwords;
   ifa->instance_id = ip->instance_id;
@@ -824,6 +835,9 @@ ospf_iface_reconfigure(struct ospf_iface *ifa, struct ospf_iface_patt *new)
   /* Update passwords */
   ifa->passwords = new->passwords;
 
+  /* Update header length */
+  ifa->tx_hdrlen = ifa_tx_hdrlen(ifa);
+
   /* Remaining options are just for proper interfaces */
   if (ifa->type == OSPF_IT_VLINK)
     return 1;
diff --git a/proto/ospf/ospf.h b/proto/ospf/ospf.h
index ca30e4e0..81c610d5 100644
--- a/proto/ospf/ospf.h
+++ b/proto/ospf/ospf.h
@@ -180,11 +180,7 @@ struct ospf_iface_patt
 
 #define OSPF_RXBUF_MINSIZE 256	/* Minimal allowed size */
   u8 instance_id;
-  u8 autype;			/* Not really used in OSPFv3 */
-#define OSPF_AUTH_NONE 0
-#define OSPF_AUTH_SIMPLE 1
-#define OSPF_AUTH_CRYPT 2
-#define OSPF_AUTH_CRYPT_SIZE 16
+  u8 autype;			/* OSPF_AUTH_*, not really used in OSPFv3 */
   u8 strictnbma;
   u8 check_link;
   u8 ecmp_weight;
@@ -334,6 +330,7 @@ struct ospf_iface
   u8 marked;			/* Used in OSPF reconfigure, 2 for force restart */
   u16 rxbuf;			/* Buffer size */
   u16 tx_length;		/* Soft TX packet length limit, usually MTU */
+  u16 tx_hdrlen;		/* Expected packet header length, less than tx_length */
   u8 check_link;		/* Whether iface link change is used */
   u8 ecmp_weight;		/* Weight used for ECMP */
   u8 link_lsa_suppression;	/* Suppression of Link-LSA origination */
@@ -424,6 +421,11 @@ struct ospf_neighbor
 #define ISM_UNLOOP	5	/* Link up */
 #define ISM_DOWN	6	/* Interface down */
 
+/* OSPF authentication types */
+#define OSPF_AUTH_NONE	0
+#define OSPF_AUTH_SIMPLE 1
+#define OSPF_AUTH_CRYPT	2
+
 
 /* OSPF neighbor states */
 #define NEIGHBOR_DOWN	0
@@ -455,7 +457,6 @@ struct ospf_neighbor
 #define TRANS_WAIT	2	/* Waiting before the end of translation */
 
 
-
 /* Generic option flags */
 #define OPT_V6		0x01	/* OSPFv3, LSA relevant for IPv6 routing calculation */
 #define OPT_E		0x02	/* Related to AS-external LSAs */
@@ -491,7 +492,7 @@ struct ospf_packet
   u8 autype;			/* Undefined for OSPFv3 */
 };
 
-struct ospf_md5
+struct ospf_auth_crypto
 {
   u16 zero;
   u8 keyid;
@@ -502,7 +503,7 @@ struct ospf_md5
 union ospf_auth
 {
   u8 password[8];
-  struct ospf_md5 md5;
+  struct ospf_auth_crypto c32;
 };
 
 /* Packet types */
@@ -896,7 +897,6 @@ void ospf_sh_neigh_info(struct ospf_neighbor *n);
 
 /* packet.c */
 void ospf_pkt_fill_hdr(struct ospf_iface *ifa, void *buf, u8 h_type);
-uint ospf_pkt_maxsize(struct ospf_iface *ifa);
 int ospf_rx_hook(sock * sk, uint size);
 // void ospf_tx_hook(sock * sk);
 void ospf_err_hook(sock * sk, int err);
@@ -905,6 +905,9 @@ void ospf_send_to(struct ospf_iface *ifa, ip_addr ip);
 void ospf_send_to_agt(struct ospf_iface *ifa, u8 state);
 void ospf_send_to_bdr(struct ospf_iface *ifa);
 
+static inline uint ospf_pkt_maxsize(struct ospf_iface *ifa)
+{ return ifa->tx_length - ifa->tx_hdrlen; }
+
 static inline void ospf_send_to_all(struct ospf_iface *ifa)
 { ospf_send_to(ifa, ifa->all_routers); }
 
diff --git a/proto/ospf/packet.c b/proto/ospf/packet.c
index a2fbd089..6b6a97a4 100644
--- a/proto/ospf/packet.c
+++ b/proto/ospf/packet.c
@@ -32,25 +32,12 @@ ospf_pkt_fill_hdr(struct ospf_iface *ifa, void *buf, u8 h_type)
   pkt->autype = ifa->autype;
 }
 
-uint
-ospf_pkt_maxsize(struct ospf_iface *ifa)
-{
-  uint headers = SIZE_OF_IP_HEADER;
-
-  /* Relevant just for OSPFv2 */
-  if (ifa->autype == OSPF_AUTH_CRYPT)
-    headers += OSPF_AUTH_CRYPT_SIZE;
-
-  return ifa->tx_length - headers;
-}
-
 /* We assume OSPFv2 in ospf_pkt_finalize() */
 static void
-ospf_pkt_finalize(struct ospf_iface *ifa, struct ospf_packet *pkt)
+ospf_pkt_finalize(struct ospf_iface *ifa, struct ospf_packet *pkt, uint *plen)
 {
-  struct password_item *passwd = NULL;
+  struct password_item *pass = NULL;
   union ospf_auth *auth = (void *) (pkt + 1);
-  uint plen = ntohs(pkt->length);
 
   pkt->checksum = 0;
   pkt->autype = ifa->autype;
@@ -62,25 +49,25 @@ ospf_pkt_finalize(struct ospf_iface *ifa, struct ospf_packet *pkt)
   switch (ifa->autype)
   {
   case OSPF_AUTH_SIMPLE:
-    passwd = password_find(ifa->passwords, 1);
-    if (!passwd)
+    pass = password_find(ifa->passwords, 1);
+    if (!pass)
     {
       log(L_ERR "No suitable password found for authentication");
       return;
     }
-    strncpy(auth->password, passwd->password, sizeof(auth->password));
+    strncpy(auth->password, pass->password, sizeof(auth->password));
 
   case OSPF_AUTH_NONE:
     {
       void *body = (void *) (auth + 1);
-      uint blen = plen - sizeof(struct ospf_packet) - sizeof(union ospf_auth);
+      uint blen = *plen - sizeof(struct ospf_packet) - sizeof(union ospf_auth);
       pkt->checksum = ipsum_calculate(pkt, sizeof(struct ospf_packet), body, blen, NULL);
     }
     break;
 
   case OSPF_AUTH_CRYPT:
-    passwd = password_find(ifa->passwords, 0);
-    if (!passwd)
+    pass = password_find(ifa->passwords, 0);
+    if (!pass)
     {
       log(L_ERR "No suitable password found for authentication");
       return;
@@ -101,20 +88,25 @@ ospf_pkt_finalize(struct ospf_iface *ifa, struct ospf_packet *pkt)
 
     ifa->csn_use = now;
 
-    auth->md5.zero = 0;
-    auth->md5.keyid = passwd->id;
-    auth->md5.len = OSPF_AUTH_CRYPT_SIZE;
-    auth->md5.csn = htonl(ifa->csn);
+    uint auth_len = mac_type_length(pass->alg);
+    byte *auth_tail = ((byte *) pkt + *plen);
+    *plen += auth_len;
 
-    void *tail = ((void *) pkt) + plen;
-    char password[OSPF_AUTH_CRYPT_SIZE];
-    strncpy(password, passwd->password, sizeof(password));
+    ASSERT(*plen < ifa->sk->tbsize);
 
-    struct hash_context ctx;
-    md5_init(&ctx);
-    md5_update(&ctx, (char *) pkt, plen);
-    md5_update(&ctx, password, OSPF_AUTH_CRYPT_SIZE);
-    memcpy((byte *) tail, md5_final(&ctx), MD5_SIZE);
+    auth->c32.zero = 0;
+    auth->c32.keyid = pass->id;
+    auth->c32.len = auth_len;
+    auth->c32.csn = htonl(ifa->csn);
+
+    /* Append key for keyed hash, append padding for HMAC (RFC 5709 3.3) */
+    if (pass->alg < ALG_HMAC)
+      strncpy(auth_tail, pass->password, auth_len);
+    else
+      memset32(auth_tail, HMAC_MAGIC, auth_len / 4);
+
+    mac_fill(pass->alg, pass->password, pass->length,
+	     (byte *) pkt, *plen, auth_tail);
     break;
 
   default:
@@ -155,13 +147,19 @@ ospf_pkt_checkauth(struct ospf_neighbor *n, struct ospf_iface *ifa, struct ospf_
     return 1;
 
   case OSPF_AUTH_CRYPT:
-    if (auth->md5.len != OSPF_AUTH_CRYPT_SIZE)
-      DROP("invalid MD5 digest length", auth->md5.len);
+    pass = password_find_by_id(ifa->passwords, auth->c32.keyid);
+    if (!pass)
+      DROP("no suitable password found", auth->c32.keyid);
 
-    if (plen + OSPF_AUTH_CRYPT_SIZE > len)
-      DROP("length mismatch", len);
+    uint auth_len = mac_type_length(pass->alg);
 
-    u32 rcv_csn = ntohl(auth->md5.csn);
+    if (plen + auth->c32.len > len)
+      DROP("packet length mismatch", len);
+
+    if (auth->c32.len != auth_len)
+      DROP("wrong authentication length", auth->c32.len);
+
+    u32 rcv_csn = ntohl(auth->c32.csn);
     if (n && (rcv_csn < n->csn))
       // DROP("lower sequence number", rcv_csn);
     {
@@ -172,22 +170,19 @@ ospf_pkt_checkauth(struct ospf_neighbor *n, struct ospf_iface *ifa, struct ospf_
       return 0;
     }
 
-    pass = password_find_by_id(ifa->passwords, auth->md5.keyid);
-    if (!pass)
-      DROP("no suitable password found", auth->md5.keyid);
+    byte *auth_tail = ((byte *) pkt) + plen;
+    byte *auth_data = alloca(auth_len);
+    memcpy(auth_data, auth_tail, auth_len);
 
-    byte *tail = ((byte *) pkt) + plen;
-    char received[OSPF_AUTH_CRYPT_SIZE];
-    memcpy(received, tail, OSPF_AUTH_CRYPT_SIZE);
-    strncpy(tail, pass->password, OSPF_AUTH_CRYPT_SIZE);
+    /* Append key for keyed hash, append padding for HMAC (RFC 5709 3.3) */
+    if (pass->alg < ALG_HMAC)
+      strncpy(auth_tail, pass->password, auth_len);
+    else
+      memset32(auth_tail, HMAC_MAGIC, auth_len / 4);
 
-    struct hash_context ctx;
-    md5_init(&ctx);
-    md5_update(&ctx, (byte *) pkt, plen + OSPF_AUTH_CRYPT_SIZE);
-    char *computed = md5_final(&ctx);
-
-    if (memcmp(received, computed, OSPF_AUTH_CRYPT_SIZE))
-      DROP("wrong MD5 digest", pass->id);
+    if (!mac_verify(pass->alg, pass->password, pass->length,
+		    (byte *) pkt, plen + auth_len, auth_data))
+      DROP("wrong authentication code", pass->id);
 
     if (n)
       n->csn = rcv_csn;
@@ -473,15 +468,10 @@ ospf_send_to(struct ospf_iface *ifa, ip_addr dst)
 {
   sock *sk = ifa->sk;
   struct ospf_packet *pkt = (struct ospf_packet *) sk->tbuf;
-  int plen = ntohs(pkt->length);
+  uint plen = ntohs(pkt->length);
 
   if (ospf_is_v2(ifa->oa->po))
-  {
-    if (ifa->autype == OSPF_AUTH_CRYPT)
-      plen += OSPF_AUTH_CRYPT_SIZE;
-
-    ospf_pkt_finalize(ifa, pkt);
-  }
+    ospf_pkt_finalize(ifa, pkt, &plen);
 
   int done = sk_send_to(sk, plen, dst, 0);
   if (!done)