Implement HMAC authentication.

Known issues:

  - we create a neighbour entry before the first successful challenge;
  - we compute HMAC for each HMAC TLV rather than just once;
  - we only support sending one HMAC TLV;
  - we don't support key rotation.
Co-authored-by: Clara Do <clarado_perso@yahoo.fr>
Co-authored-by: Weronika Kolodziejak <weronika.kolodziejak@gmail.com>

Makefile

@@ -11,11 +11,13 @@ LDLIBS = -lrt
 
 SRCS = babeld.c net.c kernel.c util.c interface.c source.c neighbour.c \
        route.c xroute.c message.c resend.c configuration.c local.c \
-       disambiguation.c rule.c rfc6234/sha224-256.c BLAKE2/ref/blake2s-ref.c
+       disambiguation.c rule.c hmac.c \
+       rfc6234/sha224-256.c BLAKE2/ref/blake2s-ref.c
 
 OBJS = babeld.o net.o kernel.o util.o interface.o source.o neighbour.o \
        route.o xroute.o message.o resend.o configuration.o local.o \
-       disambiguation.o rule.o rfc6234/sha224-256.o BLAKE2/ref/blake2s-ref.o
+       disambiguation.o rule.o hmac.o \
+       rfc6234/sha224-256.o BLAKE2/ref/blake2s-ref.o
 
 babeld: $(OBJS)
 	$(CC) $(CFLAGS) $(LDFLAGS) -o babeld $(OBJS) $(LDLIBS)

babeld.c

@@ -661,9 +661,10 @@ main(int argc, char **argv)
         }
 
         if(FD_ISSET(protocol_socket, &readfds)) {
+	    unsigned char to[16];
             rc = babel_recv(protocol_socket,
                             receive_buffer, receive_buffer_size,
-                            (struct sockaddr*)&sin6, sizeof(sin6));
+                            (struct sockaddr*)&sin6, sizeof(sin6), to);
             if(rc < 0) {
                 if(errno != EAGAIN && errno != EINTR) {
                     perror("recv");
@@ -675,7 +676,7 @@ main(int argc, char **argv)
                         continue;
                     if(ifp->ifindex == sin6.sin6_scope_id) {
                         parse_packet((unsigned char*)&sin6.sin6_addr, ifp,
-                                     receive_buffer, rc);
+                                     receive_buffer, rc, to);
                         VALGRIND_MAKE_MEM_UNDEFINED(receive_buffer,
                                                     receive_buffer_size);
                         break;

configuration.c

@@ -39,6 +39,7 @@ THE SOFTWARE.
 #include "interface.h"
 #include "route.h"
 #include "kernel.h"
+#include "hmac.h"
 #include "configuration.h"
 #include "rule.h"
 
@@ -322,6 +323,35 @@ get_interface_type(int c, int *type_r, gnc_t gnc, void *closure)
     return c;
 }
 
+static int
+gethex(int c, unsigned char **value_r, int *len_r, gnc_t gnc, void *closure)
+{
+    char *t;
+    unsigned char *value;
+    int len, rc;
+    c = getword(c, &t, gnc, closure);
+    if(c < -1)
+        return c;
+    len = strlen(t);
+    if(len % 2 != 0) {
+	free(t);
+	return -2;
+    }
+    value = malloc(len / 2);
+    if(value == NULL)
+        return -2;
+
+    rc = fromhex(value, t, len);
+    free(t);
+    if(rc < 0) {
+	free(value);
+	return -2;
+    }
+    *value_r = value;
+    *len_r = len / 2;
+    return c;
+}
+
 static void
 free_filter(struct filter *f)
 {
@@ -647,6 +677,17 @@ parse_anonymous_ifconf(int c, gnc_t gnc, void *closure,
             if(c < -1 || penalty <= 0 || penalty > 0xFFFF)
                 goto error;
             if_conf->max_rtt_penalty = penalty;
+        } else if(strcmp(token, "hmac") == 0) {
+	    char *key_id;
+	    struct key *key;
+	    c = getword(c, &key_id, gnc, closure);
+	    if(c < -1) {
+                free(key_id);
+                goto error;
+            }
+	    key = find_key(key_id);
+            if_conf->key = key;
+            free(key_id);
 	} else {
             goto error;
         }
@@ -691,6 +732,65 @@ parse_ifconf(int c, gnc_t gnc, void *closure,
     return -2;
 }
 
+static int
+parse_key(int c, gnc_t gnc, void *closure, struct key **key_return)
+{
+    char *token = NULL;
+    struct key *key;
+
+    key = calloc(1, sizeof(struct key));
+    if(key == NULL)
+	goto error;
+    while(1) {
+	c = skip_whitespace(c, gnc, closure);
+	if(c < 0 || c == '\n' || c == '#') {
+	    c = skip_to_eol(c, gnc, closure);
+	    break;
+	}
+	c = getword(c, &token, gnc, closure);
+	if(c < -1) {
+	    goto error;
+	}
+	if(strcmp(token, "id") == 0) {
+	    c = getword(c, &key->id, gnc, closure);
+	    if(c < -1 || key->id == NULL) {
+		goto error;
+	    }
+	} else if(strcmp(token, "type") == 0) {
+	    char *auth_type;
+	    c = getword(c, &auth_type, gnc, closure);
+	    if(c < -1 || auth_type == NULL)
+		goto error;
+	    if(strcmp(auth_type, "none") == 0) {
+		key->type = AUTH_TYPE_NONE;
+	    } else if(strcmp(auth_type, "sha256") == 0) {
+		key->type = AUTH_TYPE_SHA256;
+	    } else if(strcmp(auth_type, "blake2s") == 0) {
+		key->type = AUTH_TYPE_BLAKE2S;
+	    } else {
+		key->type = 0;
+		free(auth_type);
+		goto error;
+	    }
+	    free(auth_type);
+	} else if(strcmp(token, "value") == 0) {
+	    c = gethex(c, &key->value, &key->len, gnc, closure);
+	    if(c < -1 || key->value == NULL)
+		goto error;
+	} else {
+	    goto error;
+	}
+	free(token);
+    }
+    *key_return = key;
+    return c;
+
+ error:
+    free(token);
+    free(key);
+    return -2;
+}
+
 static void
 add_filter(struct filter *filter, struct filter **filters)
 {
@@ -736,6 +836,7 @@ merge_ifconf(struct interface_conf *dest,
     MERGE(rtt_min);
     MERGE(rtt_max);
     MERGE(max_rtt_penalty);
+    MERGE(key);
 
 #undef MERGE
 }
@@ -1100,6 +1201,32 @@ parse_config_line(int c, gnc_t gnc, void *closure,
         if(c < -1 || !action_return)
             goto fail;
         reopen_logfile();
+    } else if(strcmp(token, "key") == 0) {
+	struct key *key = NULL;
+	c = parse_key(c, gnc, closure, &key);
+	if(c < -1)
+	    goto fail;
+        if(key->id == NULL)
+            goto fail;
+        switch(key->type) {
+        case AUTH_TYPE_SHA256:
+            if(key->len != 32) {
+                free(key);
+                goto fail;
+            }
+            break;
+        case AUTH_TYPE_BLAKE2S:
+            if(key->len != 16) {
+                free(key);
+                goto fail;
+            }
+            break;
+        default:
+            free(key);
+            goto fail;
+        }
+        add_key(key->id, key->type, key->len, key->value);
+        free(key);
     } else {
         c = parse_option(c, gnc, closure, token);
         if(c < -1)

configuration.h

@@ -29,6 +29,10 @@ THE SOFTWARE.
 #define CONFIG_ACTION_UNMONITOR 4
 #define CONFIG_ACTION_NO 5
 
+#define AUTH_TYPE_NONE 0
+#define AUTH_TYPE_SHA256 1
+#define AUTH_TYPE_BLAKE2S 2
+
 struct filter_result {
     unsigned int add_metric; /* allow = 0, deny = INF, metric = <0..INF> */
     unsigned char *src_prefix;

hmac.c

+/*
+Copyright (c) 2018 by Clara Dô and Weronika Kolodziejak
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+*/
+
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+#include <assert.h>
+#include <netinet/in.h>
+
+#include "rfc6234/sha.h"
+#include "BLAKE2/ref/blake2.h"
+
+#include "babeld.h"
+#include "interface.h"
+#include "neighbour.h"
+#include "util.h"
+#include "hmac.h"
+#include "configuration.h"
+#include "message.h"
+
+struct key **keys = NULL;
+int numkeys = 0, maxkeys = 0;
+
+struct key *
+find_key(const char *id)
+{
+    int i;
+    for(i = 0; i < numkeys; i++) {
+        if(strcmp(keys[i]->id, id) == 0)
+            return retain_key(keys[i]);
+    }
+    return NULL;
+}
+
+struct key *
+retain_key(struct key *key)
+{
+    assert(key->ref_count < 0xffff);
+    key->ref_count++;
+    return key;
+}
+
+void
+release_key(struct key *key)
+{
+    assert(key->ref_count > 0);
+    key->ref_count--;
+}
+
+struct key *
+add_key(char *id, int type, int len, unsigned char *value)
+{
+    struct key *key;
+
+    assert(value != NULL && type != 0);
+
+    key = find_key(id);
+    if(key) {
+        key->type = type;
+        key->len = len;
+        key->value = value;
+        return key;
+    }
+
+    if(type == AUTH_TYPE_NONE)
+        return NULL;
+    if(numkeys >= maxkeys) {
+        struct key **new_keys;
+        int n = maxkeys < 1 ? 8 : 2 * maxkeys;
+        new_keys = realloc(keys, n * sizeof(struct key*));
+        if(new_keys == NULL)
+            return NULL;
+        maxkeys = n;
+        keys = new_keys;
+    }
+
+    key = calloc(1, sizeof(struct key));
+    if(key == NULL)
+        return NULL;
+    key->id = id;
+    key->type = type;
+    key->len = len;
+    key->value = value;
+
+    keys[numkeys++] = key;
+    return key;
+}
+
+static int
+compute_hmac(const unsigned char *src, const unsigned char *dst,
+	     const unsigned char *packet_header,
+             const unsigned char *body, int bodylen, struct key *key,
+             unsigned char *hmac_return)
+{
+    unsigned char port[2];
+    int rc;
+
+    DO_HTONS(port, (unsigned short)protocol_port);
+    switch(key->type) {
+    case 1: {
+        SHA256Context inner, outer;
+        unsigned char ipad[64], ihash[32], opad[64];
+        if(key->len != 32)
+            return -1;
+        for(int i = 0; i < 32; i++)
+            ipad[i] = key->value[i] ^ 0x36;
+        for(int i = 32; i < 64; i++)
+            ipad[i] = 0x36;
+        rc = SHA256Reset(&inner);
+        if(rc < 0)
+            return -1;
+        rc = SHA256Input(&inner, ipad, 64);
+        if(rc < 0)
+            return -1;
+
+        rc = SHA256Input(&inner, dst, 16);
+        if(rc != 0)
+            return -1;
+        rc = SHA256Input(&inner, port, 2);
+        if(rc != 0)
+            return -1;
+        rc = SHA256Input(&inner, src, 16);
+        if(rc != 0)
+            return -1;
+        rc = SHA256Input(&inner, port, 2);
+        if(rc != 0)
+            return -1;
+        rc = SHA256Input(&inner, packet_header, 4);
+        if(rc != 0)
+            return -1;
+        rc = SHA256Input(&inner, body, bodylen);
+        if(rc != 0)
+            return -1;
+
+        rc = SHA256Result(&inner, ihash);
+        if(rc != 0)
+            return -1;
+
+        for(int i = 0; i < 32; i++)
+            opad[i] = ihash[i] ^ 0x5c;
+        for(int i = 32; i < 64; i++)
+            opad[i] = 0x5c;
+
+        rc = SHA256Reset(&outer);
+        if(rc != 0)
+            return -1;
+        rc = SHA256Input(&outer, opad, 64);
+        if(rc != 0)
+            return -1;
+        rc = SHA256Input(&outer, ihash, 32);
+        if(rc != 0)
+            return -1;
+        rc = SHA256Result(&outer, hmac_return);
+        if(rc < 0)
+            return -1;
+	return 32;
+    }
+    case 2: {
+        blake2s_state s;
+        if(key->len != 16)
+            return -1;
+        rc = blake2s_init_key(&s, 16, key->value, key->len);
+        if(rc < 0)
+            return -1;
+        rc = blake2s_update(&s, dst, 16);
+        if(rc < 0)
+            return -1;
+        rc = blake2s_update(&s, port, 2);
+        if(rc < 0)
+            return -1;
+        rc = blake2s_update(&s, src, 16);
+        if(rc < 0)
+            return -1;
+        rc = blake2s_update(&s, port, 2);
+        if(rc < 0)
+            return -1;
+        rc = blake2s_update(&s, packet_header, 4);
+        if(rc < 0)
+            return -1;
+        rc = blake2s_update(&s, body, bodylen);
+        if(rc < 0)
+            return -1;
+        rc = blake2s_final(&s, hmac_return, 16);
+        if(rc < 0)
+            return -1;
+
+	return 16;
+    }
+    default:
+        return -1;
+    }
+}
+
+int
+add_hmac(struct buffered *buf, struct interface *ifp,
+         unsigned char *packet_header)
+{
+    int hmaclen;
+    int i = buf->len;
+    unsigned char *dst = buf->sin6.sin6_addr.s6_addr;
+    unsigned char *src;
+
+    if(ifp->numll < 1) {
+        fprintf(stderr, "add_hmac: no link-local address.\n");
+        return -1;
+    }
+    src = ifp->ll[0];
+
+    if(buf->len + 2 + DIGEST_LEN > buf->size) {
+        fprintf(stderr, "Buffer overflow in add_hmac.\n");
+        return -1;
+    }
+
+    hmaclen = compute_hmac(src, dst, packet_header,
+                           buf->buf, buf->len, ifp->key,
+                           buf->buf + i + 2);
+    if(hmaclen < 0)
+        return -1;
+    buf->buf[i++] = MESSAGE_HMAC;
+    buf->buf[i++] = hmaclen;
+    i += hmaclen;
+    return i;
+}
+
+
+static int
+compare_hmac(const unsigned char *src, const unsigned char *dst,
+	     const unsigned char *packet, int bodylen,
+	     const unsigned char *hmac, int hmaclen)
+{
+    unsigned char true_hmac[DIGEST_LEN];
+    int true_hmaclen;
+    int i;
+    for(i = 0; i < numkeys; i++) {
+	true_hmaclen = compute_hmac(src, dst, packet,
+				    packet + 4, bodylen, keys[i],
+                                    true_hmac);
+	if(true_hmaclen != hmaclen) {
+            debugf("Bad hmac length (%d != %d).\n", true_hmaclen, hmaclen);
+	    return -1;
+	}
+	if(memcmp(true_hmac, hmac, hmaclen) == 0)
+            return 1;
+    }
+    return 0;
+}
+
+int
+check_hmac(const unsigned char *packet, int packetlen, int bodylen,
+	   const unsigned char *src, const unsigned char *dst)
+{
+    int i = bodylen + 4;
+    int len;
+
+    debugf("check_hmac %s -> %s\n",
+	   format_address(src), format_address(dst));
+    while(i < packetlen) {
+	if(i + 1 > packetlen) {
+            fprintf(stderr, "Received truncated message.\n");
+            break;
+        }
+        len = packet[i+1];
+        if(packet[i] == MESSAGE_HMAC) {
+	    if(i + len > packetlen) {
+	        fprintf(stderr, "Received truncated message.\n");
+		return -1;
+	    }
+	    if(compare_hmac(src, dst, packet, bodylen,
+			    packet + i + 2 , len) == 1) {
+		return 1;
+	    }
+	}
+	i += len + 2;
+    }
+    return 0;
+}

hmac.h

+/*
+Copyright (c) 2018 by Clara Dô and Weronika Kolodziejak
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+*/
+
+#define DIGEST_LEN 20
+#define SHA1_BLOCK_SIZE 64
+#define RIPEMD160_BLOCK_SIZE 64
+
+struct key *find_key(const char *id);
+struct key *retain_key(struct key *key);
+void release_key(struct key *key);
+struct key *add_key(char *id, int type, int len, unsigned char *value);
+int add_hmac(struct buffered *buf, struct interface *ifp,
+             unsigned char *packet_header);
+int check_hmac(const unsigned char *packet, int packetlen, int bodylen,
+	       const unsigned char *src, const unsigned char *dst);

interface.c

@@ -42,6 +42,7 @@ THE SOFTWARE.
 #include "configuration.h"
 #include "local.h"
 #include "xroute.h"
+#include "hmac.h"
 
 struct interface *interfaces = NULL;
 
@@ -474,6 +475,15 @@ interface_updown(struct interface *ifp, int up)
         update_interface_metric(ifp);
         rc = check_interface_ipv4(ifp);
 
+        if(IF_CONF(ifp, key) != ifp->key) {
+            if(ifp->key != NULL)
+                release_key(ifp->key);
+            if(IF_CONF(ifp, key) != NULL)
+                ifp->key = retain_key(IF_CONF(ifp, key));
+            else
+                ifp->key = NULL;
+        }
+
         debugf("Upped interface %s (cost=%d, channel=%d%s).\n",
                ifp->name,
                ifp->cost,

interface.h

@@ -35,6 +35,13 @@ struct buffered_update {
 #define IF_TYPE_TUNNEL 3
 
 /* If you modify this structure, also modify the merge_ifconf function. */
+struct key {
+    char *id;
+    int type;
+    int len;
+    unsigned char *value;
+    unsigned short ref_count;
+};
 
 struct interface_conf {
     char *ifname;
@@ -53,6 +60,7 @@ struct interface_conf {
     unsigned int rtt_min;
     unsigned int rtt_max;
     unsigned int max_rtt_penalty;
+    struct key *key;
     struct interface_conf *next;
 };
 
@@ -102,6 +110,8 @@ struct buffered {
     int hello;
 };
 
+#define INDEX_LEN 8
+
 struct interface {
     struct interface *next;
     struct interface_conf *conf;
@@ -131,6 +141,9 @@ struct interface {
     unsigned int rtt_min;
     unsigned int rtt_max;
     unsigned int max_rtt_penalty;
+    struct key *key;
+    unsigned int pc;
+    unsigned char index[INDEX_LEN];
 };
 
 #define IF_CONF(_ifp, _field) \

message.c

@@ -27,6 +27,7 @@ THE SOFTWARE.
 #include <sys/time.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
+#include <time.h>
 
 #include "babeld.h"
 #include "util.h"
@@ -40,6 +41,7 @@ THE SOFTWARE.
 #include "resend.h"
 #include "message.h"
 #include "configuration.h"
+#include "hmac.h"
 
 unsigned char packet_header[4] = {42, 2};
 
@@ -248,7 +250,7 @@ parse_ihu_subtlv(const unsigned char *a, int alen,
 {
     int type, len, i = 0;
     int have_timestamp = 0;
-    unsigned int timestamp1, timestamp2;
+    unsigned int timestamp1 = 0, timestamp2 = 0;
 
     while(i < alen) {
         type = a[0];
@@ -293,9 +295,8 @@ parse_ihu_subtlv(const unsigned char *a, int alen,
         *timestamp1_return = timestamp1;
         *timestamp2_return = timestamp2;
     }
-    if(have_timestamp_return) {
+    if(have_timestamp_return)
         *have_timestamp_return = have_timestamp;
-    }
     return 1;
 }
 
@@ -439,9 +440,100 @@ network_address(int ae, const unsigned char *a, unsigned int len,
     return network_prefix(ae, -1, 0, a, NULL, len, a_r);
 }
 
+static int
+preparse_packet(const unsigned char *packet, int bodylen,
+                struct neighbour *neigh, struct interface *ifp)
+{
+    int i;
+    const unsigned char *message;
+    unsigned char type, len;
+    int challenge_success = 0;
+    int have_index = 0, index_len;
+    unsigned char pc[4], index[256];
+
+    i = 0;
+    while(i < bodylen) {
+	message = packet + 4 + i;
+	type = message[0];
+	if(type == MESSAGE_PAD1) {
+	    i++;
+	    continue;
+	}
+	if(i + 1 > bodylen) {
+            fprintf(stderr, "Received truncated message.\n");
+            break;
+        }
+	len = message[1];
+	if(i + len > bodylen) {
+            fprintf(stderr, "Received truncated message.\n");
+            break;
+        }
+	if(type == MESSAGE_CRYPTO_SEQNO) {
+            if(len < 4) {
+                fprintf(stderr, "Received truncated PC TLV.\n");
+                break;
+            }
+            if(len > 4 + 32) {
+                fprintf(stderr, "Overlong PC TLV.\n");
+                break;
+            }
+            debugf("Received PC from %s.\n",
+                   format_address(neigh->address));
+            memcpy(pc, message + 2, 4);
+            index_len = len - 4;
+            memcpy(index, message + 6, len - 4);
+            have_index = 1;
+        } else if(type == MESSAGE_CHALLENGE_RESPONSE) {
+            debugf("Received challenge response from %s.\n",
+                   format_address(neigh->address));
+	    gettime(&now);
+	    if(len == sizeof(neigh->nonce) &&
+               memcmp(neigh->nonce, message + 2, len) == 0 &&
+	       timeval_compare(&now, &neigh->challenge_deadline) <= 0) {
+                challenge_success = 1;
+            } else {
+                debugf("Challenge failed.\n");
+            }
+	} else if(type == MESSAGE_CHALLENGE_REQUEST) {
+	    unsigned char nonce[len];
+            debugf("Received challenge request from %s.\n",
+                   format_address(neigh->address));
+	    memcpy(nonce, message + 2, len);
+	    send_challenge_reply(neigh, nonce, len);
+	}
+	i += len + 2;
+    }
+
+    if(!have_index) {
+        debugf("No PC in packet.\n");
+        return 0;
+    }
+
+    if(neigh->have_index && neigh->index_len == index_len &&
+       memcmp(index, neigh->index, index_len) == 0) {
+        if(memcmp(neigh->pc, pc, 4) < 0) {
+            memcpy(neigh->pc, pc, 4);
+            return 1;
+        } else {
+            debugf("Out of order PC.\n");
+            return 0;
+        }
+    } else if(challenge_success) {
+        neigh->index_len = index_len;
+        memcpy(neigh->index, index, index_len);
+        memcpy(neigh->pc, pc, 4);
+        neigh->have_index = 1;
+        return 1;
+    } else {
+        send_challenge_req(neigh);
+        return 0;
+    }
+}
+
 void
 parse_packet(const unsigned char *from, struct interface *ifp,
-             const unsigned char *packet, int packetlen)
+             const unsigned char *packet, int packetlen,
+	     const unsigned char *to)
 {
     int i;
     const unsigned char *message;
@@ -494,6 +586,19 @@ parse_packet(const unsigned char *from, struct interface *ifp,
         return;
     }
 
+    if(ifp->key != NULL) {
+	if(check_hmac(packet, packetlen, bodylen, neigh->address,
+		      to) != 1) {
+	    fprintf(stderr, "Received wrong hmac.\n");
+	    return;
+	}
+
+	if(preparse_packet(packet, bodylen, neigh, ifp) == 0) {
+	    fprintf(stderr, "Received wrong PC or failed the challenge.\n");
+	    return;
+	}
+    }
+
     i = 0;
     while(i < bodylen) {
         message = packet + 4 + i;
@@ -832,6 +937,10 @@ parse_packet(const unsigned char *from, struct interface *ifp,
                    format_eui64(message + 8), seqno);
             handle_request(neigh, prefix, plen, src_prefix, src_plen,
                            message[6], seqno, message + 8);
+        } else if(type == MESSAGE_CRYPTO_SEQNO ||
+		  type == MESSAGE_CHALLENGE_REQUEST ||
+		  type == MESSAGE_CHALLENGE_RESPONSE) {
+            /* We're dealing with these in preparse_packet. */
         } else {
             debugf("Received unknown packet type %d from %s on %s.\n",
                    type, format_address(from), ifp->name);
@@ -913,16 +1022,26 @@ void
 flushbuf(struct buffered *buf, struct interface *ifp)
 {
     int rc;
+    int end = buf->len;
 
     assert(buf->len <= buf->size);
 
     if(buf->len > 0) {
+        if(ifp->key != NULL && ifp->key->type != 0)
+            send_crypto_seqno(buf, ifp);
         debugf("  (flushing %d buffered bytes)\n", buf->len);
         DO_HTONS(packet_header + 2, buf->len);
         fill_rtt_message(buf, ifp);
+        if(ifp->key != NULL && ifp->key->type != 0) {
+            end = add_hmac(buf, ifp, packet_header);
+            if(end < 0) {
+                fprintf(stderr, "Couldn't add HMAC.\n");
+                return;
+            }
+        }
         rc = babel_send(protocol_socket,
                         packet_header, sizeof(packet_header),
-                        buf->buf, buf->len,
+                        buf->buf, end,
                         (struct sockaddr*)&buf->sin6,
                         sizeof(buf->sin6));
         if(rc < 0)
@@ -962,6 +1081,8 @@ schedule_flush_now(struct buffered *buf)
 static void
 ensure_space(struct buffered *buf, struct interface *ifp, int space)
 {
+    if(ifp->key != NULL)
+        space += MAX_HMAC_SPACE + 6 + NONCE_LEN;
     if(buf->size - buf->len < space)
         flushbuf(buf, ifp);
 }
@@ -969,7 +1090,9 @@ ensure_space(struct buffered *buf, struct interface *ifp, int space)
 static void
 start_message(struct buffered *buf, struct interface *ifp, int type, int len)
 {
-    if(buf->size - buf->len < len + 2)
+    int space =
+        ifp->key == NULL ? len + 2 : len + 2 + MAX_HMAC_SPACE + 6 + NONCE_LEN;
+    if(buf->size - buf->len < space)
         flushbuf(buf, ifp);
     buf->buf[buf->len++] = type;
     buf->buf[buf->len++] = len;
@@ -1012,6 +1135,23 @@ accumulate_bytes(struct buffered *buf,
     buf->len += len;
 }
 
+int
+send_crypto_seqno(struct buffered *buf, struct interface *ifp)
+{
+    if(ifp->pc == 0) {
+        int rc;
+	rc = read_random_bytes(ifp->index, INDEX_LEN);
+        if(rc < INDEX_LEN)
+            return -1;
+    }
+    start_message(buf, ifp, MESSAGE_CRYPTO_SEQNO, 4 + INDEX_LEN);
+    accumulate_int(buf, ifp->pc);
+    accumulate_bytes(buf, ifp->index, INDEX_LEN);
+    end_message(buf, MESSAGE_CRYPTO_SEQNO, 4 + INDEX_LEN);
+    ifp->pc++;
+    return 1;
+}
+
 void
 send_ack(struct neighbour *neigh, unsigned short nonce, unsigned short interval)
 {
@@ -1024,6 +1164,36 @@ send_ack(struct neighbour *neigh, unsigned short nonce, unsigned short interval)
     schedule_flush_ms(&neigh->buf, roughly(interval * 6));
 }
 
+int
+send_challenge_req(struct neighbour *neigh)
+{
+    int rc;
+    debugf("Sending challenge request to %s on %s.\n",
+	   format_address(neigh->address), neigh->ifp->name);
+    rc = read_random_bytes(neigh->nonce, NONCE_LEN);
+    if(rc < NONCE_LEN)
+        return -1;
+    start_message(&neigh->buf, neigh->ifp, MESSAGE_CHALLENGE_REQUEST, NONCE_LEN);
+    accumulate_bytes(&neigh->buf, neigh->nonce, NONCE_LEN);
+    end_message(&neigh->buf, MESSAGE_CHALLENGE_REQUEST, NONCE_LEN);
+    gettime(&now);
+    timeval_add_msec(&neigh->challenge_deadline, &now, 300);
+    schedule_flush_now(&neigh->buf);
+    return 1;
+}
+
+void
+send_challenge_reply(struct neighbour *neigh, unsigned char *crypto_nonce,
+		     int len)
+{
+    debugf("Sending challenge reply to %s on %s.\n",
+	   format_address(neigh->address), neigh->ifp->name);
+    start_message(&neigh->buf, neigh->ifp, MESSAGE_CHALLENGE_RESPONSE, len);
+    accumulate_bytes(&neigh->buf, crypto_nonce, len);
+    end_message(&neigh->buf, MESSAGE_CHALLENGE_RESPONSE, len);
+    schedule_flush_now(&neigh->buf);
+}
+
 static void
 buffer_hello(struct buffered *buf, struct interface *ifp,
              unsigned short seqno, unsigned interval, int unicast)
@@ -1703,7 +1873,6 @@ send_ihu(struct neighbour *neigh, struct interface *ifp)
         return;
     }
 
-
     if(ifp && neigh->ifp != ifp)
         return;
 
@@ -1948,6 +2117,7 @@ send_multicast_multihop_request(struct interface *ifp,
                               src_prefix, src_plen,
                               seqno, id, hop_count);
     }
+
 }
 
 void

message.h

@@ -21,6 +21,7 @@ THE SOFTWARE.
 */
 
 #define MAX_BUFFERED_UPDATES 200
+#define MAX_HMAC_SPACE 48
 
 #define MESSAGE_PAD1 0
 #define MESSAGE_PADN 1
@@ -34,6 +35,11 @@ THE SOFTWARE.
 #define MESSAGE_REQUEST 9
 #define MESSAGE_MH_REQUEST 10
 
+#define MESSAGE_CRYPTO_SEQNO 121
+#define MESSAGE_HMAC 122
+#define MESSAGE_CHALLENGE_REQUEST 123
+#define MESSAGE_CHALLENGE_RESPONSE 124
+
 /* Protocol extension through sub-TLVs. */
 #define SUBTLV_PAD1 0
 #define SUBTLV_PADN 1
@@ -50,11 +56,15 @@ extern int split_horizon;
 extern unsigned char packet_header[4];
 
 void parse_packet(const unsigned char *from, struct interface *ifp,
-                  const unsigned char *packet, int packetlen);
+                  const unsigned char *packet, int packetlen,
+		  const unsigned char *to);
 void flushbuf(struct buffered *buf, struct interface *ifp);
 void flushupdates(struct interface *ifp);
+int send_crypto_seqno(struct buffered *buf, struct interface *ifp);
 void send_ack(struct neighbour *neigh, unsigned short nonce,
               unsigned short interval);
+int send_challenge_req(struct neighbour *neigh);
+void send_challenge_reply(struct neighbour *neigh, unsigned char *crypto_nonce, int len);
 void send_multicast_hello(struct interface *ifp, unsigned interval, int force);
 void send_unicast_hello(struct neighbour *neigh, unsigned interval, int force);
 void send_hello(struct interface *ifp);

neighbour.c

@@ -34,6 +34,7 @@ THE SOFTWARE.
 #include "interface.h"
 #include "neighbour.h"
 #include "source.h"
+#include "hmac.h"
 #include "route.h"
 #include "message.h"
 #include "resend.h"
@@ -105,7 +106,9 @@ find_neighbour(const unsigned char *address, struct interface *ifp)
     neigh->ihu_time = now;
     neigh->hello.time = neigh->uhello.time = zero;
     neigh->hello_rtt_receive_time = zero;
+    neigh->echo_receive_time = zero;
     neigh->rtt_time = zero;
+    neigh->challenge_deadline = now;
     neigh->ifp = ifp;
     neigh->buf.buf = buf;
     neigh->buf.size = ifp->buf.size;

neighbour.h

@@ -27,6 +27,8 @@ struct hello_history {
     struct timeval time;
 };
 
+#define NONCE_LEN 8
+
 struct neighbour {
     struct neighbour *next;
     /* This is -1 when unknown, so don't make it unsigned */
@@ -42,8 +44,15 @@ struct neighbour {
        according to remote clock. */
     unsigned int hello_send_us;
     struct timeval hello_rtt_receive_time;
+    struct timeval echo_receive_time;
     unsigned int rtt;
     struct timeval rtt_time;
+    int have_index;
+    int index_len;
+    unsigned char pc[4];
+    unsigned char index[32];
+    unsigned char nonce[NONCE_LEN];
+    struct timeval challenge_deadline;
     struct interface *ifp;
     struct buffered buf;
 };

net.c

@@ -29,6 +29,7 @@ THE SOFTWARE.
 #include <sys/uio.h>
 #include <sys/socket.h>
 #include <sys/un.h>
+#define __USE_GNU
 #include <netinet/in.h>
 #include <netinet/in_systm.h>
 #include <netinet/ip.h>
@@ -84,6 +85,10 @@ babel_socket(int port)
     if(rc < 0)
         perror("Couldn't set traffic class");
 
+    rc = setsockopt(s, IPPROTO_IPV6, IPV6_RECVPKTINFO, &one, sizeof(one));
+    if(rc < 0)
+	goto fail;
+
     rc = fcntl(s, F_GETFL, 0);
     if(rc < 0)
         goto fail;
@@ -117,11 +122,15 @@ babel_socket(int port)
 }
 
 int
-babel_recv(int s, void *buf, int buflen, struct sockaddr *sin, int slen)
+babel_recv(int s, void *buf, int buflen, struct sockaddr *sin, int slen,
+	   unsigned char *src_return)
 {
     struct iovec iovec;
     struct msghdr msg;
-    int rc;
+    unsigned char cmsgbuf[128];
+    struct cmsghdr *cmsg;
+    int rc, found;
+    unsigned char src[16] = {0};
 
     memset(&msg, 0, sizeof(msg));
     iovec.iov_base = buf;
@@ -130,8 +139,33 @@ babel_recv(int s, void *buf, int buflen, struct sockaddr *sin, int slen)
     msg.msg_namelen = slen;
     msg.msg_iov = &iovec;
     msg.msg_iovlen = 1;
+    msg.msg_control = cmsgbuf;
+    msg.msg_controllen = sizeof(cmsgbuf);
 
     rc = recvmsg(s, &msg, 0);
+    if(rc < 0)
+	return rc;
+
+    found = 0;
+    memset(src, 0, 16);
+    cmsg = CMSG_FIRSTHDR(&msg);
+    while(cmsg != NULL) {
+	if(cmsg->cmsg_level == IPPROTO_IPV6 &&
+	   cmsg->cmsg_type == IPV6_PKTINFO) {
+	    struct in6_pktinfo *info =(struct in6_pktinfo*)CMSG_DATA(cmsg);
+	    memcpy(src, info->ipi6_addr.s6_addr, 16);
+	    found = 1;
+	    break;
+	}
+	cmsg = CMSG_NXTHDR(&msg, cmsg);
+    }
+
+    if(!found) {
+	errno = EDESTADDRREQ;
+	return -1;
+    }
+    if(src_return != NULL)
+	memcpy(src_return, src, 16);
     return rc;
 }
 

net.h

@@ -21,7 +21,8 @@ THE SOFTWARE.
 */
 
 int babel_socket(int port);
-int babel_recv(int s, void *buf, int buflen, struct sockaddr *sin, int slen);
+int babel_recv(int s, void *buf, int buflen, struct sockaddr *sin, int slen,
+	   unsigned char *src_return);
 int babel_send(int s,
                const void *buf1, int buflen1, const void *buf2, int buflen2,
                const struct sockaddr *sin, int slen);

util.c

@@ -197,6 +197,38 @@ parse_thousands(const char *string)
     return -1;
 }
 
+int
+h2i(char c)
+{
+    if(c >= '0' && c <= '9')
+	return c - '0';
+    else if(c >= 'a' && c <= 'f')
+	return c - 'a' + 10;
+    else if(c >= 'A' && c <= 'F')
+	return c - 'A' + 10;
+    else
+	return -1;
+}
+
+int
+fromhex(unsigned char *dest, char *src, int n)
+{
+    int i;
+    if(n % 2 != 0)
+	return -1;
+    for(i = 0; i < n/2; i++) {
+	int a, b;
+	a = h2i(src[i*2]);
+	if(a < 0)
+	    return -1;
+	b = h2i(src[i*2 + 1]);
+	if(b < 0)
+	    return -1;
+	dest[i] = a*16 + b;
+    }
+    return n/2;
+}
+
 void
 do_debugf(int level, const char *format, ...)
 {

util.h

@@ -79,6 +79,8 @@ void timeval_min(struct timeval *d, const struct timeval *s);
 void timeval_min_sec(struct timeval *d, time_t secs);
 int parse_nat(const char *string) ATTRIBUTE ((pure));
 int parse_thousands(const char *string) ATTRIBUTE ((pure));
+int h2i(char c);
+int fromhex(unsigned char *dest, char *src, int n);
 void do_debugf(int level, const char *format, ...)
     ATTRIBUTE ((format (printf, 2, 3))) COLD;
 int in_prefix(const unsigned char *restrict address,