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Overlay mode with address summarisation closer to working.

Browse Source 
Self-announcements now abbreviate addresses, and in theory they
get expanded on reception -- but more testing and coding required.
This commit is contained in:
gardners 2011-08-15 09:27:29 +02:00
parent f8064a1795
commit 229850c8d7
5 changed files with 360 additions and 71 deletions
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102
mphlr.h
View File

@ -405,6 +405,8 @@ typedef struct overlay_interface {
int tick_ms; int tick_ms;
/* The time of the last tick on this interface in milli seconds */ /* The time of the last tick on this interface in milli seconds */
long long last_tick_ms; long long last_tick_ms;
/* How many times have we abbreviated our address since we last announced it in full? */
int ticks_since_sent_full_address;
/* Sequence number of last tick. Sent with announcments to help keep track of the reliability of /* Sequence number of last tick. Sent with announcments to help keep track of the reliability of
getting traffic to/from us. */ getting traffic to/from us. */
@ -589,8 +591,52 @@ int overlay_get_nexthop(overlay_payload *p,unsigned char *nexthop,int *nexthople
extern int overlay_interface_count; extern int overlay_interface_count;
/* Userland overlay mesh packet codes */ /* Overlay mesh packet codes */
#define OF_SELFANNOUNCE 0x01 #define OF_TYPE_BITS 0xf0
#define OF_TYPE_SELFANNOUNCE 0x10 /* BATMAN style announcement frames */
#define OF_TYPE_SELFANNOUNCE_ACK 0x20 /* BATMAN style "I saw your announcment" frames */
#define OF_TYPE_DATA 0x30 /* Ordinary data frame.
Upto MTU bytes of payload.
16 bit channel/port indicator for each end.
*/
#define OF_TYPE_DATA_VOICE 0x40 /* Voice data frame.
Limited to 255 bytes of payload.
1 byte channel/port indicator for each end */
#define OF_TYPE_RHIZOME_ADVERT 0x50 /* Advertisment of file availability via Rhizome */
#define OF_TYPE_RESERVED_06 0x60
#define OF_TYPE_RESERVED_07 0x70
#define OF_TYPE_RESERVED_08 0x80
#define OF_TYPE_RESERVED_09 0x90
#define OF_TYPE_RESERVED_0a 0xa0
#define OF_TYPE_RESERVED_0b 0xb0
#define OF_TYPE_RESERVED_0c 0xc0
#define OF_TYPE_RESERVED_0d 0xd0
#define OF_TYPE_EXTENDED12 0xe0 /* modifier bits and next byte provide 12 bits extended format
(for future expansion, just allows us to skip the frame) */
#define OF_TYPE_EXTENDED20 0xf0 /* modifier bits and next 2 bytes provide 20 bits extended format
(for future expansion, just allows us to skip the frame) */
/* Flags used to control the interpretation of the resolved type field */
#define OF_TYPE_FLAG_BITS 0xf0000000
#define OF_TYPE_FLAG_NORMAL 0x0
#define OF_TYPE_FLAG_E12 0x10000000
#define OF_TYPE_FLAG_E20 0x00000000
/* Modifiers that indicate the disposition of the frame */
#define OF_MODIFIER_BITS 0x0f
/* Crypto/security options */
#define OF_CRYPTO_BITS 0x0c
#define OF_CRYPTO_NONE 0x00
#define OF_CRYPTO_CIPHERED 0x04 /* Encrypted frame */
#define OF_CRYPTO_SIGNED 0x08 /* Encrypted and Digitally signed frame */
#define OF_CRYPTO_PARANOID 0x0c /* Encrypted and digitally signed frame, with final destination address also encrypted. */
/* Data compression */
#define OF_COMPRESS_BITS 0x03
#define OF_COMPRESS_NONE 0x00
#define OF_COMPRESS_GZIP 0x01 /* Frame compressed with gzip */
#define OF_COMPRESS_BZIP2 0x02 /* bzip2 */
#define OF_COMPRESS_RESERVED 0x03 /* Reserved for another compression system */
#define OVERLAY_ADDRESS_CACHE_SIZE 1024 #define OVERLAY_ADDRESS_CACHE_SIZE 1024
int overlay_abbreviate_address(unsigned char *in,char *out,int *ofs); int overlay_abbreviate_address(unsigned char *in,char *out,int *ofs);
@ -600,7 +646,53 @@ int overlay_abbreviate_cache_lookup(unsigned char *in,unsigned char *out,int *of
int prefix_bytes,int index_bytes); int prefix_bytes,int index_bytes);
int overlay_abbreviate_remember_index(int index_byte_count,unsigned char *in,unsigned char *index_bytes); int overlay_abbreviate_remember_index(int index_byte_count,unsigned char *in,unsigned char *index_bytes);
/* Return codes for resolution of abbreviated addressses */
#define OA_RESOLVED 0 /* We expanded the abbreviation */ #define OA_UNINITIALISED 0 /* Nothing has been written into the field */
#define OA_RESOLVED 1 /* We expanded the abbreviation successfully */
#define OA_PLEASEEXPLAIN 1 /* We need the sender to explain their abbreviation */ #define OA_PLEASEEXPLAIN 1 /* We need the sender to explain their abbreviation */
#define OA_UNSUPPORTED 2 /* We cannot expand the abbreviation as we do not understand this code */ #define OA_UNSUPPORTED 3 /* We cannot expand the abbreviation as we do not understand this code */
/* Codes used to describe abbreviated addresses.
Values 0x10 - 0xff are the first byte of, and implicit indicators of addresses written in full */
#define OA_CODE_00 0x00
#define OA_CODE_INDEX 0x01
#define OA_CODE_02 0x02
#define OA_CODE_PREVIOUS 0x03
#define OA_CODE_04 0x04
#define OA_CODE_PREFIX3 0x05
#define OA_CODE_PREFIX7 0x06
#define OA_CODE_PREFIX11 0x07
#define OA_CODE_FULL_INDEX1 0x08
#define OA_CODE_PREFIX3_INDEX1 0x09
#define OA_CODE_PREFIX7_INDEX1 0x0a
#define OA_CODE_PREFIX11_INDEX1 0x0b
#define OA_CODE_0C 0x0c
#define OA_CODE_PREFIX11_INDEX2 0x0d
#define OA_CODE_FULL_INDEX2 0x0e
/* The TTL field in a frame is used to differentiate between link-local and wide-area broadcasts */
#define OA_CODE_BROADCAST 0x0f
typedef struct overlay_frame {
unsigned int type;
unsigned int modifiers;
unsigned char nexthop[32];
int nexthop_address_status;
unsigned char destination[32];
int destination_address_status;
unsigned char source[32];
int source_address_status;
/* Frame content from destination address onwards */
unsigned int bytecount;
unsigned char *bytes;
/* Actual payload */
unsigned int payloadlength;
unsigned char *payload;
int rfs; /* remainder of frame size */
} overlay_frame;

7
overlay.c
View File

@ -103,4 +103,11 @@ int overlayServerMode()
/* Check if we need to trigger any ticks on any interfaces */ /* Check if we need to trigger any ticks on any interfaces */
overlay_check_ticks(); overlay_check_ticks();
} }
return 0;
}
int overlay_frame_process(overlay_frame *f)
{
return WHY("Not implemented");
} }

33
overlay_abbreviations.c
View File

@ -21,7 +21,7 @@
0x0c = reserved. 0x0c = reserved.
0x0d = same as 0x07, but assign two byte index. 0x0d = same as 0x07, but assign two byte index.
0x0e = full address followed by two-byte index allocation. 0x0e = full address followed by two-byte index allocation.
0x0f = broadcast. 0x0f = broadcast link-local.
However, in this implementation we not include support for the two-byte However, in this implementation we not include support for the two-byte
index code, as it requires 64Kx32=2MB storage, which is too much to ask index code, as it requires 64Kx32=2MB storage, which is too much to ask
@ -69,6 +69,10 @@
no more than 33 bytes. In any case, indicating the crypto system is not the problem of no more than 33 bytes. In any case, indicating the crypto system is not the problem of
this section, as we are just concerned with abbreviating and expanding the addresses. this section, as we are just concerned with abbreviating and expanding the addresses.
(A simple solution to the multiple crypto-system problem is to have the receiver try each
known crypto system when decoding a frame, and remember which addresses use which system.
Probably a reasonable solution for now.)
To decode abbreviations supplied by other nodes we need to try to replicate a copy of To decode abbreviations supplied by other nodes we need to try to replicate a copy of
their abbreviation table. This is where things get memory intensive (about 8KB per node). their abbreviation table. This is where things get memory intensive (about 8KB per node).
However, we only need the table of one-hop neighbours, and it is reasonable to have a However, we only need the table of one-hop neighbours, and it is reasonable to have a
@ -260,40 +264,41 @@ int overlay_abbreviate_expand_address(unsigned char *in,int *inofs,unsigned char
int bytes=0; int bytes=0;
switch(in[0]) switch(in[0])
{ {
case 0x00: case 0x02: case 0x04: case 0x0c: case OA_CODE_00: case OA_CODE_02: case OA_CODE_04: case OA_CODE_0C:
/* Unsupported codes, so tell the sender /* Unsupported codes, so tell the sender
if the frame was addressed to us as next-hop */ if the frame was addressed to us as next-hop */
(*inofs)++; (*inofs)++;
return OA_UNSUPPORTED; return OA_UNSUPPORTED;
case 0x01: /* single byte index look up */ case OA_CODE_INDEX: /* single byte index look up */
exit(WHY("Unimplemented address abbreviation code")); exit(WHY("Unimplemented address abbreviation code"));
break; break;
case 0x03: /* Same as last address */ case OA_CODE_PREVIOUS: /* Same as last address */
(*inofs)++; (*inofs)++;
bcopy(&overlay_abbreviate_previous_address.b[0],&out[*ofs],SID_SIZE); bcopy(&overlay_abbreviate_previous_address.b[0],&out[*ofs],SID_SIZE);
(*ofs)+=SID_SIZE; (*ofs)+=SID_SIZE;
return OA_RESOLVED; return OA_RESOLVED;
break; break;
case 0x05: case 0x09: /* 3-byte prefix */ case OA_CODE_PREFIX3: case OA_CODE_PREFIX3_INDEX1: /* 3-byte prefix */
if (in[0]==0x09) bytes=1; if (in[0]==0x09) bytes=1;
(*inofs)+=3+bytes; (*inofs)+=3+bytes;
return overlay_abbreviate_cache_lookup(in,out,ofs,3,bytes); return overlay_abbreviate_cache_lookup(in,out,ofs,3,bytes);
case 0x06: case 0x0a: /* 7-byte prefix */ case OA_CODE_PREFIX7: case OA_CODE_PREFIX7_INDEX1: /* 7-byte prefix */
if (in[0]==0x0a) bytes=1; if (in[0]==OA_CODE_PREFIX7_INDEX1) bytes=1;
(*inofs)+=7+bytes; (*inofs)+=7+bytes;
return overlay_abbreviate_cache_lookup(in,out,ofs,7,bytes); return overlay_abbreviate_cache_lookup(in,out,ofs,7,bytes);
case 0x07: case 0x0b: case 0x0d: /* 11-byte prefix */ case OA_CODE_PREFIX11: case OA_CODE_PREFIX11_INDEX1: case OA_CODE_PREFIX11_INDEX2: /* 11-byte prefix */
if (in[0]==0x0b) bytes=1; if (in[0]==OA_CODE_PREFIX11_INDEX1) bytes=1;
if (in[0]==0x0d) bytes=2; if (in[0]==OA_CODE_PREFIX11_INDEX2) bytes=2;
(*inofs)+=11+bytes; (*inofs)+=11+bytes;
return overlay_abbreviate_cache_lookup(in,out,ofs,11,bytes); return overlay_abbreviate_cache_lookup(in,out,ofs,11,bytes);
case 0x0f: /* broadcast */ case OA_CODE_BROADCAST: /* broadcast */
memset(&out[*ofs],0xff,SID_SIZE); memset(&out[*ofs],0xff,SID_SIZE);
(*inofs)++; (*inofs)++;
return 0; return 0;
case 0x08: case 0x0e: default: /* Full address, optionally followed by index for us to remember */ case OA_CODE_FULL_INDEX1: case OA_CODE_FULL_INDEX2:
if (in[0]==0x08) bytes=1; default: /* Full address, optionally followed by index for us to remember */
if (in[0]==0x0e) bytes=2; if (in[0]==OA_CODE_FULL_INDEX1) bytes=1;
if (in[0]==OA_CODE_FULL_INDEX2) bytes=2;
bcopy(in,&out[*ofs],SID_SIZE); bcopy(in,&out[*ofs],SID_SIZE);
if (bytes) overlay_abbreviate_remember_index(bytes,in,&in[SID_SIZE]); if (bytes) overlay_abbreviate_remember_index(bytes,in,&in[SID_SIZE]);
(*inofs)+=SID_SIZE+bytes; (*inofs)+=SID_SIZE+bytes;

237
overlay_packetformats.c Normal file
View File

@ -0,0 +1,237 @@
#include "mphlr.h"
int packetOkOverlay(unsigned char *packet,int len,unsigned char *transaction_id,
struct sockaddr *recvaddr,int recvaddrlen,int parseP)
{
/*
Overlay packets are ensembles contain one or more frames each of which
should be handled separately.
There are two main types of enclosed frame.
1. Announcement frames which contain information that helps to maintain the
operation of the mesh.
and
2. Data frames that contain messages directed to nodes on the mesh.
In both instances we allow the contained addresses to be shortened to save bandwidth,
especially for low-bandwidth links.
All frames have the following fields:
Frame type (8bits)
Remaining frame size (RFS) (8bits for <256 bytes, 16bits for <510 bytes etc)
Next hop (variable length due to address abbreviation)
Destination (variable length due to address abbreviation)*
Source (variable length due to address abbreviation)*
Payload (length = RFS- len(frame type) - len(next hop)*
This structure is intended to allow relaying nodes to quickly ignore frames that are
not addressed to them as either the next hop or final destination.
The RFS field uses additional bytes to encode the length of longer frames.
This provides us with a slight space saving for the common case of short frames.
* Indicates fields that may be encrypted. The source and destination addresses can
be encrypted for paranoid traffic so that only the hops along the route know who is
talking to whom. This is not totally secure, but does prevent collateral eaves dropping
of frames by 4th parties. Paranoid communities could elect to only use nodes they trust
to carry the frame. And finally, the frame payload itself can be enciphered with the
final destination's public key, so that it is not possible even for the relaying 3rd
parties to observe the content.
Naturally some information will leak simply based on the size, periodicity and other
characteristics of the traffic, and some 3rd parties may be malevolent, so noone should
assume that this provides complete security.
Paranoid mode introduces a bandwidth cost of one signature, and a potentially substantial
energy cost of requiring every node along the delivery path to decrypt and reencrypt the
frame.
It would also be possible to design a super-paranoid mode where source routing is used with
concentric shells of encryption so that each hop can only work out the next hop to send it
to. However, that would result in rather large frames, and require an on-demand routing
approach which may well betray more information than the super-paranoid mode would hide.
Note also that it is possible to dispatch frames on a local link which are addressed to
broadcast, but are enciphered. In that situation only the intended recipient can
decode the frame, but at the cost of having all nodes on the local link having to decrypt
frame. Of course the nodes may elect to not decrypt such anonymous frames.
Such frames could even be flooded throughout part of the mesh by having the TTL>1, and
optionally with an anonymous source address to provide some plausible deniability for both
sending and reception if combined with a randomly selected TTL to give the impression of
the source having received the frame from elsewhere.
*/
int ofs;
overlay_frame f;
for(ofs=0;ofs<len;)
{
/* Clear out the data structure ready for next frame */
f.nexthop_address_status=OA_UNINITIALISED;
f.destination_address_status=OA_UNINITIALISED;
f.source_address_status=OA_UNINITIALISED;
/* Get normal form of packet type and modifiers */
f.type=packet[ofs]&OF_TYPE_BITS;
f.modifiers=packet[ofs]&OF_MODIFIER_BITS;
switch(packet[ofs]&OF_TYPE_BITS)
{
case OF_TYPE_EXTENDED20:
/* Eat the next two bytes and then skip over this reserved frame type */
f.type=OF_TYPE_FLAG_E20|(packet[ofs]&OF_MODIFIER_BITS)|(packet[ofs+2]<<12)|(packet[ofs+1]<<4);
f.modifiers=0;
ofs+=3;
break;
case OF_TYPE_EXTENDED12:
/* Eat the next byte and then skip over this reserved frame type */
f.type=OF_TYPE_FLAG_E12|(packet[ofs]&OF_MODIFIER_BITS)|(packet[ofs+1]<<4);
f.modifiers=0;
ofs+=2;
break;
case OF_TYPE_RESERVED_06:
case OF_TYPE_RESERVED_07:
case OF_TYPE_RESERVED_08:
case OF_TYPE_RESERVED_09:
case OF_TYPE_RESERVED_0a:
case OF_TYPE_RESERVED_0b:
case OF_TYPE_RESERVED_0c:
case OF_TYPE_RESERVED_0d:
case OF_TYPE_SELFANNOUNCE:
case OF_TYPE_SELFANNOUNCE_ACK:
case OF_TYPE_DATA:
case OF_TYPE_DATA_VOICE:
case OF_TYPE_RHIZOME_ADVERT:
/* No extra bytes to deal with here */
ofs++;
break;
}
/* Get length of remainder of frame */
f.rfs=packet[ofs];
while (packet[ofs]==0xff&&(ofs<len)&&(f.rfs<16384)) f.rfs+=packet[++ofs];
if (!f.rfs) {
/* Zero length -- assume we fell off the end of the packet */
break;
}
/* Now extract the next hop address */
int alen=0;
int offset=ofs;
f.nexthop_address_status=overlay_abbreviate_expand_address(packet,&offset,f.nexthop,&alen);
/* Now just make the rest of the frame available via the received frame structure, as the
frame may not be for us, so there is no point wasting time and energy if we don't have
to.
*/
f.bytes=&packet[ofs];
f.bytecount=f.rfs-(offset-ofs);
/* Finally process the frame */
overlay_frame_process(&f);
/* Skip the rest of the bytes in this frame so that we can examine the next one in this
ensemble */
fprintf(stderr,"ofs=%d, f.rfs=%d, len=%d\n",ofs,f.rfs,len);
ofs+=f.rfs;
}
return 0;
}
int overlay_add_selfannouncement(int interface,overlay_buffer *b)
{
/* Pull the first record from the HLR database and turn it into a
self-announcment. These are shorter than regular Subscriber Observation
Notices (SON) because they are just single-hop announcments of presence.
Do we really need to push the whole SID (32 bytes), or will just, say,
8 do so that we use a prefix of the SID which is still very hard to forge?
A hearer of a self-announcement who has not previously seen the sender might
like to get some authentication to prevent naughty people from spoofing routes.
We can do this by having ourselves, the sender, keep track of the last few frames
we have sent, so that we can be asked to sign them. Actually, we won't sign them,
as that is too slow/energy intensive, but we could use a D-H exchange with the neighbour,
performed once to get a shared secret that can be used to feed a stream cipher to
produce some sort of verification.
XXX - But this functionality really needs to move up a level to whole frame composition.
*/
unsigned char c;
int zero=0;
/* Make sure we can find our SID */
if (!findHlr(hlr,&zero,NULL,NULL)) return WHY("Could not find first entry in HLR");
/* Header byte */
c=OF_TYPE_SELFANNOUNCE;
if (ob_append_bytes(b,&c,1))
return WHY("ob_append_bytes() could not add self-announcement header");
int send_prefix=(overlay_interfaces[interface].ticks_since_sent_full_address<4);
/* Add space for Remaining Frame Size field. This will always be a single byte
for self-announcments as they are always <256 bytes. */
c=1+1+(send_prefix?(1+7):SID_SIZE)+4+1;
if (ob_append_bytes(b,&c,1))
return WHY("ob_append_bytes() could not add RFS for self-announcement frame");
/* Add next-hop address. Always link-local broadcast for self-announcements */
c=OA_CODE_BROADCAST;
if (ob_append_bytes(b,&c,1))
return WHY("ob_append_bytes() could not add self-announcement header");
/* Add final destination. Always broadcast for self-announcments.
As we have just referenced the broadcast address, we can encode it in a single byte */
c=OA_CODE_PREVIOUS;
if (ob_append_bytes(b,&c,1))
return WHY("ob_append_bytes() could not add self-announcement header");
/* Add our SID to the announcement as sender
We can likely get away with abbreviating our own address much of the time, since these
frames will be sent on a regular basis. However, we can only abbreviate using a prefix,
not any of the fancier methods. Indeed, if we tried to use the standard abbreviation
functions they would notice that we are attaching an address which is ourself, and send
a uselessly short address. So instead we will use a simple scheme where we will send our
address in full an arbitrary 1 in 4 times.
*/
if (overlay_interfaces[interface].ticks_since_sent_full_address>3)
{ if (ob_append_bytes(b,&hlr[zero+4],SID_SIZE)) return WHY("Could not append SID to self-announcement");
overlay_interfaces[interface].ticks_since_sent_full_address=0;
}
else
{
c=OA_CODE_PREFIX7;
if (ob_append_bytes(b,&c,1)) return WHY("ob_append_bytes() could not add address format code.");
if (ob_append_bytes(b,&hlr[zero+4],7)) return WHY("Could not append SID prefix to self-announcement");
overlay_interfaces[interface].ticks_since_sent_full_address++;
}
/* A sequence number, so that others can keep track of their reception of our frames.
These are per-interface */
if (ob_append_int(b,overlay_interfaces[interface].sequence_number))
return WHY("ob_append_int() could not add sequence number to self-announcement");
/* A TTL for this frame?
XXX - BATMAN uses various TTLs, but I think that it may just be better to have all TTL=1,
and have the onward nodes selectively choose which nodes to on-announce. If we prioritise
newly arrived nodes somewhat (or at least reserve some slots for them), then we can still
get the good news travels fast property of BATMAN, but without having to flood in the formal
sense. */
c=1;
if (ob_append_bytes(b,&c,1))
return WHY("ob_append_bytes() could not add TTL to self-announcement");
return 0;
}

52
overlay_route.c
View File

@ -1,57 +1,5 @@
#include "mphlr.h" #include "mphlr.h"
int overlay_add_selfannouncement(int interface,overlay_buffer *b)
{
/* Pull the first record from the HLR database and turn it into a
self-announcment. These are shorter than regular Subscriber Observation
Notices (SON) because they are just single-hop announcments of presence.
Do we really need to push the whole SID (32 bytes), or will just, say,
8 do so that we use a prefix of the SID which is still very hard to forge?
A hearer of a self-announcement who has not previously seen the sender might
like to get some authentication to prevent naughty people from spoofing routes.
We can do this by having ourselves, the sender, keep track of the last few frames
we have sent, so that we can be asked to sign them. Actually, we won't sign them,
as that is too slow/energy intensive, but we could use a D-H exchange with the neighbour,
performed once to get a shared secret that can be used to feed a stream cipher to
produce some sort of verification.
XXX - But this functionality really needs to move up a level to whole frame composition.
*/
unsigned char c;
int zero=0;
/* Make sure we can find our SID */
if (!findHlr(hlr,&zero,NULL,NULL)) return WHY("Could not find first entry in HLR");
/* Header byte */
c=OF_SELFANNOUNCE;
if (ob_append_bytes(b,&c,1))
return WHY("ob_append_bytes() could not add self-announcement header");
/* Add our SID to the announcement */
if (ob_append_bytes(b,&hlr[zero+4],SID_SIZE)) return WHY("Could not append SID to self-announcement");
/* A sequence number, so that others can keep track of their reception of our frames.
These are per-interface */
if (ob_append_int(b,overlay_interfaces[interface].sequence_number))
return WHY("ob_append_int() could not add sequence number to self-announcement");
/* A TTL for this frame?
XXX - BATMAN uses various TTLs, but I think that it may just be better to have all TTL=1,
and have the onward nodes selectively choose which nodes to on-announce. If we prioritise
newly arrived nodes somewhat (or at least reserve some slots for them), then we can still
get the good news travels fast property of BATMAN, but without having to flood in the formal
sense. */
c=1;
if (ob_append_bytes(b,&c,1))
return WHY("ob_append_bytes() could not add TTL to self-announcement");
return 0;
}
int overlay_get_nexthop(overlay_payload *p,unsigned char *nexthop,int *nexthoplen) int overlay_get_nexthop(overlay_payload *p,unsigned char *nexthop,int *nexthoplen)
{ {