Signatures

The signature-message, illustrated in figure 11.3, is attached to all outgoing OLSR packets. This message is to be the last message in the packet. Since the signature message is piggybacked to outgoing packets after the OLSR header for these packets is created, the OLSR packet header is adjusted to include the size of the signature message in the size field. The digest used as a signature is a hash created using the SHA-1 hashing algorithm which produces an irreversible 160-bit digest. The hash is based on the following:

• The OLSR packet header (with adjusted size).

• All OLSR messages in the packet except the signature message.

• The OLSR message header, the sub-header and the timestamp of the signature message.

• The shared secret key.

No considerations has to be taken regarding the variable fields of different headers (TTL, hop-count) as this signing is done hop-by-hop.