FANDA Multicast Data Format
Multicast packet format for Fairmount. All data is little endian on the wire.
NOTE That a UUID is 16 bytes long.
typedef struct udp_multicast_header
{
U16_t total_packet_length; /* Header length plus data payload */
U8_t version; /* current value = 1 or 2 (encrypted) */
U8_t flags; /* 1 = encrypted */
U32_t group_address; /* Multicast Group IP address */
UUID library_guid; /* GUID matching a library returned by GetNDL */
U16_t structure_id; /* structure ID attribute referenced in the NDL */
} Udp_Multicast_Header_t;
typedef struct udp_multicast_packet
{
Udp_Multicast_Header_t header; /* header information */
U8_t data[1500]; /* data to be interpreted per the NDL and will be a maximum of 1500 bytes */
} Udp_Multicast_Packet_t;
When encryption is in use, the NDL will include the following fields:
- Cipher
Cipher in use. One of the following strings:
*3DES
*AES128
*AES192
*AES256 - KeyBits
Number of bits in the encryption key - Rekey
Rekey interval in minutes
The
udp_multicast_packet
is wrapped as follows:
typedef struct udp_encrypted_packet
{
Udp_Multicast_Header_t header; /* header information */
U32_t key_generation; /* encryption key index */
U8_t iv[]; /* length depends on cipher in use */
U8_t enc_data[]; /* length from header.total_packet_length */
} Udp_Encrypted_Packet_t
header.version
will be at least 2.
header.flags
will have the low bit set to indicate that the packet is encrypted.
The encrypted plaintext is in the same format as for unencrypted multicasts with an added SHA1 hash at the end. The SHA1 is calculated over all data bytes, but does not include any header bytes.