Two programs are present, dns_sender and dns_receiver, which respectively send and receive data only using DNS datagrams over UDP, while data are encoded to Base64 format.

The sender tries sending the data up to three times and with every packet, it expects a response from the receiver. If no response is received, sender tries to close the connection up to three times, and if the receiver responds to a connection-closing datagram, the communication is established again and transmission starts from the beginning. If, however, the connection could not be closed, the sender cannot send more data as they would confuse the receiver and the transmission is cancelled.

Patrik Skaloš (xskalo01), 2022

dns_sender [-u UPSTREAM_DNS_IP] {BASE_HOST} {DST_FILEPATH} [SRC_FILEPATH]

where:

• UPSTREAM_DNS_IP - IPv4 address of the DNS server to use. If not specified, first entry from resolv.conf is used
• BASE_HOST - domain (eg. example.com) to use in DNS datagrams
• DST_FILEPATH - path (relative) on the receiver's machine where to save the transmitted data
• SRC_FILEPATH - path (relative or absolute) to a file to send to the receiver. If not specified, input from STDIN is used instead

dns_sender -u 192.168.129.99 example.com file_received.txt file_to_send.txt

dns_receiver {BASE_HOST} {DST_DIRPATH}

where:

• BASE_HOST - domain (eg. example.com) to expect in incoming DNS datagrams
• DST_DIRPATH - path (relative or absolute) on the machine where to save files received from the sender

dns_receiver example.com files_received/