Abstract: Described herein is a system for communicating over electrical wiring in a house or other building. Components are grouped and each group is assigned a group identifier code. Components communicates only with components of the same group, using the group identifier code. Each message includes the group identifier code, message data, and a message authentication code (MAC) that is calculated for each message. A receiving component disregards any message whose group identifier code is not the same as that of the receiving component. MACs are calculated using a shared key value and a one-way hash function. The shared key value, in turn, is taken from an ordered sequence of key values that is defined for each component group based on a counter value. To change to a new key value, one component of the group simply starts using the new key value. When a receiving component receives a message that does not authenticate using the current key value, it tries the next key value in the sequence.

Abstract: A system for electronic communications using electrical power lines in a building includes a plurality of components that are connected for communications among themselves through the electrical power lines. A control transmitter is associated with at least one of the components for transmitting a data stream over the electrical power lines as a series of state changes. The data stream has a sequence of binary elements that each have one of two possible binary values. The control transmitter is configured to encode the binary elements as a series of three different state intervals on the transmission medium, depending on the value of the current binary element, the immediately preceding binary element, and the immediately following binary element. A control receiver is configured to decode the original data stream based on the state intervals. The encoding scheme allows a bit rate that is equal to the baud rate of the transmission medium.