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Message formatting, authentication, and error detection in home control systems
| Details |
Inventors: Odinak, Gilad; Keam, Nigel S.;
Assignee: Microsoft Corporation (Redmond, WA)
Primary Examiner: Zimmerman; Brian
Assistant Examiner:
Attorney, Agent or Firm: Lee & Hayes, PLLC
A system for communicating over electrical wiring in a house or other building is presented. 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. |
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DETAILED DESCRIPTION The invention includes groups of sending and receiving components that communicate using household electrical wiring.
Often, such a group is a pair of components, one of which is a controlling component such as a switch module, and another of which is a controlled component such as a switchable power receptacle.
The components of an individual group communicate by sending and receiving discrete messages between themselves.
Each group of components is assigned a unique group identifier code, and messages between components of a group each include the group identifier code of that group.
Although individual components receive messages from other groups, they are configured to disregard such messages that have group identifier codes that are different than that of the group to which the component belongs.
Thus, although all components share the same transmission medium, virtual connections are formed between individual components based on their group identifier codes.
The codes require fewer bits to encode than traditional source/destination addresses such as used in the prior art.
Messages are authenticated using a message authentication code that is calculated for and included in each message.
The message authentication code for a message within a particular group is derived from message data and from a key value that is shared between the components of the group.
A one-way hash function is used to calculate the key value.
The shared key value changes, at the discretion of one or more components of the group.
Rather than transmitting a new key value when a change is desired, each component has information that enables it to independently calculate a common sequence of key values.
When a key change occurs, each component of the group starts using the next key value in the sequence.
More specifically, key values are calculated using a one-way hash function, based on a common and unchanging seed value, and a counter that is incremented by one for each sequential key value
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