Communications Source Authentication

Abstract

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for authenticating a communications source. In one aspect, a method includes decrypting a symbol that was received over a particular communications channel. The symbol is decrypted using a decryption key that is assigned to a particular endpoint that is assigned the particular communications channel. A measure of error is computed for the decrypted symbol. In turn, a determination is made whether the measure of error exceeds a threshold error measure. If the measure of error does not exceed the threshold error measure the decrypted symbol is identified as a valid symbol transmitted by the particular endpoint, and logged as such. If the measure of error exceeds the threshold error measure, the decrypted symbol is identified as a symbol from a different endpoint; and

1 . A method performed by data processing apparatus, the method comprising:
 receiving a symbol over a particular communications channel;   decrypting the symbol using a decryption key that is assigned to a particular endpoint that is assigned the particular communications channel;   computing a measure of error for the decrypted symbol;   determining whether the measure of error exceeds a threshold error measure;   in response to determining that the measure of error exceeds the threshold error measure, identifying the decrypted symbol as a symbol from a different endpoint; and   in response to determining that the measure of error does not exceed the threshold error measure:
 identifying the decrypted symbol as a valid symbol transmitted by the particular endpoint; and 
 logging the valid symbol. 
   
     
     
         2 . The method of  claim 1 , further comprising:
 generating, by the particular endpoint, the symbol to include payload data and error correction data;   encrypting, by the particular endpoint, the symbol using an encryption key that is assigned to the particular endpoint; and   transmitting, by the particular endpoint, the encrypted symbol over the particular communications channel.   
     
     
         3 . The method of  claim 2 , wherein:
 generating the symbol comprises inserting an error correcting code into the payload data; and   encrypting the symbol comprises encrypting the symbol following insertion of the error correcting code.   
     
     
         4 . The method of  claim 1 , wherein:
 receiving a symbol comprises receiving a plurality of different symbols over a plurality of different communications channels, each different communications channel being assigned to a different endpoint; and   decrypting the symbol comprises, for each of the different communications channels, decrypting the symbol using a decryption key that is assigned to the endpoint to which the communications channel is assigned.   
     
     
         5 . The method of  claim 4 , further comprising retrieving, for each different endpoint, a different decryption key that is assigned to the different endpoint. 
     
     
         6 . The method of  claim 1 , wherein decrypting the symbol comprises decrypting the symbol with a symmetric key that has been assigned to the particular endpoint. 
     
     
         7 . The method of  claim 1 , wherein:
 computing a measure of error comprises computing a bit error rate for the decrypted symbol; and   determining whether the measure of error exceeds a threshold error measure comprises determining whether the bit error rate exceeds a threshold bit error rate.   
     
     
         8 . The method of  claim 1 , wherein receiving a symbol from a particular endpoint comprises receiving the symbol from a particular meter over a particular channel of a power line communications network. 
     
     
         9 . The method of  claim 8 , wherein decrypting the symbol comprises decrypting the symbol with a decryption key that is assigned to the particular meter. 
     
     
         10 . A method performed by data processing apparatus, the method comprising:
 receiving a symbol over a particular communications channel;   decrypting the symbol using a decryption key that is assigned to a particular endpoint that has been assigned to communicate over the particular communications channel;   determining that the symbol was transmitted by the particular endpoint, the determination being made based on a measure of error for the decrypted symbol not exceeding a threshold error measure; and   in response to determining that the symbol was transmitted by the particular endpoint, logging the decrypted symbol as a valid symbol.   
     
     
         11 . A computer storage medium encoded with a computer program, the program comprising instructions that when executed by data processing apparatus cause the data processing apparatus to perform operations comprising:
 receiving a symbol over a particular communications channel;   decrypting the symbol using a decryption key that is assigned to a particular endpoint that has been assigned to communicate over the particular communications channel;   determining that the symbol was transmitted by the particular endpoint, the determination being made based on a measure of error for the decrypted symbol not exceeding a threshold error measure; and   in response to determining that the symbol was transmitted by the particular endpoint, logging the decrypted symbol as a valid symbol.   
     
     
         12 . A system comprising:
 a set of endpoints in a communications network, each of the endpoints in the set being assigned a different communications channel over which the endpoint communicates;   a substation processing unit coupled to the set of endpoints, the substation processing unit including one or more processors configured to interact with the set of endpoints and further configured to:
 receive a symbol over a particular communications channel; 
 decrypt the symbol using a decryption key that is assigned to a particular endpoint that has been assigned to communicate over the particular communications channel; 
 determine that the symbol was transmitted by the particular endpoint, the determination being made based on a measure of error for the decrypted symbol not exceeding a threshold error measure; and 
 in response to determining that the symbol was transmitted by the particular endpoint, logging the decrypted symbol as a valid symbol. 
   
     
     
         13 . A system comprising:
 a set of endpoints in a communications network, each of the endpoints in the set being assigned a different communications channel over which the endpoint communicates;   a substation processing unit coupled to the set of endpoints, the substation processing unit including one or more processors configured to interact with the set of endpoints and further configured to:
 receive a symbol over a particular communications channel; 
 decrypt the symbol using a decryption key that is assigned to a particular endpoint that is assigned the particular communications channel; 
 compute a measure of error for the decrypted symbol; 
 determine whether the measure of error exceeds a threshold error measure; 
 in response to determining that the measure of error exceeds the threshold error measure, identify the decrypted symbol as a symbol from a different endpoint; and 
 in response to determining that the measure of error does not exceed the threshold error measure:
 identify the decrypted symbol as a valid symbol transmitted by the particular endpoint; and 
 log the valid symbol. 
 
   
     
     
         14 . The system of  claim 13 , wherein at least one of the endpoints is further configured to:
 generate the symbol to include payload data and error correction data;   encrypt the symbol using an encryption key that is assigned to the particular endpoint; and   transmit the encrypted symbol over the particular communications channel.   
     
     
         15 . The system of  claim 14 , wherein the at least one endpoint is further configured to:
 insert an error correcting code into the payload data; and   encrypt the symbol following insertion of the error correcting code.   
     
     
         16 . The system of  claim 13 , wherein the substation processing unit is further configured to:
 receive a plurality of different symbols over a plurality of different communications channels, each different communications channel being assigned to a different endpoint; and   for each of the different communications channels, decrypt the symbol received over the communications channel using a decryption key that is assigned to the endpoint to which the communications channel is assigned.   
     
     
         17 . The system of  claim 16 , wherein the substation processing unit is further configured to retrieve, for each different endpoint, a different decryption key that is assigned to the different endpoint. 
     
     
         18 . The system of  claim 13 , wherein the substation processing unit is further configured to:
 compute a bit error rate for the decrypted symbol; and   determine whether the bit error rate exceeds a threshold bit error rate.   
     
     
         19 . The system of  claim 13 , wherein the set of endpoints are a set of meters in a power line communications network. 
     
     
         20 . The system of  claim 13 , wherein the substation processing unit is further configured to iteratively decrypt the received symbol using different decryption keys and determine that the symbol is from a particular endpoint based on the decryption key for which the decrypted symbol has a lowest measure of error for the symbol.