Cryptographic authentication of transmitted messages using pseudorandom numbers

A method of cryptographically synchronizing a command transmitting unit with a command performing receiving module for selective response thereto, comprising:

• providing, in both said transmitting unit and in said receiving module, a word including a key portion derived at least in part from a secret initial value;
• in said transmitting unit:
• performing an encryption operation on said word to provide an encrypted word;
• and
• transmitting a command word derived at least in part from said encrypted word and indicative of a synchronization command;
• comprising in said receiving module:
• receiving said command word;
• recovering said encrypted word from said received command word;
• performing a decryption operation on said recovered encrypted word to recover said word;
• comparing the key portion of said word with the key portion of said recovered word;
• and
• providing cryptographic synchronization between said receiving module and said transmitting unit only if the key portion of said word is identical to the key portion of said recovered word.

A method of transferring a cryptographically authenticated command from a transmitting unit to a receiving module, comprising:

• providing, in both said transmitting unit and in said receiving module, a code word, derived from a secret initial value, including a key portion and a command portion;
• comprising, in said transmitting unit:
• providing a plurality of bits indicative of a command to be transmitted;
• exclusive ORing said plurality of bits into corresponding bits of said command portion to provide an altered word;
• performing an encryption operation on a word including said altered word to provide an encrypted word;
• and
• transmitting a command word derived at least in part from said encrypted word;
• comprising in said receiving module:
• receiving said command word;
• recovering said encrypted word from said received command word;
• performing a decryption operation on said recovered encrypted word to recover said altered word;
• and
• exclusive ORing the command portion of said code word with the command portion of said recovered altered word to recover said plurality of bits.

A cryptographically authenticated control system in which a command message from a transmitting unit causes a physical effect in a receiving module;

• said transmitting unit comprising:
• a source of signals for providing a seed signal indicative of a secret initial value, said initial value being essentially unique to said transmitting unit;
• command switches that indicate a physical effect to be caused by said receiving module;
• and
• first signal processing means responsive to selected operation of said switches indicative of a command for providing a random signal indicative of a variable random number, for providing a combined number including a key word derived from said secret initial value concatenated with the random number defined by said random signal, for encrypting said combined number, and for transmitting, to said receiving module, a command word signal having a key portion derived from the encrypted combined number and including an indication of said command;
• said receiving module comprising:
• a signal source for providing a seed signal indicative of said secret initial value;
• and
• second signal processing means for receiving said command word signal, for recovering said encrypted combined number from said key portion of said received command word signal, for decrypting said recovered encrypted combined number so as to recover said combined number, for providing a key word derived from said secret initial value, for comparing said key word with an equivalent portion of said recovered combined number, for storing, in response to said initial value being identical to said equivalent portion, the random number portion of said recovered combined word for subsequent use, and for comparing said random number portion, for which said equivalent portion is equal to said key word, with a similar random number portion, previously stored for subsequent use in response to a prior key word comparison, and for selectively performing the command indicated by said command word only if said compared random number portions are not equal.

A method of causing an alarm at a receiving module in response to a command from a transmitting unit, comprising:

• providing, in both said transmitting unit and in said receiving module, a word including a key portion derived at least in part from a secret initial value;
• in said transmitting unit:
• performing an encryption operation on said word to provide an encrypted word;
• and
• transmitting a command word derived at least in part from said encrypted word and indicative of an alarm command;
• comprising in said receiving module:
• receiving said command word;
• recovering said encrypted word from said received command word;
• performing a decryption operation on said recovered encrypted word so as to recover said word;
• comparing the key portion of said word with the key portion of said recovered word;
• and
• setting off an alarm near said receiving module if the key portion of said word is identical to the key portion of said recovered word.