Abstract: A multiply unit includes an extended precision accumulator. Microprocessor instructions are provided for manipulating portions of the extended precision accumulator including an instruction to move the contents of a portion of the extended accumulator to a general-purpose register (“MFLHXU”) and an instruction to move the contents of a general-purpose register to a portion of the extended accumulator (“MTLHX”).

Abstract: An operational instruction (Adrm) of the data reading, writing or modification type, or transaction, in a ROM memory (ME) of a microcontroller (CP) may be attacked by a command (COM) from a EEPROM memory (MC) of the microcontroller in order to access a secret data item (DS) instead of a public data item (CB), in response to an end instruction (Adr(m+3)). A test (Adr(m+1)) is immediately executed following an operational instruction (Adrm) in order to protect the latter. The test condition such as comparison is related to at least one operand (DPTR) of the said operational instruction. The result (CB) of the operational instruction is transferred to the EEPROM memory only when the condition is satisfied.

Abstract: A multiply unit includes an extended precision accumulator. Microprocessor instructions are provided for manipulating portions of the extended precision accumulator including an instruction to move the contents of a portion of the extended accumulator to a general-purpose register (“MFLHXU”) and an instruction to move the contents of a general-purpose register to a portion of the extended accumulator (“MTLHX”).

Abstract: Polynomial arithmetic instructions are provided in an instruction set architecture (ISA). A multiply-add-polynomial (MADDP) instruction and a multiply-polynomial (MULTP) instruction are provided.

Abstract: A method relating to probabilistic digital signatures of a message, between a signatory and a checker, uses an algorithm based on the calculation of a discrete logarithm. For the signatory, at least two signatures are generated for the same unchopped message, these signatures being calculated by the algorithm by means of the same public and private key parameters using respectively distinct random values. For the checker, all the signatures of the message are checked.

Abstract: A method for generating electronic keys from two integer numbers a, b, includes the step of verifying that the numbers are prime relative to each other. This verification step comprises the operations of calculating the modular exponentiation a&lgr;(b)modb, where &lgr; is the Carmichael function, verifying that this modular exponentiation is equal to 1, storing the pair a, b when equality is verified, and reiterating the procedure with another pair when there is no verification. The invention applies to chip cards with a microprocessor having an arithmetic processor.