A method for instruction processing may include adding a first operand from a first register, a second operand from a second register and a carry input bit to generate a sum and a carry out bit, loading the sum into a third register and loading the carry out bit into a most significant bit position of the third register to generate a third operand, performing a single bit shift on the third operand via a shifter unit to produce a shifted operand and loading the shifted operand into the fourth register, loading a least significant bit from the sum into the most significant bit position of the fourth register to generate a fourth operand, generating a greatest common divisor (GCD) of the first and second operands via the fourth operand and generating a public key based on, at least in part, the GCD. Many alternatives, variations and modifications are possible.