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G. Purdy, 1974 paper in The Communications of the ACM , .A High Security Login Procedure.

Abstract

The author introduces a lacunary (Purdy) polynomial P(x) of degree d ~ 10^50 modulo a prime p ~ 10^200. The original purpose of P(x) was to protect passwords on the Arpanet. ( Google .Purdy Polynomial. for description of its use in the VAX VMS system of DEC) but it has been used way beyond this, particularly in the defense industry and in (proprietary) software protection. A top secret clearance would be required to learn the details of its use in defense. Suffice it to say that its extremely high security makes it suitable for protecting the codes that are used to arm nuclear weapons in missiles and bombers.