Systems (100) and methods (700) for customizing a cryptographic algorithm. The methods comprise: providing an electronic device with the cryptographic algorithm implementing a permutation function ƒ configured to produce a first keystream using bits input thereto, the permutation function ƒ comprising a round function ƒround consisting of a mixing layer in which input bits are combined together; and customizing the mixing layer of the permutation function ƒ while the electronic device is in the field. The mixing layer is customized by: receiving, by the electronic device, a first user-software interaction for entering a first bit string comprising a plurality of first arbitrary bits; breaking the first bit string into a plurality of equal length segments each comprising only a portion of the plurality of first bits; and translating each of the equal length segments into irreducible polynomial coefficients and/or an irreducible polynomial identifier.