Secret Key Cryptography

9 Fractionation

This chapter covers

• The Polybius square
• Splitting a letter into smaller parts, such as bits or hexadecimal digits
• Mixing and recombining those parts

The first two basic tools of cryptography are substitution and transposition, which are covered in chapters 5 through 8. The third fundamental element of cryptography is fractionation. This means breaking the normal units of language, letters, syllables and words into smaller units and operating on those units. The smaller units are commonly bits, decimal digits, hexadecimal digits, or digits in other number bases. This chapter covers fractionation using digits in bases 2, 3, 5, 6, and 16, plus some other forms of fractionation.

9.1 Polybius square

Possibly the oldest method for ...