TheCodeBreakers
cryptography, on the other hand, do not conceal the presence of a secret message but render it
unintelligible to outsiders by various transformations of the plaintext.
Two basic transformations exist. In transposition, the letters of the plaintext are jumbled; their normal
order is disarranged. To shuffle secret into ETCRSE is a transposition. In substitution, the letters of the
plaintext are replaced by other letters, or by numbers or symbols. Thus secret might become 19 5 3 18 5 20,
or XIWOXY in a more complicated system. In transposition, the letters retain their identities— the two e's of
secret are still present in ETCRSE—but they lose their positions, while in substitution the letters retain their
positions but lose their identities. Transposition and substitution may be combined.
Substitution systems are much more diverse and important than transposition systems. They rest on the
concept of the cipher alphabet
annaabi.ee 
