Two round Cs marked on the front door constitute and replace the host's message to the visitor friend: semicircles, not 'Ci', are = if you are looking for me I'm not there! The time it takes to solve the encrypted mystery will allow the two friends to find each other again. It is the mechanism, one among many, that characterizes "pure cryptography" referred to simply as "cryptography"; the example cited is certainly not very orthodox, but it gives the idea of the absolute freedom of reasoning to be followed in the explanation of this type of game: the solver is given no other help than the numerical indication of the letters that make up the words of the first reading (key) and the decisive sentence.
From this example of Cameo of 1924,
Encryption (1,1,3,3,1,1,1,8,1,1, = 2,6,1,3,2,7)
it is possible to draw the solution: A fan ale to G, to the left of A = a gas light in the street. It seems impossible, but not so much, if it is true that every month the specialized magazines publish dozens of these puzzles and they are systematically solved!
Their difficulty derives mainly from the variety of mechanisms on which the decisive key can hinge: which, in fact, can concern the rejection, addition, displacement of one or more letters, their anomalous positioning or graphic representation, different reading offered by the set of letters exposed, on the finalized replacement of some letters, etc.
CANUTI CA, if you lose N, U, T, I = houses for prisoners
ROPE TESA ROPE stands with TESA = fatal dispute
.OR.GGIO CA give you courage = anchor cables
SAW with GA stocks S, E = rude colleague
FONF, O, N spaced = allocated funds
GELSO S removed, GELO yes à = foolish jealousy
CONCA CONTE, if for CA we will use TE = disputes for remote causes
… PQGST… G where R is not evident = Nepalese government
MICI if you forget MI, CI = chemical sediments
all are quite significant examples of "pure cryptographs".
An essential help offered to the solver is given by the numerical diagram which informs about the number of letters of the words of the first and second reading, as shown in these examples:
Encryption (2,1,1,8 = 6,6):
Encryption (1,1,6,1,1,1,4 = 2,6,3,4)
which are explained respectively as follows:
the GA reply = tie parcels
the rising, FROM the sun = the rising of the sun