Can we consider the Scytale a block cipher ? If yes why ? Can you tell me ?
Obviously no. Here are the reasons;
The Scytale is a transposition cipher that just changes the order of the plaintext, i.e. a permutation on the positions. One might consider the diameter of the rod as the block size but it is not. The block size can be considered as the length of the message parchment when wrapped around the rod. That is not fixed, it must go as long as the message size and one cannot divide the message into blocks. Whereas, in block ciphers, we have a fixed block size and to encrypt we need mode of operation.
Also, all block ciphers operate on bits not in characters. Scytale operates on characters like almost all classical ciphers. One can design a block cipher that operates on characters but that will be ridiculous.
The key size (space) of Scytale is limited and related to the message. The possible key sizes cannot exceed the message size - and some rods can have unpractical diameters. In block ciphers, the key is not related to the message space, independent from it. The key selected randomly from the key-space that has no relation to the message space.