Help with Activities
Most ciphers that are discussed are accompanied by a flash activity that you can use to encrypt/decrypt messages. Each is slightly different, depending on the cipher, but the main ideas are explained on this page.
All activities have two input areas. One for plaintext and one for ciphertext. If you are trying to encrypt a message, then type the plaintext into the plaintext box. If you are trying to decrypt, type the ciphertext in the ciphertext box. Next to each of these is the respective button to perform the encryption/decryption.
Most ciphers work with a variety of alphabets, and if this is the case, then this is shown at the top of the activity. You can select one of the four most commonly used alphabets, or you can type in your own, including any characters you like. Just make sure that both the encryption and decryption use the same alphabet (with characters in the same order).
Most ciphers also have a key of some form. This can take many forms, but it will be near the top of the activity, and should be clear if you have read the relevant information on the cipher first.
"Slow Encrypt" and "Slow Decrypt" are functions to encrypt/decrypt one letter at a time. This function is really useful if you are using this in a classroom, and are getting students to check their method as they go.
It is commonplace when enciphering a message to remove all the characters not in the alphabet chosen. In particular, if using the normal alphabet of 26 letters, then this removes all punctuation and spaces. This is useful to make it harder to break the cipher, as it is not clear where words and sentences start.
Further to this, since the invention of the telegraph, it has also become normal to split the ciphertext in to blocks of 5 characters, by inserting a space between each block. This made it easier to transmit the ciphertext accurately, but also has the benefit of removing recognisable word patterns (eg you cannot spot one letter words).
For many ciphers, there is also a button to generate the ciphertext alphabet, which has been used to produce the encryption, usually generated from the key in some way. This will be different for the various types of ciphers, but should be clear what is meant if you have read the accompanying information on the page about the cipher.