In this example of encryption and decryption a more complex shift has been used to encrypt text but the result is as susceptible to cryptanalysis as a one letter shift. The key has been derived from the title of a book and its author and the remaining letters have been allocated in sequence. Repeated letters in the name are ignored (EMMA becomes EMA, etc.).
It doesn't really matter how we define the key, it should still be a relatively easy matter to decrypt the message because only a substitution has been used. You could edit the code here to decrypt any single letter shift, it's just a matter of rearranging the letters.
Here is some encrypted text -
you can try to decrypt it or you can copy it and paste it into the
second window below.
Ng nf x gwhga hynkiwfxcco xpuyslcireir, gaxg x fnyeci bxy ny tsffiffnsy sd x essr dswghyi, bhfg zi ny lxyg sd x lndi. Aslikiw cnggci uysly gai diicnyef sw knilf sd fhpa x bxy bxo zi sy anf dnwfg iygiwnye x yineazshwassr, ganf gwhga nf fs licc dnmir ny
gai bnyrf sd gai fhwwshyrnye dxbncnif, gaxg ai nf psyfnriwir xf gai wneagdhc twstiwgo sd fsbi syi sw sgaiw sd gainw
rxheagiwf. Dwsb Twnri xyr Twijhrnpi Zo Jxyi Xhfgiy.
This form takes plain text, encrypts it and decrypts it.
The first window takes unencrypted text so you can write or paste any piece of text into it, encrypt it and check the decryption. Note that you can encrypt text more than once by copying it from the second box into the second; to decrypt such text you will have to copy it out of the third box into the second (don't think that encrypting more than once will make your text any harder to decrypt).