The Vernam encryption algorithm works with an exclusive-OR logical operation (compare binary XOR encryption). However, since encryption by means of an exclusive-OR is relatively easy to break with a short key, a document is used here as the key. XOR encryption is (provably) secure if a key (or a key file) which contains random bits and is at least as long as the document to be encrypted is chosen (this is known as a one-time pad).
To invoke this function, select the menu Crypt/Decrypt \ Symmetric (classic) \ Vernam: Then a dialog opens in which the file with the key (keystream) can be selected.
An example of the Vernam encryption algorithm can be found in the Examples chapter.
Remark 1:
This implementation does not check, whether the data of the key file is random
or whether the data of the key file is longer than the cleartext document.
Remark 2:
If the data of the cleartext document is longer than the keystream, then the
key automatically is applied cyclically (repeated again and again).
Remark 3:
The character "A" in the keystream file for Vernam has the same effect on the
cleartext document as the two hex numbers "41" for XOR.