"The one-time pad (OTP) is an encryption technique that cannot be cracked, but requires the use of a one-time pre-shared key the same size as, or longer than, the message being sent. In this technique, a plaintext is paired with a random secret key (also referred to as a one-time pad). Then, each bit or character of the plaintext is encrypted by combining it with the corresponding bit or character from the pad. "
XOTP is an implementation of this, written in C, that uses bitwise Exclusive-OR (XOR) to combine the bytes of the plaintext with those of the key, hence the name.
As XOTP itself will tell you :
-> xotp <command : e or d> [(optional) option] [(optional) option's argument] ...
Options :
1. "-f" : Give input file.
Without "-f", input is read from stdin.
2. "-p" : Give pad file.
2.1 : If encrypting : if the pad file exists, it is read as the pad.
If not, the generated pad is saved to it.
Without "-p" , pad is saved to the input file (if specified) with a ".pad" extension.
Otherwise, it is saved to "pad.pad"
2.2 : If decrypting : the pad file is read to decrypt the input.
Without "-p", if "-f" is supplied, pad is read from stdin.
3. "-o" : Give output file.
Without "-o", output is written to stdout.
The idea behind arguments to XOTP is "control by implication". Explicit commands are also possible; the idea is to equip the user to imply more than he types.
So, invocations can be as small as xotp e . This implies that xotp will read from stdin , which it will encrypt by generating a pad of appropriate size saved to pad.pad (in the cwd) , and the encrypted data will be written to stdout.
Or, invokations can be as verbose as xotp e -f foo -p pad -o bar. Here, "foo" will be encrypted to "bar", with the pad "pad". If "pad" already exists, XOTP attempts to read it as the pad, if it does not, it generates a pad and saves it to "pad".
However, it is still kept simple : there are only 3 options , they can occur in any order, most of them are optional.