As the name says, a one-time pad is a key to be used for encryption only once. It is a random chain of characters and must have at least the same length like the plaintext to be encrypted.

The creation of true randomness for a key would require some truly random process like using radioactive emissions to produce a chain of characters. Secret services may have those means at hand, that are certainly not available to average people.

But you can take some precautions, like avoiding the use of any known plaintext words. If you want to share a key with another person, you could e.g. agree on a specific text passage/page in a book that both of you own, and use the second character of every line or word as a key. While a key generated with this method is not unbreakable like a really random key, it will help against attacks, where libraries of known words are tried as parts of the key. You are encouraged to develop your own ideas of secret-key-generation – and keep them your secret! IMPORTANT: NEVER USE A ONE-TIME PAD TWICE! If an attacker gets hold of two encrypted texts that have been encrypted with the same key, it will be easy to figure out the key!

The intelligent text field will filter out any numbers and special characters. Actually only the 26 characters of the alphabet “ABCDEFGHIJKLMNOPQRSTUVWXYZ” will be used for encryption. So make sure, not to use any special characters or numbers, that are a relevant content of your text. For numbers use words – e.g. instead of “7” write “SEVEN”. You may write or paste any kind of text, just don’t forget to replace the numbers with words, if they are relevant to your message, otherwise, you don’t have to care about special characters or numbers in the pasted text, as they will be removed automatically – this will help to make encryption safer, as the content of an encrypted text may not be inferred e.g. by the position of a period, comma, etc. Also lowercase characters will be changed to uppercase automatically and the characters will be grouped (e.g. by using a space after every 5 characters). Character grouping helps against an attacker who tries to infer content by looking at the word lengths of an encrypted text.

Different colors help you to differentiate between PLAINTEXT (BLUE), the ONE-TIME PAD (RED) and the ENCRYPTED TEXT (GREEN). So you always know, which kind of information you should input into a text field – on the other hand it lets you easily identify the kind of information that you look at on the output page.

SimplePrivacy stores your plaintext locally only as long as you are using the app and for the time that you put the app into the background, e.g. because you use another app temporarily. When you are done encrypting or decrypting texts, always make sure to fully close the SimplePrivacy app the usual way by swiping the app preview upwards on your home screen.

To protect you from accidentally reusing your one-time pad (key), SimplePrivacy will delete all texts and keys the moment you start another encryption or decryption.

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