Now, we can use the encryption cipher: Cipher encryptCipher = Cipher.getInstance("RSA") īyte encryptedFileBytes = encryptCipher.doFinal(fileBytes) Īnd finally, we can overwrite it with new, encrypted content: try (FileOutputStream stream = new FileOutputStream(tempFile. Working With Filesīyte fileBytes = Files.readAllBytes(tempFile) String decryptedMessage = new String(decryptedMessageBytes, StandardCharsets.UTF_8) įinally, let’s verify if the encryption-decryption process went correctly: assertEquals(secretMessage, decryptedMessage) 5. We’ll invoke the cipher as previously with the doFinal method: byte decryptedMessageBytes = decryptCipher.doFinal(encryptedMessageBytes) I have the program set up so that it asks the user for either Encryption/Decryption, then the message that they want to. This time we’ll initialize it with a decryption mode and a private key: Cipher decryptCipher = Cipher.getInstance("RSA") ĭecryptCipher.init(Cipher.DECRYPT_MODE, privateKey) The purpose of the program is to decode/encode to a type of code called Caesar Shift, which basically just takes each letter of a word/sentence and shifts it to the right by a 'shift key'. For this, we’ll need another Cipher instance. It initially creates a key-table of 55 matrix. The only difference is that it encrypts a digraph (a pair of two letters) instead of a single letter. Now, let’s see how we can decrypt the message to its original form. Playfair cipher is an encryption algorithm to encrypt or encode a message. This way, the message will be more readable and easier to work with. The first line of input contains K K ( K. For example, when K 3 K 3, ZOOM is encoded as FXAB: The challenge is to write a decoder. If we’d like to store it in a database or send it via REST API, it would be more convenient to encode it with the Base64 Alphabet: String encodedMessage = Base64.getEncoder().encodeToString(encryptedMessageBytes) The encoding algorithm is a Caesar cipher with a shift ( S S) that depends on a parameter ( K K) and its position in the word ( P P, where P 1 P 1 for the first letter of each word): S 3 S 3, P + K P + K. (The other input key can be generated using the code snippet provided above). Now, our message is successfully encoded. However, with all that knowledge, if we still end up in a situation where the sensitive information to be encrypted is in a String, we first need to convert it into a byte array and invoke the encrypt and decrypt functions introduced above. Decode Basic Base 64 format to String byte actualByte Base64.getDecoder (). Note that it accepts only byte array arguments, so we need to transform our string before: byte secretMessageBytes = secretMessage.getBytes(StandardCharsets.UTF_8) )īyte encryptedMessageBytes = encryptCipher.doFinal(secretMessageBytes) Explanation: In above code we called Base64.Encoder using getEncoder () and then get the encoded string by passing the byte value of actualString in encodeToString () method as parameter. Having that ready, we can invoke the doFinal method to encrypt our message. Cipher encryptCipher = Cipher.getInstance("RSA") ĮncryptCipher.init(Cipher.ENCRYPT_MODE, publicKey)
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