Java - rsa example
https://stackoverflow.com/questions/13990181/rsa-2048-encryption-decryption-exception
https://stackoverflow.com/questions/12471999/rsa-encryption-decryption-in-android
https://stackoverflow.com/questions/24338108/java-encrypt-string-with-existing-public-key-file
https://three-father-programming.tistory.com/11