$ include "seed7_05.s7i";
  include "bigint.s7i";
  include "bytedata.s7i";

const proc: main is func
  local
    const string: plainText is "Rosetta Code";
    # Use a key big enough to hold 16 bytes of plain text in a single block.
    const bigInteger: modulus is 9516311845790656153499716760847001433441357_;
    const bigInteger: encode is 65537_;
    const bigInteger: decode is 5617843187844953170308463622230283376298685_;
    var bigInteger: plainTextNumber is 0_;
    var bigInteger: encodedNumber is 0_;
    var bigInteger: decodedNumber is 0_;
    var string: decodedText is "";
  begin
    writeln("Plain text:             " <& plainText);
    plainTextNumber := bytes2BigInt(plainText, UNSIGNED, BE);
    if plainTextNumber >= modulus then
      writeln("Plain text message too long");
    else
      writeln("Plain text as a number: " <& plainTextNumber);
      encodedNumber := modPow(plainTextNumber, encode, modulus);
      writeln("Encoded:                " <& encodedNumber);
      decodedNumber := modPow(encodedNumber, decode, modulus);
      writeln("Decoded:                " <& decodedNumber);
      decodedText := bytes(decodedNumber, UNSIGNED, BE);
      writeln("Decoded number as text: " <& decodedText);
    end if;
  end func;