convert to 5.0.0 from 1.0 ?

[amervelic]

 static Encrypter encryptorSalsa20 = Encrypter(Salsa20(key, iv));
 static final key = '12345678123456781234567812345678';
 static String iv = 'jXn2r5u8'; 

static String encryptTextSalsa20(String text) {

   String base64Text = base64.encode(utf8.encode(text));
   String encText = encryptorSalsa20.encrypt(base64Text);
   return encText;
 }

 static String decryptTextSalsa20(String text) {
   var decStr = utf8.decode(base64.decode(encryptorSalsa20.decrypt(text)));
   return decStr;
 }