Apart from using SecureString & EncryptedString, we can also use EncryptionService object which provides an easy-to-use optionby which you can create a one-time key to encrypt and decrypt plain text.
var key = EncryptionService.generateOneTimeKey();
System.log(key); //G75Ypi8PHD0zYeiXQ32PiA==
var encryptedString = EncryptionService.encrypt("abcd1234",key);
System.log(encryptedString); //vro:enc:v1:pzqwDVjvz4h7Qg8uEJNq/IKfXyCz7S+ht72sHLMvztlX4Geh
var decryptedString = EncryptionService.decrypt(encryptedString,key);
System.log(decryptedString); //abcd1234
