Replacing String in the original String only

During my program I am allowing a user to input a string. But then it also replaces the things in the output, so all I want it to do is replace in the original string. Thank you.

public class Crypto {
    public Crypto() {
        String s = f;
    }

    public String encrypt(String s) {

        String myString = s.replace("v", "ag\'r").replace("V", "ag\'r")
                .replace("m", "ssad").replace("M", "ssad")
                .replace("g", "jeb..w").replace("G", "jeb..w")
                .replace("b", "dug?/").replace("B", "dug?/");
        return myString;
    }

    public String decrypt(String d) {
        String myString = d.replace("ag‘,r", "v").replace("ssad", "m")
                .replace("jeb..w", "g").replace("dug>?/", "b");
        return myString;
    }

    public String d;
    public String s;
    public String f;
    public String myString;
}