凯撒密码暴力解码方法Java实现

凯撒密码最简单粗暴的解码方式：遍历所有可能的移位方法然后输出。在本实验中，确保输入字符仅包含大写小写和空格.

public class question {
    public static void main(String[] args) {
        System.out.println("输入：");
        Scanner scan = new Scanner(System.in);
        String s = scan.nextLine();
        for(int k = 1; k < 26; k ++ ) {
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) == ' ') {
                    sb.append(' ');
                    continue;
                } else {
                    if (s.charAt(i) >= 'A' && s.charAt(i) <= 'Z') {
                        if ((int) (s.charAt(i)) + k > 90) {
                            sb.append((char) (s.charAt(i) + k - 90 + 64));
                        } else {
                            sb.append((char) (s.charAt(i) + k));
                        }
                    } else {
                        if ((int) (s.charAt(i)) + k > 122) {
                            sb.append((char) (s.charAt(i) + k - 122 + 96));
                        } else {
                            sb.append((char) (s.charAt(i) + k));
                        }
                    }
                }
            }
            System.out.println("k = " + k  + " Result : " + sb.toString());
        }
    }
}

测试案例：Rjjy rj ts ymj xfggfym bj bnqq inxhzxx ymj uqfs

结果：

输入：
Rjjy rj ts ymj xfggfym bj bnqq inxhzxx ymj uqfs
k = 1 Result : Skkz sk ut znk yghhgzn ck corr joyiayy znk vrgt
k = 2 Result : Tlla tl vu aol zhiihao dl dpss kpzjbzz aol wshu
k = 3 Result : Ummb um wv bpm aijjibp em eqtt lqakcaa bpm xtiv
k = 4 Result : Vnnc vn xw cqn bjkkjcq fn fruu mrbldbb cqn yujw
k = 5 Result : Wood wo yx dro ckllkdr go gsvv nscmecc dro zvkx
k = 6 Result : Xppe xp zy esp dlmmles hp htww otdnfdd esp awly
k = 7 Result : Yqqf yq az ftq emnnmft iq iuxx pueogee ftq bxmz
k = 8 Result : Zrrg zr ba gur fnoongu jr jvyy qvfphff gur cyna
k = 9 Result : Assh as cb hvs goppohv ks kwzz rwgqigg hvs dzob
k = 10 Result : Btti bt dc iwt hpqqpiw lt lxaa sxhrjhh iwt eapc
k = 11 Result : Cuuj cu ed jxu iqrrqjx mu mybb tyiskii jxu fbqd
k = 12 Result : Dvvk dv fe kyv jrssrky nv nzcc uzjtljj kyv gcre
k = 13 Result : Ewwl ew gf lzw ksttslz ow oadd vakumkk lzw hdsf
k = 14 Result : Fxxm fx hg max ltuutma px pbee wblvnll max ietg
k = 15 Result : Gyyn gy ih nby muvvunb qy qcff xcmwomm nby jfuh
k = 16 Result : Hzzo hz ji ocz nvwwvoc rz rdgg ydnxpnn ocz kgvi
k = 17 Result : Iaap ia kj pda owxxwpd sa sehh zeoyqoo pda lhwj
k = 18 Result : Jbbq jb lk qeb pxyyxqe tb tfii afpzrpp qeb mixk
k = 19 Result : Kccr kc ml rfc qyzzyrf uc ugjj bgqasqq rfc njyl
k = 20 Result : Ldds ld nm sgd rzaazsg vd vhkk chrbtrr sgd okzm
k = 21 Result : Meet me on the sabbath we will discuss the plan
k = 22 Result : Nffu nf po uif tbccbui xf xjmm ejtdvtt uif qmbo
k = 23 Result : Oggv og qp vjg ucddcvj yg yknn fkuewuu vjg rncp
k = 24 Result : Phhw ph rq wkh vdeedwk zh zloo glvfxvv wkh sodq
k = 25 Result : Qiix qi sr xli weffexl ai ampp hmwgyww xli tper

所以答案很明显在k = 21出现。
Meet me on the sabbath we will discuss the plan.

这个问题同样可以根据词频和英语用法习惯猜测。注意到ymj的两次出现。英文可以想到the，代入检验即可。

或者从两个词的地方入手，猜测：at/on/or…