找到关键代码在mainactivity中.
输入处理:
关键比较:
需要a类中的字符串数组C要等同于a方法对v7_1处理的结果.
查看A类a方法, 可以看到是根据a.b[v6]进行hash加密, 任选了一个进行爆破, 爆不出来. 仔细翻了翻了, 前面的welcomeactivity类更改了a密钥byte数组和b数组.
对密钥进行MD5.
当b数组的值<8时, 不使用密钥, hash加密的方式不同, b数组>=8时, 相同的hash加密HmacSha512, 不同密钥.
这样就直接开始爆破, 8组数据, 范围为4个0-0x7f字节.直接抄程序反编译代码去爆破
HmacSha512: 将密钥和密文对应就行
无密钥hash: 将hash方法和密文对应
这里我没有再去考虑大于7F的输入, 我直接分析flag的输出:
这里可以看到, 如果使用了HmacSha512, 需要反序.
最后爆破了半天得到flag.
输入处理:
输入为32字节, 然后依次查询a类的a数组再输入中的位置, 将位置+32后转化为2进制去掉首位保存字符串.
保存的范围就是00000 - 11111, 一共是16个.
查看a类的a数组, 可以编写脚本处理发现只有32种. 要求的是每个数都再输入中能找到, 不能重复.
之后就是2进制连起来, 依次取8位, 转化为byte数组.
密文的生成直接抄反编译代码, 然后调试可以发现, 是圆周率. 长度是360位.
校验:
要求的是依次取圆周率字符串2位, 视为10进制数和5位2进制数生成的byte数组一一比较, 一共180次.
这里不妨算一下, a数组的长度为288位, 转化出来的2进制长度为288 5 == 1440, 密文长度是180 8 == 1440, 刚好对应.
加上flag{}就ok.
附件中的HAHAHAHA我重新打包过
byte[] v7_1 = a.c(v1_1[v6]);
....
while(v9 < v7_1.length) {
v10 = v10 << 1 | (v7_1[v9] & 0x80) >>> v2;
v7_1[v9] = ((byte)(v7_1[v9] & 0x7F));
++v9;
}
byte[] v7_1 = a.c(v1_1[v6]);
....
while(v9 < v7_1.length) {
v10 = v10 << 1 | (v7_1[v9] & 0x80) >>> v2;
v7_1[v9] = ((byte)(v7_1[v9] & 0x7F));
++v9;
}
String v9_1 = a.a(v10, v7_1);
if(v9_1 != null && (v9_1.equals(a.a(a.b[v6], v7_1)))) {
if(!v9_1.equals(a.c[v6])) {
}
else {
++v6;
continue;
}
}
String v9_1 = a.a(v10, v7_1);
if(v9_1 != null && (v9_1.equals(a.a(a.b[v6], v7_1)))) {
if(!v9_1.equals(a.c[v6])) {
}
else {
++v6;
continue;
}
}
for(v0 = 0; true; ++v0) {
int[] v1 = a.b;
if(v0 >= v1.length) {
break;
}
v1[v0] ^= 0xAB;
}
....
while(v4 < a.a.length) {
try {
v0_1 = MessageDigest.getInstance("MD5");
}
catch(NoSuchAlgorithmException v1_1) {
v1_1.printStackTrace();
}
v0_1.update(a.a[v4]);
a.a[v4] = v0_1.digest();
++v4;
}
for(v0 = 0; true; ++v0) {
int[] v1 = a.b;
if(v0 >= v1.length) {
break;
}
v1[v0] ^= 0xAB;
}
....
while(v4 < a.a.length) {
try {
v0_1 = MessageDigest.getInstance("MD5");
}
catch(NoSuchAlgorithmException v1_1) {
v1_1.printStackTrace();
}
v0_1.update(a.a[v4]);
a.a[v4] = v0_1.digest();
++v4;
}
import java.nio.charset.StandardCharsets;
import java.math.BigInteger;
import java.security.GeneralSecurityException;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
public class demo {
public static final String v0 = "HmacSha512";
public static void main(String[] args) {
MessageDigest v0_1 = null;
StringBuilder v1_2;
byte[] miwen = new byte[4];
String v6_1 = "%02x";
try {
for (int i=0x0; i<=0x7e; i++) {
miwen[0] = (byte)i;
for (int j = 0x0; j <= 0x7e; j++) {
miwen[1] = (byte)j;
for (int k = 0x0; k <= 0x7e; k++) {
miwen[2] = (byte)k;
for (int l = 0x0; l <= 0x7e; l++) {
miwen[3] = (byte)l;
try {
v0_1 = MessageDigest.getInstance("MD5");
}
catch(NoSuchAlgorithmException v1_1) {
v1_1.printStackTrace();
}
byte[] tmp = "ALFjcgztxnUaC89v".getBytes();
v0_1.update(tmp);
byte[] miwen2 = v0_1.digest();
SecretKeySpec v1 = new SecretKeySpec(miwen2, v0);
Mac v3 = Mac.getInstance(v0);
v3.init(((Key)v1));
v3.update(miwen);
String v2_2;
String s = "78b0be39e63b6837";
for(v2_2 = new BigInteger(1, v3.doFinal()).toString(16); v2_2.length() < 0x20; v2_2 = "0" + v2_2) {
}
if (v2_2.substring(0,16).equals(s)) {
System.out.printf("%x ", i);
System.out.printf("%x ", j);
System.out.printf("%x ", k);
System.out.printf("%x ", l);
System.out.printf("%n");
return;
}
}
}
}
}
}
catch(InvalidKeyException | NoSuchAlgorithmException v2) {
return;
}
}
}
import java.nio.charset.StandardCharsets;
import java.math.BigInteger;
import java.security.GeneralSecurityException;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
public class demo {
public static final String v0 = "HmacSha512";
public static void main(String[] args) {
MessageDigest v0_1 = null;
StringBuilder v1_2;
byte[] miwen = new byte[4];
String v6_1 = "%02x";
try {
for (int i=0x0; i<=0x7e; i++) {
miwen[0] = (byte)i;
for (int j = 0x0; j <= 0x7e; j++) {
miwen[1] = (byte)j;
for (int k = 0x0; k <= 0x7e; k++) {
miwen[2] = (byte)k;
for (int l = 0x0; l <= 0x7e; l++) {
miwen[3] = (byte)l;
try {
v0_1 = MessageDigest.getInstance("MD5");
}
catch(NoSuchAlgorithmException v1_1) {
v1_1.printStackTrace();
}
byte[] tmp = "ALFjcgztxnUaC89v".getBytes();
v0_1.update(tmp);
byte[] miwen2 = v0_1.digest();
SecretKeySpec v1 = new SecretKeySpec(miwen2, v0);
Mac v3 = Mac.getInstance(v0);
v3.init(((Key)v1));
v3.update(miwen);
String v2_2;
String s = "78b0be39e63b6837";
for(v2_2 = new BigInteger(1, v3.doFinal()).toString(16); v2_2.length() < 0x20; v2_2 = "0" + v2_2) {
}
if (v2_2.substring(0,16).equals(s)) {
System.out.printf("%x ", i);
System.out.printf("%x ", j);
System.out.printf("%x ", k);
System.out.printf("%x ", l);
System.out.printf("%n");
return;
}
}
}
}
}
}
catch(InvalidKeyException | NoSuchAlgorithmException v2) {
return;
}
}
}
import java.nio.charset.StandardCharsets;
import java.math.BigInteger;
import java.security.GeneralSecurityException;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
public class demo5 {
public static final String v0 = "HmacSha512";
public static void main(String[] args) {
MessageDigest v1_11;
byte[] miwen2;
byte[] miwen = new byte[4];
String v6_1 = "%02x";
StringBuilder v1_2;
for (int i=0x0; i<=0x7e; i++) {
miwen[0] = (byte)i;
for (int j = 0x0; j <= 0x7e; j++) {
miwen[1] = (byte)j;
for (int k = 0x0; k <= 0x7e; k++) {
miwen[2] = (byte)k;
for (int l = 0x0; l <= 0x7e; l++) {
miwen[3] = (byte)l;
String s = "f2dda5fc021fe2bf";
try {
v1_11 = MessageDigest.getInstance("SHA-384"
);
v1_11.update(miwen);
miwen2 = v1_11.digest();
v1_2 = new StringBuilder();
for(int v4 = 0; v4 < miwen2.length; ++v4) {
v1_2.append(String.format(v6_1, Byte.valueOf(miwen2[v4])));
}
String tmp = v1_2.toString().substring(0,16);
if (tmp.equals(s)){
System.out.printf("%x ", i);
System.out.printf("%x ", j);
System.out.printf("%x ", k);
System.out.printf("%x ", l);
System.out.printf("%n");
return;
}
}
catch(NoSuchAlgorithmException v0_2) {
v0_2.printStackTrace();
}
}
}
}
}
}
}
import java.nio.charset.StandardCharsets;
import java.math.BigInteger;
import java.security.GeneralSecurityException;
import java.security.InvalidKeyException;
import java.security.Key;
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最后于 2021-10-29 20:55
被margina1编辑
，原因：
