mobile1(gctf)
下载下来是个apk
jadk打开查看源码
有两个关键方法
代码语言：javascript复制public static void main(String[] args){
TestActivity TestActivity=new TestActivity();
System.out.println(String.valueOf(TestActivity.checkSN(“Tenshine”,“Tenshine”)));
}
private boolean checkSN(String userName, String sn) {
if (userName == null) {
return false;
}
try {
// if (userName.length() == 0 || sn == null || sn.length() != 22) {
// return true;
// }
MessageDigest digest = MessageDigest.getInstance(“MD5”);
digest.reset();
digest.update(userName.getBytes());
String hexstr = toHexString(digest.digest(), “”);
StringBuilder sb = new StringBuilder();
for (int i = 0; i < hexstr.length(); i = 2) {
sb.append(hexstr.charAt(i));
}
System.out.println(“flag{“ sb.toString() “}”);
if ((“flag{“ sb.toString() “}”).equalsIgnoreCase(sn)) {
return true;
}
return false;
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
return false;
}
}
private static String toHexString(byte[] bytes, String separator) {
StringBuilder hexString = new StringBuilder();
for (byte b : bytes) {
String hex = Integer.toHexString(b & 255);
if (hex.length() == 1) {
hexString.append(‘0’);
}
hexString.append(hex).append(separator);
}
return hexString.toString();
}运行输出
获得flag
flag{bc72f242a6af3857}
false
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