antilvl 1.4.0

it's been a while, but antilvl 1.4.0 is finally released. i did not plan to make another release, but there were some show-stopping bugs in the linux version and some other things that were just embarrassing. :D

major changes include:

• option to use your own signatures
• more control over which fingerprints are used
• support for verizon drm
• a few new anti-tampering checks are known
• some fixes in how fingerprints were applied

you can read more / download here: http://androidcracking.blogspot.com/p/antilvl_01.html

protection using checksums and key / unlocker apps

if an app requires an unlocker key app, it's likely there will be protection hidden in the key. perhaps the key performs a checksum on the main app, or the key stores pre-computed checksum values for the main app. this is easy to add if you're a developer and is somewhat tricky to handle as a cracker. the reason is the cracker must know how to calculate the checksums himself and inject those values into the app.

calculating checksums is a way to determine if your apk has been modified. there are at least four easy methods to do this. they are: md5, sha1, crc32 and adler32. once you run these guys on your apk you will have either a long number or a byte array. of course, you can't store the checksum in your main app since you wont know the checksum until the app is finished. for this reason, either the calculations or just the checksum values must be stored in another app signed by the same certificate, such as a key / unlocker app.

here's some example code of what the protection may look like in java:

// Copied directly and made private from R.java of Key App
// After creating strings..
private static final int tt_crc32=0x7f040002;
private static final int tt_md5=0x7f040004;

public static TestResult checkCRC32ChkSum() {
  // Get path to our apk on the system.
  String apkPath = Main.MyContext.getPackageCodePath();
  Long chksum = null;
  try {
    // Open the file and build a CRC32 checksum.
    // You could also use Adler32 in place of CRC32.
    FileInputStream fis = new FileInputStream(new File(apkPath));
    CRC32 chk = new CRC32();
    
    CheckedInputStream cis = new CheckedInputStream(fis, chk);
    byte[] buff = new byte[80];
    while ( cis.read(buff) >= 0 ) ;
    
    chksum = chk.getValue();
  } catch (Exception e) {
    e.printStackTrace();
  }

  // After creating your apk, calculate the crc32 checksum
  // and store it as a string value in the KEY / unlock App.
  String keyStrVal = getKeyString(tt_crc32);
  
  // Key is not installed.
  if ( keyStrVal.equals("") ) {
    // Key not installed. Validation failure.
  }
  
  Long chksumCmp = Long.parseLong(keyStrVal);
  
  if ( chksum.equals(chksumCmp) ) {
    // Success. Checksum stored in key matches the
    // checksum we just created. We can assume APK
    // is not modified. Kinda.
  }
  else {
    // Validation failure! Apk has been modified.
  }
}

public static TestResult checkMD5ChkSum() {
  // Do pretty much the exact same thing here,
  // except instead of a CRC32 checksum, we'll be
  // using an MD5 digest. You could also use SHA1.
  // Any cracker worth his salt will immediately recognize
  // CRC32 and MD5 keywords and know them to be checksum
  // attempts. Using Adler32 or SHA1 may put them off.
  String apkPath = Main.MyContext.getPackageCodePath();
  MessageDigest msgDigest = null;
  byte[] digest = null;
  try {
    msgDigest = MessageDigest.getInstance("MD5");
  } catch (NoSuchAlgorithmException e1) {
    e1.printStackTrace();
  }
  
  byte[] bytes = new byte[8192];
  int byteCount;
  FileInputStream fis = null;
  
  try {
    fis = new FileInputStream(new File(apkPath));

    while ((byteCount = fis.read(bytes)) > 0)
      msgDigest.update(bytes, 0, byteCount);
    
    digest = msgDigest.digest();
  } catch (Exception e) {
    e.printStackTrace();
  }

  String keyStrVal = getKeyString(tt_md5);
  // Key is not installed.
  if ( keyStrVal.equals("") ) {
    // Key not installed. Validation failure.
  }

  // Using Base64 encoding is just a lazy way to store byte arrays.
  // You -could- also embed the values in the code of the Apk
  // Read more here:
  // http://stackoverflow.com/questions/2721386/android-how-to-share-code-between-projects-signed-with-the-same-certificate
  if ( Arrays.equals(Base64.decode(keyStrVal, Base64.DEFAULT), digest) )
    // Validated
  else
    // Apk has been modified
}


private static String getKeyString(int resId) {
  // You will need this to retrieve the stored checksums from the KEY App.
  String result = "";
  
  try {
    Context c = Main.MyContext.createPackageContext("your.package.name.key", Context.CONTEXT_IGNORE_SECURITY);
    result = c.getString(resId);
  } catch (Exception e) {
    Console.log("Error while getting key string:\n" + e);
    e.printStackTrace();
    result = "";
  }
  
  return result;
}

and here's what the above java looks like in smali, so you have some idea what to look for. cracking this will require you to write an app that simulates how the app calculates the checksum. then you'll have to come up with a clever way to get the value into the smali. if it's a long number, this is fairly easy, but if it's a byte array, you may need to use base64 encoding or some other method to make a byte array safe for literal strings. the keywords to look for, of course, are md5, sha1, crc32 and adler32. they may not appear at all if the developer is using reflection to make the method calls.

.method public static checkCRC32ChkSum()V
    .locals 11

    .prologue
    .line 934
    sget-object v9, Lcom/lohan/testtarget/Main;->MyContext:Landroid/content/Context;

    invoke-virtual {v9}, Landroid/content/Context;->getPackageCodePath()Ljava/lang/String;

    move-result-object v0

    .line 935
    .local v0, apkPath:Ljava/lang/String;
    const/4 v3, 0x0

    .line 939
    .local v3, chksum:Ljava/lang/Long;
    :try_start_0
    new-instance v7, Ljava/io/FileInputStream;

    new-instance v9, Ljava/io/File;

    invoke-direct {v9, v0}, Ljava/io/File;->(Ljava/lang/String;)V

    invoke-direct {v7, v9}, Ljava/io/FileInputStream;->(Ljava/io/File;)V

    .line 940
    .local v7, fis:Ljava/io/FileInputStream;
    new-instance v2, Ljava/util/zip/CRC32;

    invoke-direct {v2}, Ljava/util/zip/CRC32;->()V

    .line 942
    .local v2, chk:Ljava/util/zip/CRC32;
    new-instance v5, Ljava/util/zip/CheckedInputStream;

    invoke-direct {v5, v7, v2}, Ljava/util/zip/CheckedInputStream;->(Ljava/io/InputStream;Ljava/util/zip/Checksum;)V

    .line 943
    .local v5, cis:Ljava/util/zip/CheckedInputStream;
    const/16 v9, 0x50

    new-array v1, v9, [B

    .line 944
    .local v1, buff:[B
    :cond_0
    invoke-virtual {v5, v1}, Ljava/util/zip/CheckedInputStream;->read([B)I

    move-result v9

    if-gez v9, :cond_0

    .line 946
    invoke-virtual {v2}, Ljava/util/zip/CRC32;->getValue()J

    move-result-wide v9

    invoke-static {v9, v10}, Ljava/lang/Long;->valueOf(J)Ljava/lang/Long;
    :try_end_0
    .catch Ljava/lang/Exception; {:try_start_0 .. :try_end_0} :catch_0

    move-result-object v3

    .line 953
    .end local v1           #buff:[B
    .end local v2           #chk:Ljava/util/zip/CRC32;
    .end local v5           #cis:Ljava/util/zip/CheckedInputStream;
    .end local v7           #fis:Ljava/io/FileInputStream;
    :goto_0
    const v9, 0x7f040002

    invoke-static {v9}, Lcom/lohan/testtarget/PerformTestsTask;->getKeyString(I)Ljava/lang/String;

    move-result-object v8

    .line 956
    .local v8, keyStrVal:Ljava/lang/String;
    const-string v9, ""

    invoke-virtual {v8, v9}, Ljava/lang/String;->equals(Ljava/lang/Object;)Z

    .line 960
    invoke-static {v8}, Ljava/lang/Long;->parseLong(Ljava/lang/String;)J

    move-result-wide v9

    invoke-static {v9, v10}, Ljava/lang/Long;->valueOf(J)Ljava/lang/Long;

    move-result-object v4

    .line 962
    .local v4, chksumCmp:Ljava/lang/Long;
    invoke-virtual {v3, v4}, Ljava/lang/Long;->equals(Ljava/lang/Object;)Z

    .line 970
    return-void

    .line 947
    .end local v4           #chksumCmp:Ljava/lang/Long;
    .end local v8           #keyStrVal:Ljava/lang/String;
    :catch_0
    move-exception v9

    move-object v6, v9

    .line 948
    .local v6, e:Ljava/lang/Exception;
    invoke-virtual {v6}, Ljava/lang/Exception;->printStackTrace()V

    goto :goto_0
.end method

.method public static checkMD5ChkSum()V
    .locals 12

    .prologue
    const/4 v11, 0x0

    .line 981
    sget-object v10, Lcom/lohan/testtarget/Main;->MyContext:Landroid/content/Context;

    invoke-virtual {v10}, Landroid/content/Context;->getPackageCodePath()Ljava/lang/String;

    move-result-object v0

    .line 982
    .local v0, apkPath:Ljava/lang/String;
    const/4 v9, 0x0

    .line 983
    .local v9, msgDigest:Ljava/security/MessageDigest;
    const/4 v3, 0x0

    check-cast v3, [B

    .line 985
    .local v3, digest:[B
    :try_start_0
    const-string v10, "MD5"

    invoke-static {v10}, Ljava/security/MessageDigest;->getInstance(Ljava/lang/String;)Ljava/security/MessageDigest;
    :try_end_0
    .catch Ljava/security/NoSuchAlgorithmException; {:try_start_0 .. :try_end_0} :catch_0

    move-result-object v9

    .line 990
    :goto_0
    const/16 v10, 0x2000

    new-array v2, v10, [B

    .line 992
    .local v2, bytes:[B
    const/4 v6, 0x0

    .line 995
    .local v6, fis:Ljava/io/FileInputStream;
    :try_start_1
    new-instance v7, Ljava/io/FileInputStream;

    new-instance v10, Ljava/io/File;

    invoke-direct {v10, v0}, Ljava/io/File;->(Ljava/lang/String;)V

    invoke-direct {v7, v10}, Ljava/io/FileInputStream;->(Ljava/io/File;)V
    :try_end_1
    .catch Ljava/lang/Exception; {:try_start_1 .. :try_end_1} :catch_2

    .line 997
    .end local v6           #fis:Ljava/io/FileInputStream;
    .local v7, fis:Ljava/io/FileInputStream;
    :goto_1
    :try_start_2
    invoke-virtual {v7, v2}, Ljava/io/FileInputStream;->read([B)I

    move-result v1

    .local v1, byteCount:I
    if-gtz v1, :cond_0

    .line 1000
    invoke-virtual {v9}, Ljava/security/MessageDigest;->digest()[B
    :try_end_2
    .catch Ljava/lang/Exception; {:try_start_2 .. :try_end_2} :catch_1

    move-result-object v3

    move-object v6, v7

    .line 1005
    .end local v1           #byteCount:I
    .end local v7           #fis:Ljava/io/FileInputStream;
    .restart local v6       #fis:Ljava/io/FileInputStream;
    :goto_2
    const v10, 0x7f040004

    invoke-static {v10}, Lcom/lohan/testtarget/PerformTestsTask;->getKeyString(I)Ljava/lang/String;

    move-result-object v8

    .line 1007
    .local v8, keyStrVal:Ljava/lang/String;
    const-string v10, ""

    invoke-virtual {v8, v10}, Ljava/lang/String;->equals(Ljava/lang/Object;)Z

    .line 1015
    invoke-static {v8, v11}, Landroid/util/Base64;->decode(Ljava/lang/String;I)[B

    move-result-object v10

    invoke-static {v10, v3}, Ljava/util/Arrays;->equals([B[B)Z

    .line 1020
    return-void

    .line 986
    .end local v2           #bytes:[B
    .end local v6           #fis:Ljava/io/FileInputStream;
    .end local v8           #keyStrVal:Ljava/lang/String;
    :catch_0
    move-exception v10

    move-object v5, v10

    .line 987
    .local v5, e1:Ljava/security/NoSuchAlgorithmException;
    invoke-virtual {v5}, Ljava/security/NoSuchAlgorithmException;->printStackTrace()V

    goto :goto_0

    .line 998
    .end local v5           #e1:Ljava/security/NoSuchAlgorithmException;
    .restart local v1       #byteCount:I
    .restart local v2       #bytes:[B
    .restart local v7       #fis:Ljava/io/FileInputStream;
    :cond_0
    const/4 v10, 0x0

    :try_start_3
    invoke-virtual {v9, v2, v10, v1}, Ljava/security/MessageDigest;->update([BII)V
    :try_end_3
    .catch Ljava/lang/Exception; {:try_start_3 .. :try_end_3} :catch_1

    goto :goto_1

    .line 1001
    .end local v1           #byteCount:I
    :catch_1
    move-exception v10

    move-object v4, v10

    move-object v6, v7

    .line 1002
    .end local v7           #fis:Ljava/io/FileInputStream;
    .local v4, e:Ljava/lang/Exception;
    .restart local v6       #fis:Ljava/io/FileInputStream;
    :goto_3
    invoke-virtual {v4}, Ljava/lang/Exception;->printStackTrace()V

    goto :goto_2

    .line 1001
    .end local v4           #e:Ljava/lang/Exception;
    :catch_2
    move-exception v10

    move-object v4, v10

    goto :goto_3
.end method

.method private static asdfgetKeyString(I)Ljava/lang/String;
    .locals 6
    .parameter "resId"

    .prologue
    .line 1025
    const-string v2, ""

    .line 1028
    .local v2, result:Ljava/lang/String;
    :try_start_0
    sget-object v3, Lcom/lohan/testtarget/Main;->MyContext:Landroid/content/Context;

    const-string v4, "your.package.name.key"

    const/4 v5, 0x2

    invoke-virtual {v3, v4, v5}, Landroid/content/Context;->createPackageContext(Ljava/lang/String;I)Landroid/content/Context;

    move-result-object v0

    .line 1029
    .local v0, c:Landroid/content/Context;
    invoke-virtual {v0, p0}, Landroid/content/Context;->getString(I)Ljava/lang/String;
    :try_end_0
    .catch Ljava/lang/Exception; {:try_start_0 .. :try_end_0} :catch_0

    move-result-object v2

    .line 1036
    .end local v0           #c:Landroid/content/Context;
    :goto_0
    return-object v2

    .line 1030
    :catch_0
    move-exception v3

    move-object v1, v3

    .line 1031
    .local v1, e:Ljava/lang/Exception;
    new-instance v3, Ljava/lang/StringBuilder;

    const-string v4, "Error while getting key string:\n"

    invoke-direct {v3, v4}, Ljava/lang/StringBuilder;->(Ljava/lang/String;)V

    invoke-virtual {v3, v1}, Ljava/lang/StringBuilder;->append(Ljava/lang/Object;)Ljava/lang/StringBuilder;

    move-result-object v3

    invoke-virtual {v3}, Ljava/lang/StringBuilder;->toString()Ljava/lang/String;

    move-result-object v3

    invoke-static {v3}, Lcom/lohan/testtarget/Console;->log(Ljava/lang/String;)V

    .line 1032
    invoke-virtual {v1}, Ljava/lang/Exception;->printStackTrace()V

    .line 1033
    const-string v2, ""

    goto :goto_0
.end method

cracking verizon's v cast apps drm

verizon has a new app store. it has an amazon-store like drm that's fairly simple to crack.

here's how it works. in the launching activity a thread is started that calls checkLicense(). this was in com/cp/app/MainActivity$2.smali:

.method public run()V
    .locals 2

    .prologue
    .line 100
    invoke-static {}, Landroid/os/Looper;->prepare()V

    .line 102
    :try_start_0
    iget-object v0, p0, Lcom/cp/app/MainActivity$2;->this$0:Lcom/cp/app/MainActivity;

    iget-object v0, v0, Lcom/cp/app/MainActivity;->licenseAuthenticator:Lcom/verizon/vcast/apps/LicenseAuthenticator;

    sget-object v1, Lcom/cp/app/MainActivity;->verizonAppKeyword:Ljava/lang/String;

    # call checkLicense and store result in v0
    invoke-virtual {v0, v1}, Lcom/verizon/vcast/apps/LicenseAuthenticator;->checkLicense(Ljava/lang/String;)I
    move-result v0

    .line 103
    iget-object v1, p0, Lcom/cp/app/MainActivity$2;->this$0:Lcom/cp/app/MainActivity;

    # send result of checkLicense (v0) to isDRMDone()
    invoke-virtual {v1, v0}, Lcom/cp/app/MainActivity;->isDRMDone(I)Z
    move-result v0

    # isDRMDone() handles error messages and returns true when all is good
    if-eqz v0, :cond_0

    # ... rest of code

if you look at isDRMDone() you'll see that it's basically a big switch. input of 0 or 1 counts as valid. everything else is some kind of error. so we just need to make sure checkLicense returns 1 and doesn't call anything else that may have side effects (timeouts, checking to see if verizon app store is installed, etc..).

checkLicense() is defined in com/verizon/vcast/apps/LicenseAuthenticator.smali. after modification it looks like:

.method public declared-synchronized checkLicense(Ljava/lang/String;)I
    .locals 10
    .parameter "keyword"

    .prologue
    
    # just set v0 to true and return
    # the rest of the code never runs
    const/4 v0, 0x1
    return v0

    const/16 v9, 0x64

    const-string v7, "checkLicense() finished.  Trying to shutDownLicenseService()"

    const-string v7, "LicenseAuthenticator"

    .line 256
    monitor-enter p0

    :try_start_0
    const-string v7, "LicenseAuthenticator"

    const-string v8, "begin checkLicense()"

    # ... rest of code

if you're a developer, depending on how they implement the insertion of their drm, it may still be possible to use classical protection / anti-tampering techniques. i'd like to know. but really though, don't waste your time on protection. i'm not blasting verizon or amazon or google for weak security. real effort should be spent improving the program, not slowing down (because you can't stop) crackers. if you want money, use ads.

anti-tampering with crc check

one way an app will try to detect if it has been tampered with is to look at classes.dex inside the apk. just so you know, java code is compiled to java .class files, which is then transformed by dx into classes.dex. this one file contains all the compiled code of an app. once the code is finished and the app is ready to be published, properties of the file such as the size or crc (cyclic redundancy check) can be determined and then stored inside the resources of the app.

when the app runs, it can compare the stored values with the actual values of the classes.dex file. if they do not match, then the code was likely tampered with.

note that we're using zipentry here, but we could also use jarentry and jarfile. you can't simply look for getCrc() and feel safe either, because the method could be called with reflection.

here's what a crc check may look like in java:

private void crcTest() throws IOException {
 boolean modified = false;

 // required dex crc value stored as a text string.
 // it could be any invisible layout element
 long dexCrc = Long.parseLong(Main.MyContext.getString(R.string.dex_crc));

 ZipFile zf = new ZipFile(Main.MyContext.getPackageCodePath());
 ZipEntry ze = zf.getEntry("classes.dex");

 if ( ze.getCrc() != dexCrc ) {
  // dex has been modified
  modified = true;
 }
 else {
  // dex not tampered with
  modified = false;
 }
}

and here's the above code translated into smali:

.method private crcTest()V
    .locals 7
    .annotation system Ldalvik/annotation/Throws;
        value = {
            Ljava/io/IOException;
        }
    .end annotation

    .prologue
    .line 599
    const/4 v2, 0x0

    .line 602
    # modified will be set to true if classes.dex crc is not what it should be
    .local v2, modified:Z
    sget-object v5, Lcom/lohan/testtarget/Main;->MyContext:Landroid/content/Context;

    # get the crc value from string resources
    const v6, 0x7f040002
    invoke-virtual {v5, v6}, Landroid/content/Context;->getString(I)Ljava/lang/String;
    move-result-object v5

    # convert it to a long since ZipEntry.getCrc gives us long
    invoke-static {v5}, Ljava/lang/Long;->parseLong(Ljava/lang/String;)J
    move-result-wide v0

    .line 604
    .local v0, dexCrc:J
    new-instance v4, Ljava/util/zip/ZipFile;

    sget-object v5, Lcom/lohan/testtarget/Main;->MyContext:Landroid/content/Context;

    # get the path to the apk on the system
    invoke-virtual {v5}, Landroid/content/Context;->getPackageCodePath()Ljava/lang/String;
    move-result-object v5

    invoke-direct {v4, v5}, Ljava/util/zip/ZipFile;->(Ljava/lang/String;)V

    .line 605
    .local v4, zf:Ljava/util/zip/ZipFile;
    # get classes.dex entry from our apk
    const-string v5, "classes.dex"
    invoke-virtual {v4, v5}, Ljava/util/zip/ZipFile;->getEntry(Ljava/lang/String;)Ljava/util/zip/ZipEntry;
    move-result-object v3

    .line 607
    .local v3, ze:Ljava/util/zip/ZipEntry;
    # you could crack here by providing v5 with the correct
    # long value. this may be easier if later logic is convoluted
    # or if the result is stored in a class variable and acted
    # on later. you can write your own java program to get the

    # correct value. 

    invoke-virtual {v3}, Ljava/util/zip/ZipEntry;->getCrc()J
    move-result-wide v5

    # compare v5 (actual crc) with v0 (stored crc)
    cmp-long v5, v5, v0

    # if v5 is 0, meaning cmp-long reports values are NOT the same
    # goto :cond_0. this is where this could be cracked.
    # could simply remove this line, in this case.
    if-eqz v5, :cond_0

    .line 609
    # otherwise store true in v2.
    # normally there will be code to act on the value of v2.
    const/4 v2, 0x1

    .line 615
    :goto_0
    return-void

    .line 613
    :cond_0
    # store false in v2.
    const/4 v2, 0x0

    goto :goto_0
.end method

protection by checking for debuggers

one way to figure out what an app is doing is to use a debugger so you can step through line by line. apktool makes it possible to debug apps to which you do not have the source, and you also have to setup a few other things covered in lesson 1 of the way of the android crack tutorials.

some apps try to protect against this and there are two techniques of doing so. the first is to check the android manifest to see if the app is set to debuggable. the java code would look something like this:

boolean isDebuggable = (0 != (getApplcationInfo().flags &= ApplicationInfo.FLAG_DEBUGGABLE));
if ( isDebuggable )
  invalidLicense(); // you get the idea 

in smali, specifically from the testtarget app distributed with antilvl, it looks like:

# get app info object
invoke-virtual {p0}, Lcom/lohan/testtarget/Main;->getApplicationInfo()Landroid/content/pm/ApplicationInfo;
move-result-object v1

# get flags mask
iget v2, v1, Landroid/content/pm/ApplicationInfo;->flags:I

# 0x2 is ApplicationInfo.FLAG_DEBUGGABLE
and-int/lit8 v2, v2, 0x2

iput v2, v1, Landroid/content/pm/ApplicationInfo;->flags:I

# if v2 is 0x0 (the debuggable flag is not set), goto :cond_0
if-eqz v2, :cond_0

the second method is to check if a debugger is currently connected. the java looks like:

boolean debugConn = Debug.isDebuggerConnected();

smali syntax resource

jesusfreke, the guy who wrote smali/baksmali, has some nice documentation on the smali syntax on the wiki for his project: http://code.google.com/p/smali/w/list i learned some stuff! thanks jesusfreke.

antilvl 1.1.5

thanks to Notion and SuRViVe pointing out some instances of the lvl not being properly identified. i removed some requirements to match some key files that weren't likely necessary and were not being found recently. two new anti-cracking methods have been added and testtarget was updated appropriately.

grab it here:
http://androidcracking.blogspot.com/p/antilvl_01.html