encryption of an already existing database for SQLCipher

Question

I use an already existing database in my App (see also 1). I encrypted the database with a Java Application. In my App I try to read the encrypted_database with the following code, but I get a SQLiteException: file is encrypted or is not a database:

    SQLiteDatabase.loadLibs(mContext);
    SQLiteDatabase dataBase = SQLiteDatabase.openDatabase(mPath, mPassword, null, SQLiteDatabase.OPEN_READONLY);
    String query = "Select distinct _id from TABLE";
    Cursor cursor = dataBase.rawQuery(query, null);
    return cursor;

I already encrypted my database with SQLCipher and I also can read the data, so everything works fine.

The problem with SQLCipher and an already existing database is that I have to copy the complete unencrypted_database to an encrypted_database. This takes a long time when I do this on my phone.

My idea was: Write an Application in java that encrypts the database and take this encrypted_database in your app. This has the result that I just have to open the already existing encrypted_database in my app and no copying is required.

Now I wrote an Java Application (based on 2,3) but there are still some questions related to SQLCipher and its design (4):

how can I divide my database in database pages? In 4 a database page is just defined by its size (1024 bytes). But what I have to write into my encrypted_database file to say "database page starts" or "database page ends"

is the salt and the random initialization vector (iv) part of the 1024 bytes?

public static void main(String[] args) throws Exception{

    outFile_enc = new FileOutputStream(mFileNameEncrypted);
    outFile_dec = new FileOutputStream(mFileNameDecrypted);

    int keyLength = 256;
    // salt
    salt = new byte[16];
    Random rnd = new Random();
    rnd.nextBytes(salt);
    int iterations = 4000;

    SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
    KeySpec keySpec = new PBEKeySpec(mPassWord.toCharArray(), salt, iterations, keyLength);
    SecretKey passwordKey = keyFactory.generateSecret(keySpec);
    key = new SecretKeySpec(passwordKey.getEncoded(), "AES");

    // creates a cipher and init it for encryption
    Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
    cipher.init(Cipher.ENCRYPT_MODE, key);

    AlgorithmParameters params = cipher.getParameters();
    iv = params.getParameterSpec(IvParameterSpec.class).getIV();

    encryptData(cipher);            
}

public static void encryptData(Cipher cipher) throws Exception{
    // File to encrypt
    inFile = new FileInputStream(mFileName);

    // unique random salt in the first 16 bytes of the file
    outFile_enc.write(salt);

    // Read file and encrypt its bytes
    byte[] input  = new byte[64];
    int bytesRead;
    while((bytesRead = inFile.read(input)) != -1){
    byte[] output = cipher.update(input, 0, bytesRead);
    if(output != null)
        outFile_enc.write(output);
    }

    byte[] output = cipher.doFinal();
    if(output != null)
        outFile_enc.write(output);
    // random initialization vector is stored at the end of a page
    outFile_enc.write(iv);

    inFile.close();
    outFile_enc.flush();
    outFile_enc.close();    
}

I appreciate every help/idea/comment :)

score 2 · Accepted Answer · answered Dec 21 '12 at 13:35

2

THe approach of trying to recreate a SQLCipher file from scratch is not advised. The format is more complicated than what you are doing, and it will be non-trivial reproduce a valid SQLCipher file. Instead, you should just use the SQLCipher command line program to encrypt your database for distribution.

answered Dec 21 '12 at 13:35

Stephen Lombardo

1,503
8
7

Thank you for the answer. I saw the SQLCipher API, but I didn't understand how to solve my problem. Your answer helped me to get an idea :). I'll try it next time. – owe Dec 23 '12 at 12:51

encryption of an already existing database for SQLCipher

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