reset SQLCipher cipher_page_size cause open database error - sqlcipher

Question

Based on the intro from offical site of SQLCipher, set the cipher_page_size should right after "PRAGMA KEY = 'testkey';". So I create my own DatabaseHelper as following:
public class DatabaseHelper extends SQLiteOpenHelper {
private final static String NEWDBNAME="my.db" ;
public DatabaseHelper(Context context){
super(context, NEWDBNAME, null, 0 ,new SQLiteDatabaseHook(){
#Override
public void postKey(SQLiteDatabase arg0) {
arg0.rawExecSQL("PRAGMA cipher_page_size = 4096");
}
#Override
public void preKey(SQLiteDatabase arg0) {
}});
}
public void onCreate(SQLiteDatabase db) { }
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { }
public SQLiteDatabase getWritableDatabase()
{
return getWritableDatabase("encodestr");
}
}
The issue is my android application will got an error like : the file is not a db or is encripted...
When I comments: //arg0.rawExecSQL("PRAGMA cipher_page_size = 4096"); , it will run well.
Anybody know this issue?
Thanks.

Answer 1

If the database already exists, unless it was initially created with a cipher_page_size set to 4096, you would need to export the encrypted database with the new setting. Doing so will allow all of the pages to be rewritten to the new block size. An example:
$ ./sqlcipher foo.db
sqlcipher> PRAGMA key = 'foo';
sqlcipher> create table t1(a,b);
sqlcipher> insert into table t1(a,b) values('one for the money', 'two for the show');
sqlcipher> .q
Now foo.db has a default cipher_page_size of 1024, let's export the database with a new cipher_page_size of 4096:
$ ./sqlcipher foo.db
sqlcipher> PRAGMA key = 'foo';
sqlcipher> ATTACH DATABASE 'bar.db' as bar KEY 'foo';
sqlcipher> PRAGMA bar.cipher_page_size = 4096;
sqlcipher> SELECT sqlcipher_export('bar');
sqlcipher> DETACH database bar;
sqlcipher> .q
Now we will need to specify the cipher_page_size when querying the database:
$ ./sqlcipher bar.db
sqlcipher> PRAGMA key = 'foo';
sqlcipher> PRAGMA cipher_page_size = 4096;
sqlcipher> SELECT count(*) from sqlite_master;
count(*)
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1