SQLCipher: verify key against open database - c

Question

Is it possible to check if a given key is a correct decryption for already open and unlocked database?
#define SQLITE_HAS_CODEC
#include <sqlcipher/sqlite3.h>
#include <assert.h>
sqlite3 *open_db(void)
{
sqlite3 *dbh;
sqlite3_open_v2("test.db", &dbh, SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE, NULL);
sqlite3_key(dbh, "xxxx", 4);
return dbh;
}
int key_is_valid(sqlite3 *dbh, const char *key)
{
/* ??? */
return 1;
}
int main(int argc, char *argv[])
{
sqlite3 *dbh = open_db();
assert(key_is_valid(dbh, "test"));
assert(!key_is_valid(dbh, "foobar"));
return 0;
}
I know I could store decryption key passed to sqlite3_key for later verification, but I'd like to avoid it.
The reason I need to do this is that I want to allow users to change password, and before that I want them to provide old one.

Answer 1

You can verify the password provided is valid following the keying of the database by attempting to read from the sqlite_master table:
SELECT count(*) FROM sqlite_master;
The library requires the correct password is provided before changing the password. Once you have properly keyed the database, you can change the password using the following API:
int sqlite3_rekey(sqlite3 *db, const void *pKey, int nKey);