Implicit declaration of function 'sqlite3_key'?

I am working on SQLite File Encryption. I have added sqlCipher & crypto frameworks successfully in my project.

Now when I try to compile my application on this line

int rc = sqlite3_key(database, [key UTF8String], strlen([key UTF8String]));

it says Implicit declaration of function 'sqlite3_key'

So above line "implicit declaration" sounds to me like function is defined but not declared. But where I have to declared ?

While searching over Internet, under this article, it says like SQLite Encryption Extension(SEE) is not available publically. I have to purchase it of cost around $2000.

SEE -> http://www.hwaci.com/sw/sqlite/see.html

So this is the only reason I am getting Implicit declaration & False response while sqlite encryption process ?