Create a small library for AES128 / AES192 / AES256 Encryption and decryption of a file created by QT in C++

For data encryption we need a small lib code which can be attached to any QT Project and can be used to can encrypt and decrypt a complete file with an (seed) password. The code has to be proprietary and no open source obligations . Following functions are required :- Function 1 1) Encrypt a text file (size > 10 kb < 100kb) using a key ("string input given by user ") 2) Decrypt the text file using the same key as described above. Function 2 1) Decrypt a text file (size > 10 kb < 100kb) using the key provided. 2) Check if the decrypted file is indeed correct.(decryption key is same as encryption key) Text file here can contain numbers, alphabets and special characters.