package cfb1

import (
    "crypto/cipher"
    "errors"
)

  // NewCFB1 returns a stream cipher that implements CFB-1 mode.  The key argument should be the AES key, either 16, 24, or 32 bytes to select AES-128, AES-192, or AES-256.
func NewCFB1(key []byte) (cipher.Stream, error) {

    // check key length is valid for AES encryption algorithm 
    if len(key) != 16 && len(key) != 24 && len(key) != 32 {  // not valid key length for AES encryption algorithm 

    return nil, errors.New("invalid key size")   // return an error if invalid key length is provided

    } else {   // valid key length for AES encryption algorithm

        // create a new instance of cfb1 struct and return it as type of cipher.Stream interface