this is the method that will generate for you the key hash of your machine to add it to your facebook app page on developer

key hash for facebook

// will generate key hash for android for facebook 
public String printKeyHash() {
        PackageInfo packageInfo;
        String key = null;
        try {
            //getting application package name, as defined in manifest
            String packageName = this.getApplicationContext().getPackageName();

            //Retriving package info
            packageInfo = this.getPackageManager().getPackageInfo(packageName,
                    PackageManager.GET_SIGNATURES);

            Log.e("Package Name=", this.getApplicationContext().getPackageName());

            for (android.content.pm.Signature signature : packageInfo.signatures) {
                MessageDigest md = MessageDigest.getInstance("SHA");
                md.update(signature.toByteArray());
                key = new String(Base64.encode(md.digest(), 0));

                // String key = new String(Base64.encodeBytes(md.digest()));
                Log.e("Key Hash =", key);
            }
        } catch (PackageManager.NameNotFoundException e1) {
            Log.e("Name not found", e1.toString());
        } catch (NoSuchAlgorithmException e) {
            Log.e("No such an algorithm", e.toString());
        } catch (Exception e) {
            Log.e("Exception", e.toString());
        }

        return key;
    }