diff --git a/CRC.java b/CRC.java
new file mode 100644
index 0000000..687e7e9
--- /dev/null
+++ b/CRC.java
@@ -0,0 +1,15 @@
+public class CRC {
+    public static void main(String[] args) {
+        try {
+            if (args[1].equals("-e")){
+                Encoding tmp = new Encoding(args[0]);
+                System.out.println(args[0] + tmp.getFcsChars());
+            } else if (args[1].equals("-d")){
+                Decoding d = new Decoding(args[0]);
+                System.out.println(d.getCheck());
+            }
+        } catch (ArrayIndexOutOfBoundsException e){
+            System.out.println("Za mało argumentów");
+        }
+    }
+}
\ No newline at end of file
diff --git a/Decoding.java b/Decoding.java
new file mode 100644
index 0000000..73f12ca
--- /dev/null
+++ b/Decoding.java
@@ -0,0 +1,60 @@
+import java.util.ArrayList;
+import java.util.Collections;
+
+public class Decoding {
+    private Boolean check;
+
+    public Decoding(String arg){
+        Polynomials poly = new Polynomials(2);
+        ArrayList<Byte> message = new ArrayList<>();
+        ArrayList<Integer> g = new ArrayList<>();
+        ArrayList<Integer> l = new ArrayList<>();
+        ArrayList<Integer> tmp = new ArrayList<>();
+        ArrayList<Integer> tmp2 = new ArrayList<>();
+
+        for (int i = 0; i < arg.length(); ++i){
+            message.add((byte)arg.charAt(i));
+        }
+        for (int i = 0; i < 16; ++i){
+            if (i == 12 || i == 5 || i==0){
+                g.add(1);
+            } else{
+                g.add(0);
+            }
+            l.add(1);
+        }
+        g.add(1);
+
+        for (int i = 0; i < 16 ; ++i){
+            tmp.add(0);
+        }
+        for (byte b : message){
+            String s2 = String.format("%8s", Integer.toBinaryString(b & 0xFF)).replace(' ', '0');
+            for (int i = 0; i < 8; ++i){
+                tmp2.add(Character.getNumericValue(s2.charAt(i)));
+            }
+        }
+        Collections.reverse(tmp2);
+        tmp.addAll(tmp2);
+        tmp2.clear();
+        for (int i = 0; i < arg.length() * 8; ++i) tmp2.add(0);
+        for (int i = 0; i < 16; ++i) tmp2.add(1);
+
+        tmp = poly.divModN(poly.add(tmp, tmp2),g);
+
+        if (tmp.size() == 0) {
+            check = true;
+        } else
+            check = false;
+
+//        String m = arg.substring(0, arg.length()-2);
+//        String fcs = arg.substring(arg.length()-2);
+//        Encoding e = new Encoding(m);
+//        if (e.getFcsChars().equals(fcs)) check = true;
+//        else check = false;
+    }
+
+    public Boolean getCheck() {
+        return check;
+    }
+}
\ No newline at end of file
diff --git a/Encoding.java b/Encoding.java
new file mode 100644
index 0000000..4974926
--- /dev/null
+++ b/Encoding.java
@@ -0,0 +1,65 @@
+import java.util.ArrayList;
+import java.util.Collections;
+
+public class Encoding {
+    private ArrayList<Integer> fcs;
+
+    public Encoding(String args) {
+        ArrayList<Byte> message = new ArrayList<>();
+        ArrayList<Integer> g = new ArrayList<>();
+        fcs = new ArrayList<>();
+        Polynomials poly = new Polynomials(2);
+
+        for (int i = 0; i < args.length(); ++i){
+            message.add((byte)args.charAt(i));
+        }
+        for (int i = 0; i < 16; ++i){
+            if (i == 12 || i == 5 || i==0){
+                g.add(1);
+            } else{
+                g.add(0);
+            }
+        }
+        g.add(1);
+
+        ArrayList<Integer> tmp = new ArrayList<>();
+        ArrayList<Integer> tmp2 = new ArrayList<>();
+        for (int i = 0; i < 16 ; ++i){
+            tmp.add(0);
+        }
+        for (byte b : message){
+            String s2 = String.format("%8s", Integer.toBinaryString(b & 0xFF)).replace(' ', '0');
+            for (int i = 0; i < 8; ++i){
+                tmp2.add(Character.getNumericValue(s2.charAt(i)));
+            }
+        }
+        Collections.reverse(tmp2);
+        tmp.addAll(tmp2);
+        tmp2.clear();
+
+        for (int i = 0; i < args.length() * 8; ++i) tmp2.add(0);
+        for (int i = 0; i < 16; ++i) tmp2.add(1);
+
+        fcs = poly.divModN(poly.add(tmp, tmp2), g);
+        while(fcs.size() < 16) fcs.add(0);
+        Collections.reverse(fcs);
+    }
+
+    public ArrayList<Integer> getFcs() {
+        return fcs;
+    }
+
+    public String getFcsChars(){
+        int a = 0;
+        int b = 0;
+        for (int i = 0; i < 8; ++i){
+            if (fcs.get(i) == 1){
+                a += Math.pow(2, 7-i);
+            }
+            if (fcs.get(i + 8) == 1){
+                b += Math.pow(2, 7-i);
+            }
+        }
+        return Character.toString((char)a) + Character.toString((char)b);
+    }
+}
\ No newline at end of file
diff --git a/Polynomials.java b/Polynomials.java
new file mode 100644
index 0000000..fb0ab55
--- /dev/null
+++ b/Polynomials.java
@@ -0,0 +1,121 @@
+import java.util.ArrayList;
+
+public class Polynomials {
+    int n;
+
+    public Polynomials(int n) {
+        this.n = n;
+    }
+
+    private ArrayList<Integer> normalize(ArrayList<Integer> w){
+        for (int i = w.size()-1; i >= 0; --i){
+            if (w.get(i).equals(0)) {
+                w.remove(i);
+            }else {
+                return w;
+            }
+        }
+        return w;
+    }
+
+    public ArrayList<Integer> multiply(ArrayList<Integer> f, ArrayList<Integer> g){
+        ArrayList<Integer> result = new ArrayList<>();
+        int tmp;
+
+        for (int i = 0; i < f.size(); ++i){
+            for (int j = 0; j < g.size(); ++j){
+                tmp = f.get(i) * g.get(j);
+                if (i + j < result.size()){
+                    tmp += result.get(i+j);
+                    result.set(i + j, tmp % n);
+                } else {
+                    while ((i + j) >= (result.size())){
+                        result.add(0);
+                    }
+                    result.set(i + j, tmp % n);
+                }
+            }
+        }
+        return (result);
+    }
+
+    private int getZero(int a, int b) throws ArithmeticException{
+        for (int i = 0; i <= n; ++i){
+            if ((a + (-(b * i))) == 0) return i;
+        }
+        throw new ArithmeticException("not reversible");
+    }
+
+    public ArrayList<Integer> multiplyByConst(ArrayList<Integer> f, Integer a){
+        ArrayList<Integer> result = new ArrayList<>();
+        for (Integer i : f){
+            result.add((i * a) % n);
+        }
+        return result;
+    }
+
+    public ArrayList<Integer> subtract(ArrayList<Integer> f, ArrayList<Integer> g){
+        ArrayList<Integer> result = new ArrayList<>();
+        for (int i = 0; i < f.size(); ++i){
+            if (i < g.size()){
+                result.add(Math.floorMod(f.get(i) - g.get(i), n));
+            } else{
+                result.add(f.get(i));
+            }
+        }
+        return result;
+    }
+
+    public ArrayList<Integer> add(ArrayList<Integer> f, ArrayList<Integer> g){
+        ArrayList<Integer> result = new ArrayList<>();
+        if (f.size() >= g.size()) {
+            for (int i = 0; i < f.size(); ++i) {
+                if (i < g.size()) {
+                    result.add(Math.floorMod(f.get(i) + g.get(i), n));
+                } else {
+                    result.add(f.get(i));
+                }
+            }
+        } else{
+            for (int i = 0; i < g.size(); ++i) {
+                if (i < f.size()) {
+                    result.add(Math.floorMod(f.get(i) + g.get(i), n));
+                } else {
+                    result.add(g.get(i));
+                }
+            }
+        }
+        return result;
+    }
+
+    public ArrayList<Integer> divModN(ArrayList<Integer> f, ArrayList<Integer> g) throws ArithmeticException{
+        ArrayList<Integer> quotient = new ArrayList<>();
+        ArrayList<Integer> remainder = new ArrayList<>(f);
+        ArrayList<Integer> tmpList;
+        int a = f.size() - 1;
+        int b = g.size() - 1;
+
+        for (int i = 0; i < a - b + 1; ++i){
+            quotient.add(0);
+        }
+
+        int q = quotient.size()-1;
+        int tmp;
+        while (a >= b) {
+            tmp = getZero(remainder.get(a), g.get(b));
+            quotient.set(q--, tmp);
+            tmpList = multiplyByConst(g, tmp);
+            while(tmpList.size() <= a) tmpList.add(0,0);
+            remainder = subtract(remainder, tmpList);
+            --a;
+        }
+        return normalize(remainder);
+    }
+
+    public ArrayList<Integer> gcc (ArrayList<Integer> f, ArrayList<Integer> g){
+        if (g.size() == 0) return f;
+        if (f.size() > g.size()){
+            return gcc(g, divModN(f, g));
+        } else return gcc(g, divModN(g, f));
+    }
+}
\ No newline at end of file