diff --git a/week4.py b/week4.py
new file mode 100644
index 0000000..5d16dd1
--- /dev/null
+++ b/week4.py
@@ -0,0 +1,119 @@
+# Concept: Create 8 PKs where each represent a bloodtype. Let 7 of them be created by OGen and 1 of them by KeyGen.
+# The one represents our bloodtype. Bob will then encrypt 8 values using these PKs, where each value repredents
+# A truth value, thus either true or false, s.t. each cipher is an entry in the bloodtype comptability matrix.
+
+import secrets
+import numpy as np
+from crypto.week1 import BloodType, convert_from_string_to_enum, blood_cell_compatibility_lookup
+
+convert_bloodtype_to_index = {
+    BloodType.O_NEGATIVE: 0,
+    BloodType.O_POSITIVE: 1,
+    BloodType.A_NEGATIVE: 2,
+    BloodType.A_POSITIVE: 3,
+    BloodType.B_NEGATIVE: 4,
+    BloodType.B_POSITIVE: 5,
+    BloodType.AB_NEGATIVE: 6,
+    BloodType.AB_POSITIVE: 7,
+}
+
+
+class Group:
+    def __init__(self, q):
+        self.order = q
+
+    def gen_group_stuff(self):
+        my_group = []
+        for i in range(1, self.order):
+            if np.gcd(i, self.order) == 1:
+                my_group.append(i)
+        for group_ele in my_group:
+            if group_ele**self.order == 1 % self.order:
+                gen = group_ele
+        return gen, self.order, my_group
+
+class ElGamal:
+    def __init__(self, G, g, q):
+        self.group = G
+        self.gen_ = g
+        self.order = q
+        self.pk = None
+        self.sk = None
+
+    def gen(self, sk):
+        h = self.gen_**sk
+        self.sk = sk
+        self.pk = (self.gen_, h)
+        return self.pk
+
+    def enc(self, m, pk):
+        # sample random r \in Zq
+        r = secrets.SystemRandom().randint(1, self.order-1)
+        g, h = pk
+        c = (g ** r, m * h**r)
+        return c
+
+    def dec(self, c):
+        c1, c2 = c
+        m = c2 * c1**(-self.sk) # % self.order
+        return m
+
+    def ogen(self, r):
+        # Here, q = 2p+1, thus we actually need to use the p here, instead of
+        # self.order, but as we do not know p yet, .e we
+        # TODO: Use p instead of self.order, s.t. self.order = 2p+1
+        s = secrets.SystemRandom().randint(1, self.order)
+        h = s**2 % self.order
+        return self.gen_, h
+
+
+class Alice:
+    def __init__(self, bloodtype, elgamal):
+        self.elgamal = elgamal
+        self.gen_ = 9
+        self.order = 453
+        self.b = convert_bloodtype_to_index[convert_from_string_to_enum[bloodtype]]
+        self.sk = secrets.SystemRandom().randint(1, self.order)
+
+        self.pk = self.elgamal.gen(self.sk)
+        self.fake_pks = [self.elgamal.ogen(secrets.SystemRandom().randint(0, self.order))
+                         for _ in range(7)]
+
+    def send_pks(self):
+        all_pks = self.fake_pks
+        all_pks.insert(self.b, self.pk)
+        return all_pks
+
+    def retrieve(self, ciphers):
+        mb = self.elgamal.dec(ciphers[self.b])
+        return mb
+
+
+class Bob:
+    def __init__(self, bloodtype, elgamal):
+        self.bloodtype = convert_from_string_to_enum[bloodtype]
+        self.truth_vals = []
+        self.elgamal = elgamal
+        self.pks = None
+        for donor in BloodType:
+            truth_val = blood_cell_compatibility_lookup(self.bloodtype, donor)
+            self.truth_vals.append(truth_val)
+
+    def receive_pks(self, pks):
+        self.pks = pks
+
+    def transfer_messages(self):
+        ciphers = []
+        for idx, truth_val in enumerate(self.truth_vals):
+            pk = self.pks[idx]
+            c = self.elgamal.enc(truth_val, pk)
+            ciphers.append(c)
+        return ciphers
+
+
+if __name__ == "__main__":
+    group = Group(11)
+    gen, order, my_group = group.gen_group_stuff()
+
+    print(gen, order, my_group)
+