diff --git a/.github/workflows/build-backend.yml b/.github/workflows/build-backend.yml
new file mode 100644
index 0000000..bd688af
--- /dev/null
+++ b/.github/workflows/build-backend.yml
@@ -0,0 +1,33 @@
+name: Build Frontend
+on:
+  push:
+    paths:
+      - 'backend/**'
+      - '.github/workflows/**'
+    branches:
+      - main
+
+  pull_request:
+    paths:
+      - 'backend/**'
+      - '.github/workflows/**'
+    types:
+      - opened
+      - synchronize
+      - reopened
+
+jobs:
+  sonarcloud:
+    name: SonarCloud Backend
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 0  # Shallow clones should be disabled for a better relevancy of analysis
+      - name: SonarCloud Scan
+        uses: SonarSource/sonarcloud-github-action@master
+        with:
+          projectBaseDir: backend  
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}  # Needed to get PR information, if any
+          SONAR_TOKEN: ${{ secrets.SONAR_TOKEN_BACKEND }}
diff --git a/.github/workflows/build-frontend.yml b/.github/workflows/build-frontend.yml
new file mode 100644
index 0000000..f385c48
--- /dev/null
+++ b/.github/workflows/build-frontend.yml
@@ -0,0 +1,33 @@
+name: Build Frontend
+on:
+  push:
+    paths:
+      - 'frontend/**'
+      - '.github/workflows/**'
+    branches:
+      - main
+
+  pull_request:
+    paths:
+      - 'frontend/**'
+      - '.github/workflows/**'
+    types:
+      - opened
+      - synchronize
+      - reopened
+
+jobs:
+  sonarcloud:
+    name: SonarCloud Frontend
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 0  # Shallow clones should be disabled for a better relevancy of analysis
+      - name: SonarCloud Scan
+        uses: SonarSource/sonarcloud-github-action@master
+        with:
+          projectBaseDir: frontend  
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}  # Needed to get PR information, if any
+          SONAR_TOKEN: ${{ secrets.SONAR_TOKEN_FRONTEND }}
diff --git a/backend/app/dependencies/qrvalidation.py b/backend/app/dependencies/qrvalidation.py
new file mode 100644
index 0000000..2ce85fd
--- /dev/null
+++ b/backend/app/dependencies/qrvalidation.py
@@ -0,0 +1,62 @@
+import os
+from hashlib import sha256
+import hmac
+import time
+import base64
+
+
+validity = 3600 # seconds (int)
+
+k = os.urandom(32)
+
+
+def sign(data: str) -> str:
+    hmac_sha256 = hmac.new(k, digestmod=sha256)
+    hmac_sha256.update(data.encode())
+    t = int(time.time())
+    expiration = t + validity
+    expiration = expiration.to_bytes(4, byteorder='big')
+    hmac_sha256.update(expiration)
+    hash = hmac_sha256.digest()
+    # xor the first 16 bytes with the last 16 bytes
+    hash = bytes([a ^ b for a, b in zip(hash[:16], hash[16:])])
+    # base85 encode the hash
+    signature = base64.b85encode(expiration + hash)
+    return signature.decode()
+
+
+def verify(data: str) -> bool:
+    if len(data) < 25:
+        return False
+    
+    signature = base64.b85decode(data[-25:].encode())
+    expiration = int.from_bytes(signature[:4], byteorder='big')
+    if expiration < time.time():
+        return False
+    
+    msg = data[:-25]
+    hmac_sha256 = hmac.new(k, digestmod=sha256)
+    hmac_sha256.update(msg.encode())
+    hmac_sha256.update(signature[:4])
+    hash = hmac_sha256.digest()
+    hash = bytes([a ^ b for a, b in zip(hash[:16], hash[16:])])
+    return hash == signature[4:]
+
+
+def encode(data: str) -> str:
+    return data + sign(data)
+
+
+def decode(data: str) -> str:
+    if verify(data):
+        return data[:-25]
+    return None
+
+
+if __name__ == "__main__":
+    signed_msg = sign("Hello World")
+    print(signed_msg)
+    print(verify(signed_msg))
+    signed_msg = signed_msg[:-1] + "A" # tamper with the message
+    print(verify(signed_msg))
+    
\ No newline at end of file
diff --git a/backend/app/main.py b/backend/app/main.py
index 5adbba8..1866a7d 100644
--- a/backend/app/main.py
+++ b/backend/app/main.py
@@ -2,8 +2,7 @@
 from fastapi.middleware.cors import CORSMiddleware
 
 from app.dependencies.database import Base, engine
-
-from app.routes import auth, desafios
+from app.routes import auth, qrcode, desafios
 from app import models
 
 Base.metadata.create_all(bind=engine)
@@ -12,6 +11,7 @@
 
 
 app.include_router(auth.router)
+app.include_router(qrcode.router)
 app.include_router(desafios.router)
 
 origins = [
diff --git a/backend/app/models/atividade.py b/backend/app/models/atividade.py
index d2d4286..9c51559 100644
--- a/backend/app/models/atividade.py
+++ b/backend/app/models/atividade.py
@@ -10,12 +10,8 @@ class Atividade(Base):
     id: Mapped[int] = mapped_column("id", Integer, primary_key=True)
     nome: Mapped[str] = mapped_column(String(255), nullable=False)
     pontos: Mapped[int] = mapped_column(Integer, default=0)
-    #empresa_id: Mapped[int] = mapped_column(
-    #    ForeignKey(f"empresas.id", ondelete="CASCADE"),
-    #    nullable=False
-    #)
-
-    #empresa: Mapped["Empresas"] = relationship("Empresas", back_populates="atividades")
+    
+    empresa: Mapped[List["Empresas"]] = relationship("Empresas", back_populates="atividades")
     eventos: Mapped[List["Eventos"]] = relationship("Eventos", back_populates="atividade")
     desafios: Mapped[List["Desafios"]] = relationship("Desafios", back_populates="atividade")
     participacoes: Mapped[List["Participacao"]] = relationship("Participacao", back_populates="atividade")
\ No newline at end of file
diff --git a/backend/app/models/desafios.py b/backend/app/models/desafios.py
index 9e6d7c6..0661964 100644
--- a/backend/app/models/desafios.py
+++ b/backend/app/models/desafios.py
@@ -11,10 +11,10 @@ class Desafios(Base):
         nullable=False
     )
     descricao: Mapped[str] = mapped_column(Text, nullable=False)
-    #empresa_id: Mapped[int] = mapped_column(
-    #    ForeignKey(f"empresas.id", ondelete="CASCADE"),
-    #    nullable=False
-    #)
+    empresa_id: Mapped[int] = mapped_column(
+        ForeignKey(f"empresas.id", ondelete="CASCADE"),
+        nullable=False
+    )
 
     atividade: Mapped["Atividade"] = relationship("Atividade", back_populates="desafios")
-    #empresa: Mapped["Empresas"] = relationship("Empresas", back_populates="desafios")
\ No newline at end of file
+    empresa: Mapped["Empresas"] = relationship("Empresas", back_populates="desafios")
\ No newline at end of file
diff --git a/backend/app/models/empresas.py b/backend/app/models/empresas.py
index 385f0c9..682a821 100644
--- a/backend/app/models/empresas.py
+++ b/backend/app/models/empresas.py
@@ -14,9 +14,14 @@ class Empresas(Base):
         nullable=False
     )
     sponsor_type: Mapped[str] = mapped_column(String(50), nullable=True)
+
+    atividade_id: Mapped[int] = mapped_column(
+        ForeignKey(f"atividade.id", ondelete="CASCADE"),
+        nullable=False
+    )
     spotlight_time: Mapped[TIMESTAMP] = mapped_column(TIMESTAMP, nullable=True)
 
     user: Mapped["Users"] = relationship("Users", back_populates="empresas")
-    #atividades: Mapped[List["Atividade"]] = relationship("Atividade", back_populates="empresa")
+    atividades: Mapped["Atividade"] = relationship("Atividade", back_populates="empresa")
     eventos: Mapped[List["Eventos"]] = relationship("Eventos", back_populates="empresa")
-    #desafios: Mapped[List["Desafios"]] = relationship("Desafios", back_populates="empresa")
\ No newline at end of file
+    desafios: Mapped[List["Desafios"]] = relationship("Desafios", back_populates="empresa")
\ No newline at end of file
diff --git a/backend/app/routes/desafios.py b/backend/app/routes/desafios.py
index d79fa7b..499e4eb 100644
--- a/backend/app/routes/desafios.py
+++ b/backend/app/routes/desafios.py
@@ -43,11 +43,11 @@ def create_desafio(
 
         # return joined object
         return Desafio(
-            id=db_desafio.id,
-            nome=db_atividade.nome,
-            pontos=db_atividade.pontos,
-            descricao=db_desafio.descricao,
-        )
+                id=db_desafio.id,
+                nome=db_atividade.nome,
+                pontos=db_atividade.pontos,
+                descricao=db_desafio.descricao,
+            )
     except Exception as e:
         db.rollback()
         return HTTPException(status_code=400, detail=str(e))
@@ -57,7 +57,12 @@ def create_desafio(
 def read_desafios(skip: int = 0, limit: int = 10, db: Session = Depends(get_db)):
     # Join 'Atividade' and 'Desafios' tables
     db_desafios = (
-        db.query(Desafios.id, Atividade.nome, Atividade.pontos, Desafios.descricao)
+        db.query(
+            Desafios.id,
+            Atividade.nome,
+            Atividade.pontos,
+            Desafios.descricao,
+            )
         .join(Atividade, Desafios.atividade_id == Atividade.id)
         .offset(skip)
         .limit(limit)
@@ -71,7 +76,12 @@ def read_desafios(skip: int = 0, limit: int = 10, db: Session = Depends(get_db))
 def read_desafio(desafio_id: int, db: Session = Depends(get_db)):
     # Join 'Atividade' and 'Desafios' tables
     db_desafio = (
-        db.query(Desafios.id, Atividade.nome, Atividade.pontos, Desafios.descricao)
+        db.query(
+            Desafios.id,
+            Atividade.nome,
+            Atividade.pontos,
+            Desafios.descricao,
+            )
         .join(Atividade, Desafios.atividade_id == Atividade.id)
         .filter(Desafios.id == desafio_id)
         .first()
@@ -92,7 +102,12 @@ def update_desafio(
 
     # Join 'Atividade' and 'Desafios' tables
     db_desafio = (
-        db.query(Desafios.id, Atividade.nome, Atividade.pontos, Desafios.descricao)
+        db.query(
+            Desafios.id,
+            Atividade.nome,
+            Atividade.pontos,
+            Desafios.descricao,
+            )
         .join(Atividade, Desafios.atividade_id == Atividade.id)
         .filter(Desafios.id == desafio_id)
         .first()
@@ -105,9 +120,9 @@ def update_desafio(
         {"nome": desafio.nome, "pontos": desafio.pontos}
     )
     # update 'Desafios' object
-    db.query(Desafios).filter(Desafios.id == db_desafio.id).update(
-        {"descricao": desafio.descricao}
-    )
+    db.query(Desafios).filter(Desafios.id == db_desafio.id).update({
+        "descricao": desafio.descricao,
+    })
     db.commit()
 
     # return updated object
@@ -129,7 +144,12 @@ def delete_desafio(
 
     # Join 'Atividade' and 'Desafios' tables
     db_desafio = (
-        db.query(Desafios.id, Atividade.nome, Atividade.pontos, Desafios.descricao)
+        db.query(
+            Desafios.id,
+            Atividade.nome,
+            Atividade.pontos,
+            Desafios.descricao,
+            )
         .join(Atividade, Desafios.atividade_id == Atividade.id)
         .filter(Desafios.id == desafio_id)
         .first()
diff --git a/backend/app/routes/qrcode.py b/backend/app/routes/qrcode.py
new file mode 100644
index 0000000..af18f13
--- /dev/null
+++ b/backend/app/routes/qrcode.py
@@ -0,0 +1,53 @@
+from fastapi import APIRouter, HTTPException
+from fastapi.responses import StreamingResponse
+
+import io
+import qrcode
+
+from app.dependencies import qrvalidation
+from app.schemas.qrcode import QRCodeRequest
+
+router = APIRouter(
+    prefix="/qrcode",
+    tags=["qrcode"],
+    responses={404: {"description": "Not found"}}
+)
+
+@router.post("/encode")
+async def qrcode_encode(data: QRCodeRequest):
+    if not data:
+        raise HTTPException(status_code=400, detail="No data provided")
+    
+    # TODO: Use auth to validate user
+    
+    msg = data.msg
+
+    qr = qrcode.QRCode(
+        version=1,
+        error_correction=qrcode.constants.ERROR_CORRECT_L,
+        box_size=10,
+        border=4,
+    )
+    qr.add_data(qrvalidation.encode(msg))
+    qr.make(fit=True)
+
+    img = qr.make_image(fill='black', back_color='white')
+    img_io = io.BytesIO()
+    img.save(img_io, 'PNG')
+    img_io.seek(0)
+
+    return StreamingResponse(img_io, media_type="image/png")
+    
+@router.post("/decode")
+async def qrcode_decode(data: QRCodeRequest):
+    if not data:
+        raise HTTPException(status_code=400, detail="No data provided")
+    
+    msg = data.msg
+
+    userId = qrvalidation.decode(msg)
+
+    if userId is None:
+        raise HTTPException(status_code=400, detail="Invalid QR code")
+
+    return {"msg": userId}
diff --git a/backend/app/schemas/atividades.py b/backend/app/schemas/atividades.py
index a1640ff..c08b4d5 100644
--- a/backend/app/schemas/atividades.py
+++ b/backend/app/schemas/atividades.py
@@ -4,15 +4,3 @@
 class AtividadeBase(BaseModel):
     nome: str
     pontos: Optional[int] = 0
-
-class AtividadeCreate(AtividadeBase):
-    pass
-
-class AtividadeUpdate(AtividadeBase):
-    pass
-
-class Atividade(AtividadeBase):
-    id: int
-
-    class Config:
-        from_attributes = True
diff --git a/backend/app/schemas/desafios.py b/backend/app/schemas/desafios.py
index aa1d040..410db29 100644
--- a/backend/app/schemas/desafios.py
+++ b/backend/app/schemas/desafios.py
@@ -4,7 +4,7 @@
 
 class DesafioBase(AtividadeBase):
     descricao: str
-    #empresa_id: int
+    empresa_id: int
 
 class DesafioCreate(DesafioBase):
     pass
diff --git a/backend/app/schemas/qrcode.py b/backend/app/schemas/qrcode.py
new file mode 100644
index 0000000..fb8928c
--- /dev/null
+++ b/backend/app/schemas/qrcode.py
@@ -0,0 +1,6 @@
+from pydantic import BaseModel
+
+
+
+class QRCodeRequest(BaseModel):
+    msg: str
diff --git a/backend/examples/README.md b/backend/examples/README.md
new file mode 100644
index 0000000..3577bc5
--- /dev/null
+++ b/backend/examples/README.md
@@ -0,0 +1,5 @@
+# Examples
+
+ These examples demonstrate the integration between different components of the system.
+
+**They only serve as support for project development and do not constitute an integral part of the system.**
\ No newline at end of file
diff --git a/backend/examples/qrcode/generate.html b/backend/examples/qrcode/generate.html
new file mode 100644
index 0000000..ba03bb4
--- /dev/null
+++ b/backend/examples/qrcode/generate.html
@@ -0,0 +1,39 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <title>QR Code Generator</title>
+    <script>
+        async function generateQRCode() {
+            event.preventDefault();
+            const input = document.getElementById("inputText").value;
+            const response = await fetch("http://127.0.0.1:8000/qrcode/encode", {
+                method: "POST",
+                headers: {
+                    "Content-Type": "application/json"
+                },
+                body: JSON.stringify({ msg: input })
+            });
+
+            if (response.ok) {
+                const blob = await response.blob();
+                const url = URL.createObjectURL(blob);
+                document.getElementById("qrcodeImage").src = url;
+            } else {
+                alert("Failed to generate QR Code");
+            }
+        }
+    </script>
+</head>
+<body>
+    <h1>QR Code Generator</h1>
+    <!-- button to /scan -->
+    <a href="/scan">QR Code Scanner</a>
+    <br><br>
+    <form onsubmit="generateQRCode(event)">
+        <input type="text" id="inputText" placeholder="Enter text" required>
+        <button type="submit">Generate QR Code</button>
+    </form>
+    <br><br>
+    <img id="qrcodeImage" alt="QR Code will be displayed here">
+</body>
+</html>
diff --git a/backend/examples/qrcode/index.html b/backend/examples/qrcode/index.html
new file mode 100644
index 0000000..cdcbdb6
--- /dev/null
+++ b/backend/examples/qrcode/index.html
@@ -0,0 +1,15 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <title>QR Code</title>
+</head>
+<body>
+    <h1>QR Code</h1>
+    <!-- button to /generate -->
+    <a href="generate.html">QR Code Generator</a>
+    <br><br>
+    <!-- button to /scan -->
+    <a href="scan.html">QR Code Scanner</a>
+    <br><br>
+</body>
+</html>
diff --git a/backend/examples/qrcode/scan.html b/backend/examples/qrcode/scan.html
new file mode 100644
index 0000000..10da465
--- /dev/null
+++ b/backend/examples/qrcode/scan.html
@@ -0,0 +1,47 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <title>QR Code Scanner</title>
+    <script src="https://cdnjs.cloudflare.com/ajax/libs/html5-qrcode/2.1.4/html5-qrcode.min.js"></script>
+    <script>
+        async function onScanSuccess(text, result) {
+            const response = await fetch("http://127.0.0.1:8000/qrcode/decode", {
+                method: "POST",
+                headers: {
+                    "Content-Type": "application/json"
+                },
+                body: JSON.stringify({ msg: text })
+            })
+
+            if (response.ok) {
+                const data = await response.json();
+                document.getElementById("result").innerText = "Deti4Devs QRCode Status: VALID\n\nContent: " + data.msg;
+            } else {
+                document.getElementById("result").innerText = "Deti4Devs QRCode Status: INVALID\n\nContent: " + text;
+            }
+            
+        }
+
+        function onScanError(errorMessage) {
+            console.error(`Error scanning: ${errorMessage}`);
+        }
+
+        document.addEventListener('DOMContentLoaded', function() {
+            const html5QrcodeScanner = new Html5QrcodeScanner(
+                "reader", { fps: 10, qrbox: 600 }
+            );
+            html5QrcodeScanner.render(onScanSuccess, onScanError);
+        });
+    </script>
+</head>
+<body>
+    <h1>QR Code Scanner</h1>
+    <div id="reader" style="width:90%;margin:auto"></div>
+    <div>
+        <h2 style="font-size: 35pt;"
+        >Scanned QR Code Result:</h2>
+        <p id="result" style="font-size: 25pt;"
+        ></p>
+    </div>
+</body>
+</html>
\ No newline at end of file
diff --git a/backend/requirements.txt b/backend/requirements.txt
index fd32a2e..ec2e247 100644
--- a/backend/requirements.txt
+++ b/backend/requirements.txt
@@ -38,3 +38,4 @@ uvicorn==0.30.5
 uvloop==0.19.0
 watchfiles==0.22.0
 websockets==12.0
+qrcode==7.4.2
diff --git a/backend/sonar-project.properties b/backend/sonar-project.properties
new file mode 100644
index 0000000..e800ec4
--- /dev/null
+++ b/backend/sonar-project.properties
@@ -0,0 +1,12 @@
+sonar.projectKey=d4d-backend
+sonar.organization=aettua
+
+# This is the name and version displayed in the SonarCloud UI.
+#sonar.projectName=d4d-backend
+#sonar.projectVersion=1.0
+
+# Path is relative to the sonar-project.properties file. Replace "\" by "/" on Windows.
+sonar.sources=.
+
+# Encoding of the source code. Default is default system encoding
+#sonar.sourceEncoding=UTF-8
diff --git a/frontend/sonar-project.properties b/frontend/sonar-project.properties
new file mode 100644
index 0000000..f22298f
--- /dev/null
+++ b/frontend/sonar-project.properties
@@ -0,0 +1,12 @@
+sonar.projectKey=d4d-frontend
+sonar.organization=aettua
+
+# This is the name and version displayed in the SonarCloud UI.
+#sonar.projectName=d4d-frontend
+#sonar.projectVersion=1.0
+
+# Path is relative to the sonar-project.properties file. Replace "\" by "/" on Windows.
+sonar.sources=.
+
+# Encoding of the source code. Default is default system encoding
+#sonar.sourceEncoding=UTF-8