diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
new file mode 100644
index 0000000..a6f09b0
--- /dev/null
+++ b/.github/workflows/build.yml
@@ -0,0 +1,50 @@
+name: Build
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        php-versions: ['8.1', '8.2', '8.3']
+
+    steps:
+      - name: Checkout source
+        uses: actions/checkout@v2
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php-versions }}
+          ini-values: memory_limit=2048M
+    
+      - name: Get composer cache directory
+        id: composer-cache
+        run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+
+      - name: Cache dependencies
+        uses: actions/cache@v2
+        with:  
+          path: ${{ steps.composer-cache.outputs.dir }}
+          key: ${{ matrix.php-versions }}-composer-${{ hashFiles('**/composer.json') }}
+          restore-keys: ${{ matrix.php-versions }}-composer-
+
+      - name: Install dependencies
+        run: composer install --prefer-dist
+        
+      - name: Check code standards
+        run: vendor/bin/phpcs --standard=PSR1,PSR2 -n src
+
+      - name: Run useragent string tests
+        run: php bin/runner.php --show check
+
+      - name: Run unit tests
+        run: vendor/bin/phpunit --no-coverage tests/unit
\ No newline at end of file
diff --git a/source/AlnumVigenereCipher.php b/source/AlnumVigenereCipher.php
index bf14c3a..301377a 100644
--- a/source/AlnumVigenereCipher.php
+++ b/source/AlnumVigenereCipher.php
@@ -1,6 +1,9 @@
 <?php
 namespace amculin\cryptography\classic;
 
+use amculin\cryptography\classic\enums\ProcessType;
+use amculin\cryptography\classic\exceptions\InvalidAlnumException;
+
 /**
  * This file is the main class for alpha-numric mode vigenere cipher algortithm
  *
@@ -17,4 +20,36 @@ class AlnumVigenereCipher extends VigenereCipherBlueprint
      * @var string
      */
     public $tabulaRecta = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
+
+    public function isValid(): bool
+    {
+        try {
+            $pattern = '/^[a-zA-Z0-9]*$/';
+            $isValid = preg_match($pattern, $this->key);
+
+            if (! $isValid) {
+                throw new InvalidAlnumException('Key');
+            }
+
+            if ($this->process == ProcessType::ENCRYPT->value) {
+                $isValid = preg_match($pattern, $this->plainText) && $isValid;
+
+                if (! $isValid) {
+                    throw new InvalidAlnumException('Plain text');
+                }
+            } else {
+                $isValid = preg_match($pattern, $this->cipherText) && $isValid;
+
+                if (! $isValid) {
+                    throw new InvalidAlnumException('Cipher text');
+                }
+            }
+        } catch(InvalidAlnumException $e) {
+            echo $e->errorMessage();
+
+            return false;
+        }
+
+        return true;
+    }
 }
diff --git a/source/BasicVigenereCipher.php b/source/BasicVigenereCipher.php
index 80f151b..f4b615e 100644
--- a/source/BasicVigenereCipher.php
+++ b/source/BasicVigenereCipher.php
@@ -1,6 +1,9 @@
 <?php
 namespace amculin\cryptography\classic;
 
+use amculin\cryptography\classic\enums\ProcessType;
+use amculin\cryptography\classic\exceptions\InvalidBasicException;
+
 /**
  * This file is the main class for basic vigenere cipher algortithm
  *
@@ -14,4 +17,36 @@ class BasicVigenereCipher extends VigenereCipherBlueprint
      * @inheritdoc
      */
     public $tabulaRecta = 'abcdefghijklmnopqrstuvwxyz';
+
+    public function isValid(): bool
+    {
+        try {
+            $pattern = '/^[a-z]*$/';
+            $isValid = preg_match($pattern, $this->key);
+
+            if (! $isValid) {
+                throw new InvalidBasicException('Key');
+            }
+
+            if ($this->process == ProcessType::ENCRYPT->value) {
+                $isValid = preg_match($pattern, $this->plainText) && $isValid;
+
+                if (! $isValid) {
+                    throw new InvalidBasicException('Plain text');
+                }
+            } else {
+                $isValid = preg_match($pattern, $this->cipherText) && $isValid;
+
+                if (! $isValid) {
+                    throw new InvalidBasicException('Cipher text');
+                }
+            }
+        } catch(InvalidBasicException $e) {
+            echo $e->errorMessage();
+
+            return false;
+        }
+
+        return true;
+    }
 }
diff --git a/source/VigenereCipher.php b/source/VigenereCipher.php
index 7695caa..e0aa1a2 100644
--- a/source/VigenereCipher.php
+++ b/source/VigenereCipher.php
@@ -17,7 +17,7 @@ public static function getClassName(string $mode): string
         }
     }
 
-    public static function encrypt(string $data, string $key, string $mode = 'basic'): string
+    public static function encrypt(string $data, string $key, string $mode = 'basic'): string|null
     {
         $className = self::getClassName($mode);
 
@@ -28,7 +28,7 @@ public static function encrypt(string $data, string $key, string $mode = 'basic'
         return $encrypt->getCipherText();
     }
 
-    public static function decrypt(string $data, string $key, string $mode = 'basic'): string
+    public static function decrypt(string $data, string $key, string $mode = 'basic'): string|null
     {
         $className = self::getClassName($mode);
 
diff --git a/source/VigenereCipherBlueprint.php b/source/VigenereCipherBlueprint.php
index c1d58cb..bd434d6 100644
--- a/source/VigenereCipherBlueprint.php
+++ b/source/VigenereCipherBlueprint.php
@@ -49,17 +49,25 @@ public function __construct(string $process = 'encrypt', string $data = null, st
             if (! is_null($data) && ! is_null($key)) {
                 $this->setPlainText($data);
                 $this->setKey($key);
-                $this->encrypt();
+
+                if ($this->isValid()) {
+                    $this->encrypt();
+                }
             }
         } else {
             if (! is_null($data) && ! is_null($key)) {
                 $this->setCipherText($data);
                 $this->setKey($key);
-                $this->decrypt();
+
+                if ($this->isValid()) {
+                    $this->decrypt();
+                }
             }
         }
     }
 
+    abstract public function isValid(): bool;
+
     /**
      * Method to get current process
      *
@@ -86,7 +94,7 @@ public function setProcess(string $process): void
      *
      * @return string
      */
-    public function getPlainText(): string
+    public function getPlainText(): string|null
     {
         return $this->plainText;
     }
@@ -130,7 +138,7 @@ public function setKey(string $key): void
      *
      * @return string
      */
-    public function getCipherText(): string
+    public function getCipherText(): string|null
     {
         return $this->cipherText;
     }
diff --git a/source/exceptions/InvalidAlnumException.php b/source/exceptions/InvalidAlnumException.php
new file mode 100644
index 0000000..a550793
--- /dev/null
+++ b/source/exceptions/InvalidAlnumException.php
@@ -0,0 +1,12 @@
+<?php
+namespace amculin\cryptography\classic\exceptions;
+
+class InvalidAlnumException extends \Exception
+{
+    public function errorMessage() {
+        $message = 'Error on line ' . $this->getLine() . ' in ' . $this->getFile() . ': '. PHP_EOL;
+        $message .= $this->getMessage() . ' is invalid, must be combination of a-z, A-Z, and 0-9!' . PHP_EOL;
+
+        return $message;
+    }
+}
diff --git a/source/exceptions/InvalidBasicException.php b/source/exceptions/InvalidBasicException.php
new file mode 100644
index 0000000..70e293a
--- /dev/null
+++ b/source/exceptions/InvalidBasicException.php
@@ -0,0 +1,12 @@
+<?php
+namespace amculin\cryptography\classic\exceptions;
+
+class InvalidBasicException extends \Exception
+{
+    public function errorMessage() {
+        $message = 'Error on line ' . $this->getLine() . ' in ' . $this->getFile() . ': '. PHP_EOL;
+        $message .= $this->getMessage() . ' is invalid, must be combination of a-z!' . PHP_EOL;
+
+        return $message;
+    }
+}
diff --git a/tests/VIgenereCipherTest.php b/tests/VIgenereCipherTest.php
index 9669c13..fb9befb 100644
--- a/tests/VIgenereCipherTest.php
+++ b/tests/VIgenereCipherTest.php
@@ -6,9 +6,12 @@
 
 final class VigenereCipherTest extends TestCase
 {
-    public function testCanEncryptWithBasicMode():void
+    const BASIC_ALLOWED_CHARS = '/[a-z]/';
+    const ALNUM_ALLOWED_CHARS = '/[a-zA-Z0-9]/';
+
+    public function testCanEncryptInBasicMode():void
     {
-        $allowedChars = '/[a-z]/';
+        $allowedChars = $this::BASIC_ALLOWED_CHARS;
         $data = 'encryptionprocess';
         $key = 'thekey';
 
@@ -25,9 +28,19 @@ public function testCanEncryptWithBasicMode():void
         $this->assertMatchesRegularExpression($allowedChars, $encrypted);
     }
 
-    public function testCanDecryptWithBasicMode():void
+    public function testCanNotEncryptInBasicModeWithInvalidKey():void
+    {
+        $data = 'encryptionprocess';
+        $key = 'thekey-';
+
+        $encrypted = VigenereCipher::encrypt($data, $key, VigenereMode::BASIC->value);
+
+        $this->assertNull($encrypted);
+    }
+
+    public function testCanDecryptInBasicMode():void
     {
-        $allowedChars = '/[a-z]/';
+        $allowedChars = $this::BASIC_ALLOWED_CHARS;
         $data = 'xugbcnmpsxtphjicw';
         $key = 'thekey';
 
@@ -44,9 +57,19 @@ public function testCanDecryptWithBasicMode():void
         $this->assertMatchesRegularExpression($allowedChars, $decrypted);
     }
 
-    public function testCanEncryptWithAlphaNumericMode():void
+    public function testCanNotDecryptInBasicModeWithInvalidKey():void
+    {
+        $data = 'xugbcnmpsxtphjicw';
+        $key = 'thekey-';
+
+        $encrypted = VigenereCipher::decrypt($data, $key, VigenereMode::BASIC->value);
+
+        $this->assertNull($encrypted);
+    }
+
+    public function testCanEncryptInAlphaNumericMode():void
     {
-        $allowedChars = '/[a-zA-Z0-9]/';
+        $allowedChars = $this::ALNUM_ALLOWED_CHARS;
         $data = 'Encrypti0nProC3s5';
         $key = 'th3kEy';
 
@@ -63,9 +86,19 @@ public function testCanEncryptWithAlphaNumericMode():void
         $this->assertMatchesRegularExpression($allowedChars, $encrypted);
     }
 
+    public function testCanNotEncryptInAlphaNumericModeWithInvalidKey():void
+    {
+        $data = 'Encrypti0nProC3s5';
+        $key = 'th3kEy-';
+
+        $encrypted = VigenereCipher::encrypt($data, $key, VigenereMode::ALPHA_NUMERIC->value);
+
+        $this->assertNull($encrypted);
+    }
+
     public function testCanDecryptWithAlphaNumericMode():void
     {
-        $allowedChars = '/[a-zA-Z0-9]/';
+        $allowedChars = $this::ALNUM_ALLOWED_CHARS;
         $data = 'Xu5B2NMpTxjPHJWCz';
         $key = 'th3kEy';
 
@@ -82,6 +115,16 @@ public function testCanDecryptWithAlphaNumericMode():void
         $this->assertMatchesRegularExpression($allowedChars, $decrypted);
     }
 
+    public function testCanNotDecryptInAlphaNumericModeWithInvalidKey():void
+    {
+        $data = 'Xu5B2NMpTxjPHJWCz';
+        $key = 'th3kEy-';
+
+        $encrypted = VigenereCipher::decrypt($data, $key, VigenereMode::ALPHA_NUMERIC->value);
+
+        $this->assertNull($encrypted);
+    }
+
     public function testCanGetBasicVigenereClass(): void
     {
         $path = 'amculin\cryptography\classic\\';