diff --git a/src/lib/security/captcha.test.ts b/src/lib/security/captcha.test.ts
new file mode 100644
index 0000000..db47560
--- /dev/null
+++ b/src/lib/security/captcha.test.ts
@@ -0,0 +1,46 @@
+import { generateCaptcha, validateCaptcha, CaptchaResult } from './captcha';
+
+describe('Enhanced Captcha System', () => {
+  test('should generate captcha with medium complexity', () => {
+    const result = generateCaptcha('medium');
+    expect(result).toBeDefined();
+    expect(result.question).toBeDefined();
+    expect(result.answer).toBeDefined();
+    expect(result.hash).toBeDefined();
+    expect(result.timestamp).toBeDefined();
+    expect(typeof result.question).toBe('string');
+    expect(typeof result.answer).toBe('number');
+  });
+
+  test('should generate different captcha each time', () => {
+    const result1 = generateCaptcha('medium');
+    const result2 = generateCaptcha('medium');
+    expect(result1.hash).not.toBe(result2.hash);
+  });
+
+  test('should validate correct captcha answer', () => {
+    const captcha = generateCaptcha('medium');
+    const isValid = validateCaptcha(captcha.hash, captcha.answer, captcha.timestamp);
+    expect(isValid).toBe(true);
+  });
+
+  test('should reject incorrect captcha answer', () => {
+    const captcha = generateCaptcha('medium');
+    const isValid = validateCaptcha(captcha.hash, captcha.answer + 1, captcha.timestamp);
+    expect(isValid).toBe(false);
+  });
+
+  test('should reject expired captcha', () => {
+    const captcha = generateCaptcha('medium');
+    const expiredTimestamp = Date.now() - (6 * 60 * 1000); // 6 minutes ago
+    const isValid = validateCaptcha(captcha.hash, captcha.answer, expiredTimestamp);
+    expect(isValid).toBe(false);
+  });
+
+  test('should generate complex captcha', () => {
+    const result = generateCaptcha('complex');
+    expect(result).toBeDefined();
+    const numbers = result.question.match(/\d+/g);
+    expect(numbers?.length).toBeGreaterThan(2);
+  });
+});
diff --git a/src/lib/security/captcha.ts b/src/lib/security/captcha.ts
new file mode 100644
index 0000000..ba103d0
--- /dev/null
+++ b/src/lib/security/captcha.ts
@@ -0,0 +1,121 @@
+import { getSecurityConfig } from './config';
+
+export interface CaptchaResult {
+  question: string;
+  answer: number;
+  hash: string;
+  timestamp: number;
+}
+
+function generateSimpleCaptcha(): CaptchaResult {
+  const num1 = Math.floor(Math.random() * 10) + 1;
+  const num2 = Math.floor(Math.random() * 10) + 1;
+  const answer = num1 + num2;
+  const question = `${num1} + ${num2} = ?`;
+
+  return {
+    question,
+    answer,
+    hash: '',
+    timestamp: Date.now(),
+  };
+}
+
+function generateMediumCaptcha(): CaptchaResult {
+  const operations = ['+', '-', '*'];
+  const operation = operations[Math.floor(Math.random() * operations.length)];
+  const num1 = Math.floor(Math.random() * 20) + 1;
+  const num2 = Math.floor(Math.random() * 10) + 1;
+
+  let answer: number;
+  let question: string;
+
+  switch (operation) {
+    case '+':
+      answer = num1 + num2;
+      question = `${num1} + ${num2} = ?`;
+      break;
+    case '-':
+      answer = num1 - num2;
+      question = `${num1} - ${num2} = ?`;
+      break;
+    case '*':
+      answer = num1 * num2;
+      question = `${num1} * ${num2} = ?`;
+      break;
+    default:
+      answer = num1 + num2;
+      question = `${num1} + ${num2} = ?`;
+  }
+
+  return {
+    question,
+    answer,
+    hash: '',
+    timestamp: Date.now(),
+  };
+}
+
+function generateComplexCaptcha(): CaptchaResult {
+  const num1 = Math.floor(Math.random() * 15) + 1;
+  const num2 = Math.floor(Math.random() * 10) + 1;
+  const num3 = Math.floor(Math.random() * 5) + 1;
+
+  const operations = ['+', '-', '*'];
+  const op1 = operations[Math.floor(Math.random() * operations.length)];
+  const op2 = operations[Math.floor(Math.random() * operations.length)];
+
+  let answer: number;
+  let question: string;
+
+  const temp1 = op1 === '+' ? num1 + num2 : op1 === '-' ? num1 - num2 : num1 * num2;
+  answer = op2 === '+' ? temp1 + num3 : op2 === '-' ? temp1 - num3 : temp1 * num3;
+
+  question = `(${num1} ${op1} ${num2}) ${op2} ${num3} = ?`;
+
+  return {
+    question,
+    answer,
+    hash: '',
+    timestamp: Date.now(),
+  };
+}
+
+function generateHash(answer: number, timestamp: number): string {
+  const secret = process.env.CAPTCHA_SECRET || 'default-secret-key';
+  const data = `${answer}-${timestamp}-${secret}`;
+  return Buffer.from(data).toString('base64');
+}
+
+export function generateCaptcha(complexity: 'simple' | 'medium' | 'complex' = 'medium'): CaptchaResult {
+  let captcha: CaptchaResult;
+
+  switch (complexity) {
+    case 'simple':
+      captcha = generateSimpleCaptcha();
+      break;
+    case 'complex':
+      captcha = generateComplexCaptcha();
+      break;
+    case 'medium':
+    default:
+      captcha = generateMediumCaptcha();
+      break;
+  }
+
+  captcha.hash = generateHash(captcha.answer, captcha.timestamp);
+  return captcha;
+}
+
+export function validateCaptcha(hash: string, answer: number, timestamp: number): boolean {
+  const config = getSecurityConfig();
+  const now = Date.now();
+  const ageMinutes = (now - timestamp) / (1000 * 60);
+
+  if (ageMinutes > config.captcha.expiryMinutes) {
+    return false;
+  }
+
+  const expectedHash = generateHash(answer, timestamp);
+  return hash === expectedHash;
+}