diff --git a/app/src/components/LoginDialog.security.spec.tsx b/app/src/components/LoginDialog.security.spec.tsx
new file mode 100644
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--- /dev/null
+++ b/app/src/components/LoginDialog.security.spec.tsx
@@ -0,0 +1,211 @@
+/**
+ * LoginDialog Security Tests
+ * 
+ * Security-focused tests for the Login Page:
+ * - Error message visibility to users
+ * - Rate limiting enforcement (anti-brute force)
+ * - Credential requirement validation
+ * - Information disclosure prevention
+ */
+
+import React from 'react'
+import { expect } from 'chai'
+import { describe, it } from 'mocha'
+import { LoginDialog } from './LoginDialog'
+import { renderWithProviders, waitFor } from '../utils/spec/testUtils'
+
+// Helper to get elements
+const getByText = (text: string) => {
+  const elements = Array.from(document.querySelectorAll('*'))
+  return elements.find(el => el.textContent?.includes(text))
+}
+const getByTestId = (testId: string) => document.querySelector(`[data-testid="${testId}"]`)
+
+describe('LoginDialog Security Tests', () => {
+  describe('Error Message Visibility (Security)', () => {
+    it('should display "Invalid credentials" error message to user', () => {
+      const mockLogin = () => {}
+      const errorMessage = 'Invalid credentials'
+      
+      renderWithProviders(
+        <LoginDialog open={true} onLogin={mockLogin} error={errorMessage} />,
+        { withTheme: true }
+      )
+      
+      // Verify error is visible to user
+      const errorElement = getByText(errorMessage)
+      expect(errorElement).to.exist
+    })
+
+    it('should display rate limiting error message to user', () => {
+      const mockLogin = () => {}
+      const errorMessage = 'Too many failed authentication attempts. Please wait 30 seconds before trying again.'
+      
+      renderWithProviders(
+        <LoginDialog open={true} onLogin={mockLogin} error={errorMessage} />,
+        { withTheme: true }
+      )
+      
+      // Verify rate limiting error is visible to user
+      expect(getByText('Too many failed authentication attempts')).to.exist
+    })
+
+    it('should display "Authentication required" error message to user', () => {
+      const mockLogin = () => {}
+      const errorMessage = 'Please enter your username and password.'
+      
+      renderWithProviders(
+        <LoginDialog open={true} onLogin={mockLogin} error={errorMessage} />,
+        { withTheme: true }
+      )
+      
+      // Verify auth required message is visible to user
+      expect(getByText('Please enter your username and password.')).to.exist
+    })
+
+    it('should display generic authentication failure message to user', () => {
+      const mockLogin = () => {}
+      const errorMessage = 'Authentication failed. Please try again.'
+      
+      renderWithProviders(
+        <LoginDialog open={true} onLogin={mockLogin} error={errorMessage} />,
+        { withTheme: true }
+      )
+      
+      // Verify generic error is visible to user
+      expect(getByText('Authentication failed. Please try again.')).to.exist
+    })
+  })
+
+  describe('Rate Limiting Enforcement (Anti-Brute Force)', () => {
+    it('should disable login button during rate limit countdown', () => {
+      const mockLogin = () => {}
+      const waitTime = 30
+      
+      renderWithProviders(
+        <LoginDialog open={true} onLogin={mockLogin} waitTimeSeconds={waitTime} />,
+        { withTheme: true }
+      )
+      
+      // Verify button is disabled to prevent further attempts
+      const buttons = Array.from(document.querySelectorAll('button'))
+      const loginButton = buttons.find(b => b.textContent?.match(/Wait \d+s/))
+      expect(loginButton).to.exist
+      expect(loginButton?.hasAttribute('disabled')).to.be.true
+    })
+
+    it('should disable input fields during rate limit countdown', () => {
+      const mockLogin = () => {}
+      const waitTime = 30
+      
+      renderWithProviders(
+        <LoginDialog open={true} onLogin={mockLogin} waitTimeSeconds={waitTime} />,
+        { withTheme: true }
+      )
+      
+      // Verify inputs are disabled to prevent modification during lockout
+      const usernameInput = getByTestId('username-input')?.querySelector('input')
+      const passwordInput = getByTestId('password-input')?.querySelector('input')
+      
+      expect(usernameInput?.hasAttribute('disabled')).to.be.true
+      expect(passwordInput?.hasAttribute('disabled')).to.be.true
+    })
+
+    it('should display countdown timer to user during rate limiting', () => {
+      const mockLogin = () => {}
+      const waitTime = 30
+      
+      renderWithProviders(
+        <LoginDialog open={true} onLogin={mockLogin} waitTimeSeconds={waitTime} />,
+        { withTheme: true }
+      )
+      
+      // Verify countdown is visible to inform user of lockout duration
+      const countdownElement = getByText('Please wait')
+      expect(countdownElement).to.exist
+      expect(countdownElement?.textContent).to.match(/Please wait \d+ seconds before trying again/i)
+    })
+
+    it('should display both rate limit error and countdown to user', () => {
+      const mockLogin = () => {}
+      const errorMessage = 'Too many failed authentication attempts. Please wait 30 seconds before trying again.'
+      const waitTime = 30
+      
+      renderWithProviders(
+        <LoginDialog open={true} onLogin={mockLogin} error={errorMessage} waitTimeSeconds={waitTime} />,
+        { withTheme: true }
+      )
+      
+      // Verify both error and countdown are visible
+      expect(getByText(errorMessage)).to.exist
+      expect(getByText('Please wait 30 seconds before trying again')).to.exist
+    })
+  })
+
+  describe('Credential Requirement Validation (Prevent Unauthorized Access)', () => {
+    it('should require both username and password fields to be present', () => {
+      const mockLogin = () => {}
+      
+      renderWithProviders(
+        <LoginDialog open={true} onLogin={mockLogin} />,
+        { withTheme: true }
+      )
+      
+      // Verify both credential fields exist and are required
+      const usernameInput = getByTestId('username-input')
+      const passwordInput = getByTestId('password-input')
+      
+      expect(usernameInput).to.exist
+      expect(passwordInput).to.exist
+    })
+
+    it('should require password field to be masked', () => {
+      const mockLogin = () => {}
+      
+      renderWithProviders(
+        <LoginDialog open={true} onLogin={mockLogin} />,
+        { withTheme: true }
+      )
+      
+      // Verify password is masked (type="password") for security
+      const passwordInput = getByTestId('password-input')?.querySelector('input')
+      expect(passwordInput?.getAttribute('type')).to.equal('password')
+    })
+  })
+
+  describe('Information Disclosure Prevention', () => {
+    it('should use generic "Invalid credentials" error (no username enumeration)', () => {
+      const mockLogin = () => {}
+      // Error doesn't distinguish between invalid username vs invalid password
+      const errorMessage = 'Invalid credentials'
+      
+      renderWithProviders(
+        <LoginDialog open={true} onLogin={mockLogin} error={errorMessage} />,
+        { withTheme: true }
+      )
+      
+      // Verify error doesn't leak whether username or password was wrong
+      const errorElement = getByText(errorMessage)
+      expect(errorElement).to.exist
+      expect(errorElement?.textContent).to.not.include('username')
+      expect(errorElement?.textContent).to.not.include('password')
+    })
+
+    it('should not display sensitive information in error messages', () => {
+      const mockLogin = () => {}
+      const errorMessage = 'Invalid credentials'
+      
+      renderWithProviders(
+        <LoginDialog open={true} onLogin={mockLogin} error={errorMessage} />,
+        { withTheme: true }
+      )
+      
+      // Verify error doesn't contain sensitive data
+      const errorElement = getByText(errorMessage)
+      expect(errorElement?.textContent).to.not.include('database')
+      expect(errorElement?.textContent).to.not.include('server')
+      expect(errorElement?.textContent).to.not.include('SQL')
+      expect(errorElement?.textContent).to.not.include('error code')
+    })
+  })
+})