Blog | G5 Cyber Security

Security Codes vs Links: Email Authentication

G5 Cyber Security

TL;DR

Sending security codes via email is generally more secure than clickable links for user authentication. Links are vulnerable to phishing and man-in-the-middle attacks, while codes add an extra layer of verification. However, both methods require careful implementation to protect users.

Why Security Codes Are Better

  1. Phishing Resistance: Clickable links can be easily disguised in phishing emails. Users might click a malicious link thinking it’s legitimate. A security code requires the user to actively enter it on the correct website, reducing this risk.
  2. Man-in-the-Middle (MitM) Protection: MitM attacks intercept communication between the user and server. With links, an attacker can redirect the user to a fake login page. Codes are less susceptible as they’re typically time-sensitive and tied to the specific session.
  3. Reduced Link Spoofing: Attackers can create convincing URLs that look like your website’s. Security codes don’t rely on URL accuracy.

Why Links Are Less Secure

  1. Phishing Attacks: The biggest risk. A well-crafted email with a fake link can trick users into entering their credentials on a malicious site.
  2. URL Manipulation: Attackers can shorten or obfuscate links to hide the true destination.
  3. Browser Redirection Vulnerabilities: Some browsers might allow attackers to redirect links even if the user is cautious.

Implementing Security Code Authentication

  1. Generate a Random Code: Use a cryptographically secure random number generator. Example (Python): 
    import secrets
random_code = secrets.token_hex(4)
print(random_code)
  2. Store the Code Temporarily: Associate the code with the user’s session in your database, along with a timestamp.
  3. Send the Email: Send an email containing *only* the security code. Avoid any links.
  4. Verify the Code: When the user enters the code on your website:
    • Check if the code exists in your database.
    • Check if the code has expired (typically 5-10 minutes).
    • If valid, authenticate the user and invalidate the code.

Implementing Link Authentication (if you must)

If you absolutely need to use links, take these precautions:

  1. Unique Tokens: Use a unique, unpredictable token in the link instead of directly passing user information.
  2. Expiration Times: Links should expire very quickly (e.g., within 1-2 minutes).
  3. HTTPS Only: Ensure your entire website uses HTTPS to prevent MitM attacks.
  4. Domain Verification: Use SPF, DKIM, and DMARC records to verify that emails are genuinely from your domain.
  5. Clear Instructions: Tell users *exactly* what the link is for and warn them about phishing attempts.

Additional Security Considerations

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