# 12. Comparisons & Obsolescence

- [12.1 Password-Based Authentication](/12.-comparisons-and-obsolescence/12.1-password-based-authentication.md)
- [12.2 OTP, SMS, and Authenticator Apps](/12.-comparisons-and-obsolescence/12.2-otp-sms-and-authenticator-apps.md)
- [12.3 Static API Keys & Service Secrets](/12.-comparisons-and-obsolescence/12.3-static-api-keys-and-service-secrets.md)
- [12.4 Custodial Payment Systems](/12.-comparisons-and-obsolescence/12.4-custodial-payment-systems.md)
- [12.5 Smart-Contract–Centric Web3 Stacks](/12.-comparisons-and-obsolescence/12.5-smart-contract-centric-web3-stacks.md)
- [12.6 “Zero Trust” (Policy-Heavy) Systems](/12.-comparisons-and-obsolescence/12.6-zero-trust-policy-heavy-systems.md)