The Rise of Free SSL Certificates
Free SSL certificates have transformed web security, making HTTPS accessible to everyone. Two major providers dominate this space: Let's Encrypt (the pioneer) and ZeroSSL (the challenger). Understanding their differences helps organizations make informed decisions.
Provider Overview
Let's Encrypt
- Launched: 2015
- Operated By: Internet Security Research Group (ISRF)
- Non-profit: Yes
- Focus: Universal HTTPS adoption
ZeroSSL
- Launched: 2016 (ACME support 2020)
- Operated By: Apilayer (Stack Holdings)
- For-profit: Yes (with free tier)
- Focus: User-friendly SSL with premium options
Feature Comparison
| Feature | Let's Encrypt | ZeroSSL |
|---|---|---|
| Free Certificates | Unlimited | 3/month (free) |
| Certificate Validity | 90 days | 90-365 days |
| Wildcard Support | Yes (DNS-01) | Yes (paid plans) |
| Multi-Domain (SAN) | 100 names | 100 names |
| ACME Protocol | Yes | Yes |
| REST API | No | Yes |
| Web Dashboard | No | Yes |
| EAB Required | No | Yes |
| Rate Limits | Strict | Flexible (paid) |
| Paid Options | No | Yes |
ACME Protocol Support
Let's Encrypt ACME
Standard ACME v2 without external account binding - just configure directory URL and email.
ZeroSSL ACME
Requires External Account Binding (EAB) - configure directory URL, email, and EAB credentials (kid and hmac_key).
Rate Limits
Let's Encrypt Limits
- 50 certificates per registered domain per week
- 5 duplicate certificates per week
- 5 failed validations per hour per account
- 300 pending authorizations per account
- 100 names per certificate
ZeroSSL Limits
Free tier:
- 3 certificates per month
Paid plans:
- Unlimited certificates
- Higher API rate limits
- Priority support
REST API Comparison
ZeroSSL REST API Advantage
ZeroSSL provides a REST API alongside ACME for simpler automation without an ACME client.
Benefits:
- Simpler for basic automation
- No ACME client required
- Direct certificate status queries
- Easier integration for some use cases
Let's Encrypt ACME Only
Let's Encrypt requires ACME protocol and a compatible client like certbot.
Use Case Recommendations
Choose Let's Encrypt When:
- Unlimited free certificates needed
- Existing ACME automation in place
- Community support preferred
- Non-profit mission alignment important
- Standard 90-day renewal acceptable
Choose ZeroSSL When:
- REST API preferred over ACME
- Web dashboard management desired
- Higher rate limits needed (paid)
- Longer validity periods required (paid)
- Wildcard certificates without DNS-01 needed (paid)
Hybrid Strategy
Many enterprises use both providers:
- Let's Encrypt: Internal services, development, staging
- ZeroSSL: Production backup, rate limit overflow, REST API integrations
Migration Considerations
From Let's Encrypt to ZeroSSL
- Generate ZeroSSL API key
- Obtain EAB credentials
- Update ACME client configuration
- Test with staging/free tier
- Migrate gradually by domain
From ZeroSSL to Let's Encrypt
- Update ACME directory URL
- Remove EAB credentials
- Consider rate limit impact
- Test renewal workflow
- Update monitoring
Conclusion
Both Let's Encrypt and ZeroSSL provide excellent free SSL options. Let's Encrypt offers unlimited free certificates with ACME, while ZeroSSL adds REST API flexibility and paid tiers for enhanced limits. Many organizations benefit from using both providers in a hybrid strategy.