SealSignature: Enterprise Document Signing at SMB Prices

Built a legally-compliant electronic signature platform that delivers enterprise-grade security at 20x lower cost than DocuSign.

The Challenge

Electronic signatures have become essential for business, but the market leaders price out small businesses and nonprofits. DocuSign starts at $10/month for just 5 documents. SignNow, HelloSign, and others follow similar pricing models that punish irregular usage.

For a freelancer who needs to sign one contract a month, or a small nonprofit that processes volunteer agreements seasonally, these subscription models make no sense. They end up paying enterprise prices for occasional use.

The technical challenge was equally demanding: building legally-valid electronic signatures requires compliance with ESIGN Act/UETA, proper cryptographic implementation, comprehensive audit trails, and trusted certificate authorities. Most “signature” apps just capture drawings – they’re not legally defensible.

The Solution

SealSignature was built from the ground up as a security-first document signing platform that prioritizes legal validity over flashy features.

Core Architecture: Python 3.12 with FastAPI provides async performance and automatic API documentation. React with Vite and Tailwind delivers a fast, modern frontend. PostgreSQL handles data with streaming replication for reliability.

Cryptographic Foundation: Using pyHanko (MIT-licensed), we implemented PAdES-T compliant signatures with RFC 3161 timestamps. Signing keys never leave AWS KMS – hardware-backed security at $5/month instead of expensive HSMs. Documents are encrypted at rest using S3 SSE-KMS.

Legal Compliance: Every signing action generates a cryptographically-chained audit trail with UTC timestamp, IP address, user agent, and document hash (SHA-256). GlobalSign provides AATL membership, meaning signatures are automatically trusted in Adobe Acrobat and Reader.

Usage-Based Pricing: $0.50 per document or $5/month unlimited. No commitment, no penalties for light usage. Stripe handles billing with full usage tracking.

The Results

• 20x cost reduction compared to DocuSign’s entry tier
• 100% legal validity – PAdES-T signatures pass validation in Adobe, courts, and regulatory review
• 12-week MVP delivery from concept to production-ready backend
• Zero security incidents – defense-in-depth architecture with no secrets in code
• Comprehensive audit trails with hash-chain integrity verification

Technologies Used

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