Blending encryption, authentication, and seamless user experience>
Encrypted Coordinate-Based Digital Signatures
01/06 Project Context
In today’s digital-first world, documents need to be signed quickly, securely, and in a way that feels natural. Traditional digital signature methods often fall short: simple image uploads or click-to-sign systems either feel impersonal or open the door to potential misuse.
This multinational faced a common challenge: engineers needed to sign documents digitally, but I had to ensure that each signature was both authentic and secure. I also had to comply with international data protection regulations like GDPR, CCPA, and TISAX, which meant minimizing the storage of sensitive personal data.
Summary
- Make drawing a signature feel fluid and pen-like.
- Prevent stored signatures from being stolen or reused.
- Ensure compliance with international data protection standards (GDPR, CCPA, TISAX).
- Confirm the signer’s identity beyond just a graphic of their handwriting.
02/06 Challenges
Implementing a secure and user-friendly digital signature system involved addressing multiple intertwined challenges. I needed to create a natural signing experience, ensure the security of signature data, comply with international regulations like GDPR, CCPA, and TISAX, and verify that only the authorized user could apply their signature. Each of these aspects shaped the design decisions from the very beginning.
UX
Users need a natural, pen-like experience when signing digitally. Capturing smooth strokes and simulating pressure was crucial to make signing feel effortless.
Security
Storing signatures as images is risky. The challenge was to encrypt each stroke securely to ensure coordinates cannot be intercepted or tampered with.
Compliance
International standards like GDPR, CCPA, and TISAX require strict handling of personal data. The system had to minimize sensitive storage while remaining fully auditable.
Authentication
Ensuring that only the intended user can apply their signature was critical. MFA integration and secure key reconstruction addressed this challenge.
03/06 Solution
To overcome the challenges, I designed a layered solution that blends smooth, realistic rendering with robust encryption and secure authentication. By capturing the essence of a signature through coordinates, simulating pressure, and smoothing strokes with Bezier curves, the system ensures an authentic and fully compliant signing experience.
Bezier Curve Smoothing
Converts jagged mouse or touch input into smooth, natural lines, ensuring the signature looks authentic and fluid.
Pressure Simulation
Stroke thickness is dynamically calculated from drawing speed and point spacing, mimicking real handwriting pressure for a more realistic signing experience.
Coordinate Mapping
Each signature is captured as a series of coordinates instead of storing images, making it secure, encrypted, and compliant with data protection standards like GDPR and CCPA.
04/06 Technical Aspects
The security and integrity of every signature rely on multiple technical layers. Encryption ensures that the signature coordinates are unreadable to anyone without proper access, while dynamic key management prevents permanent storage of sensitive keys. Multi-factor authentication and on-demand key reconstruction guarantee that only the authorized user can apply their signature, and the signature is only re-rendered after successful verification.
AES-256
Encrypts signature coordinates using a military-grade standard. Keeps the signature unreadable without the encryption key.
SHA-512
Derives strong keys from user-specific data. Provides high resistance against brute-force attacks.
HMAC + PBKDF2 + Pepper
Generates secure keys by combining a hash-based code with a password-derived function and an additional secret. Strengthens encryption against unauthorized access.
Initialization Vector (IV)
Randomizes each encryption session so that identical data produces different encrypted outputs. Adds an extra layer of security.
Dynamic Key Management
Keys are generated on-demand using user-specific information and system context. No permanent key is ever stored, ensuring maximum security.
Authentication & Verification
- MFA via Microsoft Authenticator: Each signing request requires device confirmation.
- On-Demand Key Reconstruction: Keys dynamically generated from user data, AD info, and system context.
- Secure Re-rendering: Only after MFA and decryption, the signature coordinates are redrawn on the document.
05/06 Compliance Alignment
GDPR (EU)
Requires minimizing personal data storage and protecting user information. The system stores only encrypted coordinates, never biometric images, ensuring privacy by design.
CCPA (California)
Enforces the right to privacy and secure handling of personal identifiers. Only encrypted coordinates can be used, and MFA ensures that only the authorized user can sign.
TISAX (Automotive)
Mandates secure handling of sensitive information with access control and encryption. Signatures are encrypted at capture, in storage, and during transmission, with MFA protecting access.
06/06 Outcome & Reflection
- No reusable images: Signatures can’t be stolen or impersonated via image files.
- Compliance-ready: Coordinate system + encryption + MFA aligns with GDPR, CCPA, TISAX.
- Enterprise-grade security: Security extends beyond signature—it’s identity-verified.
- Natural user experience: Smooth, pen-like rendering made adoption frictionless.
Lessons Learned
- Compliance considerations often dictate design choices as much as security.
- Image-based signatures are risky from both security and regulatory standpoints.
- Encrypted coordinate data ensures security + compliance simultaneously.
- Strong cryptography + MFA builds trust for both users and auditors.
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