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Digital Signature

SMS + Face ID Signatures With a Hash-Chained Proof

Tested: one-time SMS code + biometrics, SHA-256 anchoring, hash-chained audit and public verify page — honest about QES.

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By Chegatta Team

1 min read

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The Real-World Context

Employment contracts need proof: who signed, what they signed, and that it never changed. A typed name at the bottom isn’t proof.

The Test Scenario

We created a fictional contract, hashed it SHA-256 on upload, requested signature, sent SMS one-time code to the employee’s verified phone, verified it, then Face ID on the registered device. We then tried to change one byte and re-verify.

How It Works (The Mechanics)

  1. Hash on upload — document SHA-256 anchored.
  2. OTP + biometrics — ContractOtpChallenge single-use SMS, expires in minutes, then FaceID/fingerprint on registered device + typed name.
  3. Hash chain + certificate — every event hash-chains the previous; Signing Certificate has public verify page with ID and hash.

The Results / What We Verified

  • SMS + biometrics created certificate, public page verified. Pass.
  • Hash re-verified at signing; one-byte change refused. Pass.
  • Chain intact across 128 events. Pass.

Honest caveat: This is advanced-seal evidence — strong for labour disputes. Qualified Electronic Signature (QES) needs a qualified TSP — we state that openly in digital-signature.mdx.

Call to Action

Sign inside the app your team already uses — Instant 2-Minute Setup • No Credit Card Required. Try Chegatta free at Chegatta.com.

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About Chegatta

Chegatta is a verified, compliant attendance platform for staffing agencies and businesses. Our team writes practical guides on attendance, payroll compliance and preventing time theft.

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