Aadhaar Authentication SHA-256 Migration Guide
A practical engineering guide to UIDAI's 2026 SHA-256 requirement for licensed Aadhaar authentication ecosystems, plus unique identifiers and rollout checks.
UIDAI’s Circular 4 of 2026 discontinued acceptance of SHA-1 after 30 June 2026 for the Aadhaar authentication ecosystem covered by the circular. Authentication entities should use SHA-2 signing certificates and SHA-256 for request hashing. If your integration still assumes that changing a certificate file is the entire migration, it deserves a deeper review.
This article is an engineering checklist, not legal advice. It applies to authorized Aadhaar authentication participants and their approved technology chains. It does not turn an ordinary application into an AUA, KUA, Sub-AUA, or Sub-KUA, and NamoID does not claim those roles here.
First identify which Aadhaar flow you use
Online Aadhaar authentication and offline Aadhaar verification are different systems. Online authentication involves licensed entities, UIDAI-defined requests, and the relevant authentication infrastructure. Offline e-KYC uses artifacts the resident can share without an online authentication request.
Do not apply an online-authentication circular blindly to every feature that contains the word “Aadhaar.” Start with your contracts, operating model, and the actual request path. If you verify resident-shared XML or QR artifacts, use our separate Aadhaar offline e-KYC XML guide. For product selection, see Aadhaar, DigiLocker, and offline KYC.
What Circular 4 changes
The migration has two connected concerns:
- The certificate used in the applicable signing chain should use SHA-2 rather than SHA-1.
- Authentication requests should use SHA-256 instead of SHA-1 for the relevant request hashing requirement.
These are not interchangeable. A SHA-256 certificate does not prove that the application generated every required digest correctly. Likewise, updating a digest algorithm while continuing to deploy an obsolete certificate chain leaves the migration incomplete.
Create an inventory that follows the request from the application to the final gateway. Include application libraries, signing services, hardware security modules, proxies, vendor SDKs, certificate stores, test environments, and disaster-recovery systems. Record the owner and deployed version for every component.
Verify the bytes sent over the wire
Crypto migrations often fail at serialization boundaries. The application may hash a different byte representation than the verifier expects because of XML canonicalization, encoding, whitespace, or library defaults.
Build known-answer tests from approved specifications or partner test environments. Your tests should verify:
- The precise bytes used as input to SHA-256.
- The digest and signature algorithms selected by configuration.
- Certificate chain validation and expiry handling.
- Request construction after every SDK or XML-library upgrade.
- Negative cases for SHA-1, altered payloads, expired certificates, and invalid signatures.
Inspect algorithm identifiers in the final serialized request rather than relying only on a configuration screen. Avoid logging Aadhaar numbers, biometrics, OTPs, demographic data, complete signed payloads, or private key material while debugging. Use synthetic identities and redacted diagnostics.
Do not keep a silent SHA-1 fallback
A compatibility fallback can undo the migration. If the preferred SHA-256 path fails and the application silently retries with SHA-1, operational dashboards may look healthy while non-compliant traffic continues.
Fail closed for disallowed algorithms. Alert on attempts to select SHA-1, identify the calling component, and remediate that component. If a partner environment is not ready, resolve it through the approved ecosystem process rather than weakening production behavior.
Add unique identifiers to the same review
UIDAI Circular 1 of 2026 addresses unique identifiers for Aadhaar-based authentication transactions. The goal is to distinguish schemes, departments, or use cases that may otherwise share an AUA, KUA, Sub-AUA, or Sub-KUA code. That improves auditability, fraud detection, monitoring, and performance analysis.
Treat this as structured transaction context, not a free-form marketing label. Establish who assigns each identifier, where it enters the request, how it is validated, and how it appears in privacy-conscious audit records. Test that identifiers cannot be accidentally reused across schemes or omitted by a downstream adapter.
Roll out with evidence
Use a controlled migration sequence:
- Confirm the official requirements with your compliance team and authorized ecosystem partners.
- Rotate certificates and validate the complete trust chain in a non-production environment.
- Deploy SHA-256 request generation with known-answer and negative tests.
- Verify unique-identifier routing for each applicable scheme or department.
- Run a limited production rollout with failure-rate and algorithm telemetry.
- Remove SHA-1 code paths, expired certificates, and emergency flags after verification.
- Save evidence: approvals, certificate fingerprints, test results, deployment records, and monitoring screenshots.
Operational evidence matters because a repository search cannot prove what a gateway actually received. Your final sign-off should connect source configuration, deployed artifacts, and observed transactions.
NamoID helps Indian teams design authentication and authorization boundaries around their applications. For Aadhaar-related architectures, we can help separate general application identity from regulated verification flows and review the integration boundary. Send a message in the NamoID Slack community for an early response; final eligibility and compliance decisions must still come from UIDAI and your authorized partners.