Implementing STIR/SHAKEN Attestation Verification for Inbound Call Authentication

How-To-Articles
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Implementing STIR/SHAKEN Attestation Verification for Inbound Call Authentication

What This Guide Covers

This guide details the architectural implementation and configuration required to validate STIR/SHAKEN digital signatures on inbound SIP traffic within Genesys Cloud CX. You will configure the telephony provider trust settings, enforce attestation level verification at the network edge, and implement routing logic that distinguishes between fully attested, partially attested, and non-attested calls. The end result is a hardened telephony perimeter that automatically rejects or flags spoofed traffic based on cryptographic verification, ensuring compliance with FCC mandates and reducing fraud exposure.

Prerequisites, Roles & Licensing

  • Licensing: Genesys Cloud CX 1 (or higher). STIR/SHAKEN support is native to the platform and does not require additional add-on licenses.
  • Roles & Permissions:
    • Telephony > Trunk > Edit: Required to modify trunk settings and enable signature verification.
    • Telephony > Provider > Edit: Required to manage provider trust configurations.
    • Administration > Users > Edit: Required if creating specific service accounts for API-driven verification logs.
  • External Dependencies:
    • A SIP trunk provider capable of passing STIR/SHAKEN attestation headers (e.g., Bandwidth, Twilio, Telnyx, or a direct carrier connection).
    • Access to the provider’s documentation regarding their Identity header implementation.
  • Knowledge Base: Familiarity with SIP signaling, RFC 8224 (STIR), and Genesys Cloud Architect flow logic.

The Implementation Deep-Dive

1. Configuring Provider Trust and Signature Verification

The foundation of STIR/SHAKEN verification in Genesys Cloud is not within the Architect flow itself, but in the Telephony Provider configuration. Genesys Cloud acts as the Verifying Service Provider (VSP). To verify the signature, Genesys must trust the certificate chain presented by the originating provider.

Navigate to Telephony > Providers in the Genesys Cloud Admin interface. Select the specific SIP trunk provider connected to your environment. If the provider is listed in Genesys’s pre-approved trust list, the system may automatically handle certificate pinning. However, for custom or direct carrier connections, you must manually configure the trust anchor.

The Trap: Ignoring Certificate Chain Validation

A common misconfiguration occurs when architects enable “Verify Signatures” on the trunk but fail to upload or validate the Intermediate CA certificates provided by their telephony partner. If the chain is broken, Genesys cannot validate the digital signature. Instead of rejecting the call, Genesys may default to treating the call as “Non-Attested” or, worse, fail open depending on the trunk’s failover configuration. This defeats the purpose of the security layer, allowing spoofed calls to pass through as unverified traffic rather than being blocked at the edge.

Architectural Reasoning: Edge vs. Application Layer Verification

Verification must occur at the network edge (the Trunk/Provider level) rather than inside an Architect flow. Processing cryptographic signatures requires access to the raw SIP headers before any media or signaling manipulation. If you attempt to verify signatures inside an Architect block using JavaScript or Scripting, you are working with sanitized or modified data that may have lost the necessary header integrity. By enforcing verification at the Provider level, Genesys Cloud performs the cryptographic check before the call enters your routing logic. This ensures that the Attestation Level variable available in Architect reflects a cryptographically verified state, not just a claimed value.

To configure this:

  1. Edit the Provider.
  2. Locate the STIR/SHAKEN section.
  3. Set Verify Incoming Signatures to Enabled.
  4. Select Reject Calls Without Signature if you wish to enforce strict compliance (blocking all non-attested traffic). Alternatively, select Allow but Flag to route non-attested calls to a specific handling queue for manual review.
  5. Upload the trusted CA certificates if your provider is not auto-trusted.

2. Routing Based on Attestation Levels

Once verification is enabled at the trunk level, Genesys Cloud exposes the attestation status as a dynamic variable within the Architect flow. This allows you to implement business logic that treats calls differently based on their trust score.

STIR/SHAKEN defines three levels of attestation:

  • A (Full): The caller is verified as the legitimate owner of the number. The provider has verified the call originates from an authorized endpoint.
  • B (Partial): The provider can verify the number was assigned to the caller, but cannot verify the caller is the authorized user (e.g., a reseller scenario).
  • C (Gateway): The provider cannot verify the caller’s identity or authorization. This is common for international calls or legacy SIP trunks.

The Trap: Over-Reliance on Attestation Level A

A frequent architectural error is routing all Level A calls directly to agents while blocking everything else. This creates a severe user experience degradation for legitimate callers who originate from VoIP providers that only support Level B or C attestation due to technical limitations or international routing. Blocking Level B/C traffic indiscriminately results in lost business and customer complaints. The correct approach is to treat Level A as “High Priority/Trusted” and Level B/C as “Standard/Scrutinized,” not “Blocked.”

Implementation Steps in Architect

  1. Open your Inbound Call Flow.
  2. Drag a Set Variable block immediately after the call enters the flow (before any IVR prompts).
  3. Create a new variable, e.g., call.attestation.level, and set its value to ${call.attestation.level}.
    • Note: The exact variable path may vary slightly by platform version, but typically resides under call.attestation.
  4. Add a Condition block to evaluate this variable.

Condition Logic Example:

IF ${call.attestation.level} equals "A"
  THEN Route to "Premium Support Queue" (or direct to agent)
ELSE IF ${call.attestation.level} equals "B"
  THEN Route to "Standard IVR"
ELSE IF ${call.attestation.level} equals "C"
  THEN Route to "Fraud Screening IVR"
ELSE (No Attestation/Failed Verification)
  THEN Play "Call Verification Failed" message and disconnect

Architectural Reasoning: Dynamic Routing and Cost Optimization

By routing Level A calls to premium queues, you reduce friction for trusted partners (e.g., banks, government agencies). By routing Level C calls to a screening IVR, you add a friction step that deters robocallers. Robocallers often use non-attested or spoofed numbers; adding a “Press 1 to continue” or a CAPTCHA-style audio challenge increases the cost of the attack. This architectural pattern leverages attestation not just for security, but for operational efficiency and cost control.

3. Handling Non-Attested and International Traffic

International calls often lack STIR/SHAKEN attestation because the originating country may not have implemented the framework. If you strictly reject non-attested calls, you will block all international inbound traffic.

The Trap: Global Blocking of Non-Attested Calls

Enabling “Reject Calls Without Signature” globally on the trunk without geographic exceptions will cause immediate service outages for international customers. This is a catastrophic failure mode in global deployments.

Solution: Geographic Exception Handling

Use the Call Information block to inspect the countryCode or callingPartyNumber area code before applying strict attestation rules.

  1. Add a Condition block before the attestation check.
  2. Check if the call originates from a region where STIR/SHAKEN is not mandated (e.g., specific countries outside the US/Canada).
  3. If the call is from an exempt region, bypass the attestation verification logic and route to standard handling.
  4. If the call is from a regulated region (e.g., US, Canada), proceed with the attestation-based routing defined in Step 2.

This hybrid approach ensures compliance with FCC regulations in the US while maintaining global accessibility.

Validation, Edge Cases & Troubleshooting

Edge Case 1: Signature Verification Failure Due to Clock Skew

The Failure Condition: Calls from a trusted provider are being rejected as “Invalid Signature” despite correct certificate configuration.

The Root Cause: STIR/SHAKEN signatures include a timestamp. If the clock on the Genesys Cloud edge servers and the originating provider’s signing server are not synchronized within a narrow window (typically 30-60 seconds), the signature is considered expired or not yet valid. This is common during daylight saving time transitions or if the provider’s infrastructure has poor NTP synchronization.

The Solution:

  1. Verify that your provider is using NTP (Network Time Protocol) to synchronize their servers.
  2. In Genesys Cloud, there is no user-configurable clock skew tolerance. However, you can temporarily switch the trunk setting from “Reject” to “Flag” to allow calls through while diagnosing.
  3. Contact the provider’s support team to confirm their signing server’s NTP status.
  4. Check Genesys Cloud status pages for any known issues with signature verification services.

Edge Case 2: Attestation Level Downgrade During SIP Trunking Hops

The Failure Condition: A call originates from a fully attested source (Level A) but arrives at Genesys Cloud as Level B or C.

The Root Cause: STIR/SHAKEN requires that if a service provider cannot verify the attestation of the previous hop, they must downgrade the attestation level. If your SIP trunk provider acts as an intermediary and does not have a direct trust relationship with the originator, they may downgrade the level to B or C. This is compliant behavior but results in a loss of trust granularity.

The Solution:

  1. Confirm with your SIP trunk provider whether they support “Passthrough” of attestation headers or if they re-sign calls.
  2. If they re-sign, ensure they have a direct peering agreement with the originator to maintain Level A.
  3. If they only support Level B/C for third-party traffic, adjust your Architect routing logic to treat Level B as “Trusted” for that specific provider.
  4. Use the call.attestation.originatingProvider variable (if available) to create provider-specific routing rules.

Edge Case 3: JavaScript Engine Timeout During Attestation Processing

The Failure Condition: Calls hang at the entry point of the Architect flow for 5-10 seconds before proceeding.

The Root Cause: If you are using complex JavaScript blocks to parse attestation headers or log verification details before routing, you may hit the JavaScript execution timeout limit. Genesys Cloud imposes strict timeouts on script execution to prevent flow blocking.

The Solution:

  1. Avoid heavy processing in the initial call entry path.
  2. Use native Genesys Cloud variables (call.attestation.level) instead of parsing raw SIP headers via JavaScript.
  3. If logging is required, use asynchronous logging via the Genesys Cloud API rather than synchronous blocks in the flow.
  4. Ensure that any condition blocks evaluating attestation levels are simple string comparisons, not complex regex or object manipulations.

Official References