A voice call can travel across multiple networks and still fail authentication before reaching its destination. The reason may be hidden in a single SIP Identity header containing information about the caller, the signing certificate and the digital signature.
For telecom operators, diagnosing these failures requires more than checking whether a call was marked as verified or unverified. STIR/SHAKEN Identity Header analysis provides visibility into the authentication data behind a call, helping technical teams identify inconsistencies, certificate problems and configuration errors. It turns a confusing verification result into information that network engineers can investigate and act upon.
Understanding the Role of the Identity Header in Voice Authentication
The SIP Identity header is a central component of STIR/SHAKEN. It carries a digitally signed PASSporT token that allows the receiving service provider to verify the calling identity information asserted by the originating provider.
What information does the header contain?
A typical STIR/SHAKEN Identity header includes several important elements:
PASSporT token: A digitally signed token containing information about the call.
info: Identifies the URL where the originating provider's certificate can be retrieved.
alg: Specifies the cryptographic algorithm used for the signature.
ppt: Identifies the PASSporT extension or token type. For SHAKEN this is typically shaken.
The PASSporT itself contains a header and payload as well as a digital signature. Its decoded information can reveal the attestation level, originating telephone number, destination number, issue time and origination identifier.
These fields provide the foundation for investigating authentication problems. Instead of treating the Identity header as an opaque string, engineers can examine its individual components.
Why analysis matters
Think of the Identity header as a digital record attached to a call. If the record contains an incorrect destination number or references an unavailable certificate, the verification process may fail even when the call itself is legitimate.
Understanding the header helps operators identify where the authentication process is breaking down.
Identify PASSporT Token Errors Before They Become Network Problems
PASSporT validation involves checking the token's structure, contents and signature. A failure in any of these areas can prevent successful caller authentication.
Inspect the token structure
A PASSporT token generally consists of three Base64URL-encoded sections separated by two periods:
Header.Payload.Signature
The header identifies the token type and cryptographic algorithm while the payload contains call-specific information. The signature protects the token's contents against unauthorised modification.
Decoding the token allows engineers to inspect these values without having to interpret the encoded string manually.
Check the important payload fields
Several fields are particularly useful during troubleshooting:
orig: The originating telephone number represented in the token.
dest: The destination telephone number or numbers.
iat: The time when the token was issued.
attest: The attestation level assigned by the originating provider.
origid: A unique origination identifier associated with the call.
For example, imagine a call where the SIP From header contains one telephone number but the PASSporT orig field contains another. This inconsistency can cause verification to fail because the signed identity information does not match the call signalling.
Similarly, an incorrect destination number in the token can indicate a call-routing or identity-generation problem.
Diagnose Certificate and Signature Verification Failures
A correctly formatted PASSporT does not automatically mean that a call will pass authentication. The receiving network must also retrieve and trust the associated certificate and verify the digital signature.
Investigate the certificate URL
The info parameter in the Identity header points to the certificate repository location. The PASSporT header also includes an x5u parameter identifying the certificate URL.
If the certificate cannot be retrieved because of an unavailable server, incorrect URL or network timeout, verification may fail.
Engineers should inspect:
Whether the certificate URL is accessible.
Whether the certificate belongs to the expected originating provider.
Whether the certificate is within its validity period.
Whether the certificate chains to a trusted authority.
Whether the certificate has been revoked or is otherwise unacceptable under the verification policy.
Examine the cryptographic signature
The signature is generated using the originating provider's private key and verified using the public key contained in the corresponding certificate.
If the token has been modified after signing or the wrong public key is used during verification, the signature check will fail.
This is why certificate and key management must remain consistent across the authentication process. A certificate rotation that is not reflected correctly in signing infrastructure can create avoidable verification problems.
Use Identity Header Analysis to Pinpoint Common Authentication Failures
A verification failure is a result. Identity Header analysis helps engineers investigate the reason behind it.
Common failure scenarios
Missing Identity header: A call arrives without the expected Identity header. This may indicate that the originating network did not sign the call or that an intermediate network removed the header.
Stale timestamp: The iat field indicates when the PASSporT was created. A token that falls outside the permitted time window may be rejected. Engineers should compare the token timestamp with the verification time and investigate clock synchronisation or call-processing delays.
Certificate retrieval failure: The certificate URL cannot be reached or returns an error. The team should check repository availability, URL configuration and network connectivity.
Untrusted certificate: The certificate is available but the verification service does not recognise or trust its issuing authority or credentials.
Invalid signature or mismatched call details: The signature fails verification or the orig and dest values do not match the corresponding SIP signalling information.
These failure categories are reflected in STIR/SHAKEN verification practices documented by TransNexus. Its technical guidance describes response codes including 403 for stale date, 436 for certificate retrieval problems, 437 for unsupported credentials and 438 for invalid Identity headers.
Why this makes troubleshooting faster
Without structured analysis, an engineer may need to inspect several SIP messages, certificate files and application logs to isolate a problem. Decoding the header first provides a more focused starting point and helps narrow down which component needs further investigation.
Improve Troubleshooting with Automated Identity Header Inspection
Manual inspection is useful for individual cases but becomes inefficient when telecom providers handle large volumes of authentication events.
From manual decoding to API-driven diagnostics
Automated Identity Header inspection can help technical teams decode PASSporT tokens, extract certificate URLs and examine key authentication fields through a repeatable workflow.
For example, PeeringHub provides a STIR/SHAKEN Identity Header Parser that allows users to submit a SIP Identity header and inspect:
Decoded PASSporT header and payload information.
Attestation level and origination identifier.
Originating and destination telephone numbers.
Certificate URL extracted from the token.
Algorithm and signature validation status.
PeeringHub also provides a public STI/SHAKEN API for Identity Header decoding and validation. These capabilities can help developers and network engineers incorporate authentication checks into diagnostic tools and operational workflows.
Why automation matters
Consider a service provider investigating repeated authentication failures across several network routes. Instead of manually decoding every token, an integrated validation workflow can make it easier to collect consistent information and identify recurring problems.
Automation does not replace detailed network investigation. It reduces repetitive inspection and helps engineers focus on the underlying issue.
Comparing Identity Header Analysis Capabilities Across Telecom Solutions
Different telecom platforms approach STIR/SHAKEN verification and troubleshooting from different operational perspectives. The important distinction is whether a provider needs a dedicated inspection utility, a broader authentication platform or an integrated call analytics solution.
PeeringHub: Dedicated header inspection and developer APIs
PeeringHub offers a dedicated Identity Header Parser alongside its certificate inspection and validation utilities. Its public API supports header decoding and validation as well as certificate inspection and OCN lookup.
Its ACME API separately supports certificate issuance, renewal and revocation. This combination is relevant to providers that want accessible diagnostic tools alongside certificate lifecycle automation.
TransNexus: Verification services and detailed error handling
TransNexus documents a STIR/SHAKEN verification service that checks Identity header formatting, PASSporT contents, certificate validity and digital signatures. Its technical documentation also explains verification response codes and how results can be used by service providers.
This approach is relevant to operators looking for verification services and call-handling capabilities within a broader STIR/SHAKEN solution.
TNS: Authentication with call analytics
TNS offers STIR/SHAKEN capabilities through its Call Guardian solutions. Its published product information describes combining caller authentication with real-time analytics to help assess both the validity and potential intent of calls.
This is relevant to providers looking beyond token inspection towards wider call-protection and reputation capabilities.
Choosing the right approach
The right solution depends on the operational requirement:
Header-level diagnostics: Look for tools that decode PASSporT tokens and expose individual fields.
Certificate troubleshooting: Check certificate retrieval, validity and trust information.
Automated integration: Evaluate API access and compatibility with existing systems.
Call verification: Determine whether the platform supports end-to-end verification and useful error reporting.
Fraud analysis: Consider whether additional traffic analytics and reputation information are required.
These capabilities are complementary rather than identical. A header parser helps explain authentication data while a verification platform processes calls and an analytics system evaluates broader call behaviour.
Build a More Reliable Voice Authentication Troubleshooting Process
Identity Header analysis becomes most valuable when it is part of a consistent operational procedure rather than an occasional debugging activity.
Establish a practical diagnostic workflow
Telecom engineering teams can follow a repeatable sequence:
Capture the SIP INVITE and locate the Identity header.
Decode the PASSporT token and inspect its header and payload.
Compare orig and dest values with the relevant SIP signalling fields.
Review the iat timestamp and attestation information.
Retrieve the certificate using the referenced URL.
Inspect certificate validity and trust information.
Validate the digital signature and investigate the reported error.
Record the findings and check whether the issue affects other calls or routes.
This process creates a clearer connection between the authentication result and the underlying technical cause.
Make certificate management part of the process
Troubleshooting should not stop once a failed certificate is identified. Providers should also review certificate renewal schedules, repository availability, private-key access controls and configuration consistency.
PeeringHub's certificate management services and API workflows can support this operational requirement by helping providers manage certificate-related tasks alongside their broader STIR/SHAKEN infrastructure.
Conclusion: Better Visibility Leads to Better Voice Authentication
Voice authentication failures are not always caused by complicated network problems. Sometimes the explanation is contained in the Identity header itself: a mismatched telephone number, an outdated timestamp, an inaccessible certificate or an invalid digital signature.
By analysing PASSporT contents and certificate information, telecom providers can move beyond basic failure notifications and identify the technical causes behind authentication issues. Automated parsing and validation make this process more consistent while API integration helps teams incorporate diagnostics into their existing systems.
PeeringHub brings together Identity Header decoding, signature validation, certificate inspection and developer-focused STIR/SHAKEN APIs to support these workflows.
Explore PeeringHub at https://www.peeringhub.io/ and discover how its Identity Header Parser, public STI/SHAKEN API and certificate management capabilities can help simplify voice authentication diagnostics!
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