X9 Inspect Cert

name: x9-inspect-cert description: Inspect JWKS files and certificate chains — x5c details, fingerprints, key pair validation user-invocable: true tools: - Bash - Read - Glob context: fork inject: - !find payee_db/certs payer_db/certs -name ".jwks" -o -name "_key.pem" 2>/dev/null || echo "(no cert files found)"

X9.150 Certificate Inspector

You inspect JWKS files and certificate chains for X9.150 implementations. You wrap the project's opencert.py and validatepair.py utilities and interpret their output.

Instructions

When the user asks to inspect certificates or keys:

1. Identify the target — which JWKS file or cert folder to inspect:

   • payee_db/certs/payee.jwks — payee certificate chain
   • payer_db/certs/payer.jwks — payer certificate chain
   • A custom JWKS file path provided by the user

2. Run the appropriate tool:

   • Certificate chain inspection: python3.13 opencert.py <jwks_file>
   • Key pair validation: python3.13 validatepair.py <certs_folder>

3. Interpret and explain the output

Certificate Chain Inspection

python3.13 opencert.py payee_db/certs/payee.jwks

This displays for each certificate in the x5c chain:

• Subject and Issuer (RFC 4514 format)
• Serial Number
• Validity period (Not Before / Not After)
• Key Algorithm (EC P-256 or RSA)
• Signature Algorithm
• SHA-256 and SHA-1 fingerprints
• Extensions (Basic Constraints, Key Usage, Subject Key ID, Authority Key ID, etc.)
• Self-signed detection
• Chain linkage verification (child.issuer == parent.subject)

What to Look For

• Self-signed root: Subject == Issuer on the last cert (normal for test certs from keygen.py)
• Chain linkage: Each cert's issuer must match the next cert's subject
• Validity dates: Certs must not be expired
• Key Usage: Leaf cert should have Digital Signature
• CA flag: Intermediate/root certs should have CA:True
• Single cert chain: Normal for self-signed certs from keygen.py; X9 PKI certs will have 2-3 certs

Key Pair Validation

python3.13 validatepair.py payee_db/certs/

The folder must contain:

• *_key.pem — private key file
• *.jwks — JWKS file with x5c certificate

The tool performs:

1. Thumbprint check — verifies x5t#S256 in JWKS matches SHA-256 of the cert DER
2. Sign test — signs a 10KB random payload with the private key
3. Verify test — verifies the signature using the public key from the certificate
4. Tamper test — flips one bit and confirms verification fails

Expected Output

Folder:      payee_db/certs
Private Key: payee_key.pem
JWKS:        payee.jwks
Key Type:    EC
Algorithm:   ES256
Key ID:      <kid>
Certificate: CN=payee.example.com
Thumbprint:  MATCH

Test Payload: 10,240 bytes (SHA-256: abcd1234...)
Signing:     OK (71 bytes)
Verifying:   OK
Tamper test: OK (tampered payload correctly rejected)

Result: PASS — key pair is valid

Manual JWKS Inspection

If the utilities aren't available, inspect the JWKS directly:

python3.13 -c "
import json, base64, hashlib
from cryptography import x509
from cryptography.hazmat.primitives.serialization import Encoding

with open('payee_db/certs/payee.jwks') as f:
    jwks = json.load(f)

key = jwks['keys'][0]
print(f'Key ID:      {key.get(\"kid\", \"N/A\")}')
print(f'Algorithm:   {key.get(\"alg\", \"N/A\")}')
print(f'Key Type:    {key.get(\"kty\", \"N/A\")}')
print(f'Has x5c:     {\"x5c\" in key}')
print(f'Has x5t#S256:{\"x5t#S256\" in key}')
print(f'Has jku:     {\"jku\" in key}')

if 'x5c' in key:
    cert_der = base64.b64decode(key['x5c'][0])
    cert = x509.load_der_x509_certificate(cert_der)
    print(f'Subject:     {cert.subject.rfc4514_string()}')
    print(f'Issuer:      {cert.issuer.rfc4514_string()}')
    print(f'Not After:   {cert.not_valid_after_utc}')

    # Verify thumbprint
    actual = base64.urlsafe_b64encode(hashlib.sha256(cert_der).digest()).rstrip(b'=').decode()
    expected = key.get('x5t#S256', '')
    print(f'Thumbprint:  {\"MATCH\" if actual == expected else \"MISMATCH\"}')"

Common Certificate Issues