S3 Troubleshooting playbook
Needs: Supporter
From a symptom (response code, HSM error, KCV mismatch, MAC failure) to the root cause.
This is a supporter feature. Create a free account, then try every supporter feature free for 7 days.
What this module covers
You will be able to
- Go from a symptom to the root cause by checking the right things in the right order
The lesson
- Why it matters
- The concept
- Step by step
- In the real world
- Common mistakes
- What to test
In the module
- The lesson, with diagrams, common mistakes and what to test
- A worked example you can change: Troubleshooting a symptom
- Practice: 2 kinds of generated exercise, each with a step-by-step solution
- A quiz of 8 questions
Key terms
- Format error
- Response code 30: the host could not parse the message, often because of a length, bitmap or encoding mismatch.
- Incorrect PIN
- Response code 55. When every PIN fails, suspect the PIN key, PIN block format or PAN field before the cardholder.
- Issuer unavailable
- Response code 91: the issuer or switch did not answer. The acquirer may stand in, decline or retry, depending on the rules.
- KCV mismatch
- Two sides compute different check values for what should be the same key, which means the key was entered, combined or wrapped wrongly.
- Late response
- A response that arrives after the sender timed out and reversed. Response code 68 is used in some networks; the late approval must not be acted on.
- MAC failure
- The receiver's MAC does not match: a wrong MAC key, wrong data range, padding or a field changed after MACing.
- Root cause
- The fault that actually produced the symptom, such as a wrong key, an off-by-one length or a missing reversal.
- Symptom
- What the failure looks like from outside: a response code, a timeout, a rejected message, a wrong total. Troubleshooting works back from it to the cause.
The lesson, worked example, practice and quiz open with a supporter pass, which you can try free for 7 days.