#### Original Writeup - [https://github.com/CTSecUK/Syskron-Security-CTF-2020/blob/main/Write-ups/Check%20Digit.md](https://github.com/CTSecUK/Syskron-Security-CTF-2020/blob/main/Write-ups/Check%20Digit.md) -----# Check Digit
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## Details
![Details](https://github.com/CTSecUK/Syskron-Security-CTF-2020/raw/main/Write-ups/images/check_digit_details.png)
First i started with a google search with some of the text from the description and added ISO Standards on the end. "IMEI numbers, credit card numbers and UIC wagon numbers ISO Standards" 
![Image](https://github.com/CTSecUK/Syskron-Security-CTF-2020/raw/main/Write-ups/images/check_digit_google.png)
I click on the first link which happens to be a Wikipedia page for payment Card Numbers. At that point i though i was onto something here...
![Image](https://github.com/CTSecUK/Syskron-Security-CTF-2020/raw/main/Write-ups/images/check_digit_wikipedia.png)
Looking at the page there is a ISO standard in the main section.
![Image](https://github.com/CTSecUK/Syskron-Security-CTF-2020/raw/main/Write-ups/images/check_digit_iso_standard.png)
I tried that ISO standard as that seems legit.
Here is the Flag   ***syskronCTF{ISO/IEC-7812}***