CTFtime.org

Check digit

by M1st3r3 / CTSecUK

Tags: standard 

Rating:

#### 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)

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# 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}***

Original writeup (https://github.com/CTSecUK).

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