(Reprinted from https://defcongroups.org)

As the DEF CON Groups Signaler (handling group communications), I wrote this to help all new DEF CON Groups community leaders in determining what their group name will be.


How To Determine What Your New DEF CON Group’s DCXXXX Number Will Be

by @aprilwright

One of the most frequently asked questions and points of confusion for new DCGs is in regards to naming of their group.

Groups do not get to choose their own number – you can’t be DC666 or DC000 or anything like that just because you like it. There is actually a system we adhere to 🙂

We HIGHLY RECOMMEND that you do not: buy domain names, register social media handles, or create branding _until_ your group is listed on the defcongroups.org website.
Yes, “after being listed on the website”. That means continuing to wait to do these things even after receiving the email from us stating that a request has been made to add your group to the website.  The “request to be added” email is NOT final confirmation of establishment of your group. Only being added to the website is confirmation.
This post is intended to help new group leaders avoid spending time, effort, and/or money on branding that may need to be changed later, and to explain how the number scheme works and why it exists.

As new groups form, we must evaluate the numbering / naming convention of the group for accuracy and fit within the numbering and naming system rules.
It is not fun for us to have to tell a new group leader (who has already registered a Twitter account, bought a domain name, and designed a logo) that the name they assumed they would have e.g. DC111 is really going to be DC112345!  It unfortunately happens all the time, and can cause disappointment, so we want to prevent that.
We do not want you to go through any unnecessary work or spend any money on domain names only to have to change them!
In addition, sometimes the Signaler who answers the dcgroups@ emails will submit a ticket asking to have your group added to the site, they will send you a notification saying it has been submitted, but then a secondary check by the rest of the team will determine that the DC#### name actually needs to be changed.
It is therefore advisable to wait until your group is *officially listed on the site* before doing anything that may cost money or confuse your community.
We can easily make changes to your listing after you’re officially an organized DEF CON Group, but you cannot get your money back from a domain name you purchased that is no longer appropriate!!!


Many groups want to choose their own name. We get lots of requests for DC0101010101 or DC42…

The reality is that group names are based on telephone dialing codes, as dialed from the USA. This is to make sure group names are unique. If we were to have two groups named DC1234, and one was in the USA and the other one is in Antarctica, that would be very confusing!

“The International Telecommunication Union (ITU) has established a comprehensive numbering plan, designated E.164, for uniform interoperability of the networks of its member state or regional administrations. It is an open numbering plan, however, imposing a maximum length of 15 digits to telephone numbers. The standard defines a country calling code (country code) for each state or region which is prefixed to each national numbering plan telephone number for international destination routing. You can read more about this here:  https://en.wikipedia.org/wiki/Telephone_numbering_plan

The general rules for dialing internationally from the USA, which we follow, are:

– For calls to most countries: 011 + country code + phone number
– For calls to countries within the North American Numbering Plan: 1 + area code + 7 digit local number, same as dialing a US state to state call

In its simplest form, this works as such:
If I dial 1-312-555-5555 to reach Chicago Illinois USA, the Chicago DC # would be DC312.

North America uses non-overlapping area codes, which makes things simple for groups in North America.  If I were to dial Edmonton, Canada from the US, I would dial 1-780-555-5555.  “780” does not exist as an area code within the US because of ITU.  Since there is no “780” area code within the USA, 780 is unique and there is no overlap. Edmonton would be DC780. There is no other DC780 other than Edmonton.

The confusion with naming really starts with international groups outside North America. This is because of the use of International dialing codes (11 from USA) + Country Codes + City Codes/Area Codes being required in addition telephone number

Let’s look at an example of International Numbering:
816 is an area code used to dial Missouri, USA.
“81” is also the international code to dial Japan and 6 is the local area or city code to dial Osaka (i.e. 816).
Therefore, by preceding Osaka’s 816 dialing code with the international dialing prefix 11, we get DC11816.  This makes it clear that DC11816 is the Osaka group, and DC816 is the Missouri group.

You can search here to help you, but remember that final naming is determined by the DEF CON Groups team.
1) Visit https://countrycode.org
2) Choose “United States” as the source
3) Enter your country
4) Scroll down to find your city (if applicable)
5) Concatenate the numbers to figure out your dialing code
For a variety of reasons, a second group within a city/country may be desired by local hackers.
If you want to start a group in Shanghai, and there is another group in Beijing, or if you want to start a group in Brugges (113250) and there is already a group in Brussels (11322), you do not have a problem. They are geographically diverse, and have different dialing codes.
However, some cities and countries only have one dialing code, e.g. Luxembourg is 11352. If a second Luxembourg group were created, the first / original group that was formed would remain DC11352, and the secondary group would be DC11352-A, any third group would be called DC11352-B, et al.  Sure, three DEF CON groups in Luxembourg may seem silly, but it’s just an example 🙂
Sometimes a group already exists within a single city, for example, Chicago DC312. Chicago is a large city, and there are also student groups on-campus vs public groups.
In this case, if there is a secondary area code, that can be used. For example, Chicago has an area code of 312 and another area code of 773.  Group leaders can apply as DC773 when there is already a DC312, or they can choose to be DC312-A, as the dialing codes overlap.

We admire your go-getter attitude in that you want to have the website and social media accounts ready to go when you apply to be a group, but doing so is not always in your best interest.
If you are an international group, we recommend waiting to register or purchase anything with the name of your group until your group name is confirmed by us.
Remember: You can send us an update request at any time to keep your info current, add social media, links, etc. We love to hear about what you’re working on and keeping the site updated with fresh content from the groups.
Please DO NOT HESITATE to contact us with any questions – we are here to help!!!