Key takeaways
- Phone numbers are turned into SHA-256 hashes on your device before they are compared.
- The C Chat server does not store the hashes used for matching.
- Matching is optional: you can also reach people by @username or through your team.
- Matched contacts can be messaged directly, with no message requests to accept.
- Block and report are available if someone you match with is not welcome.
Most teams already have their coworkers saved in their phones. The fastest way to get a new messenger working is to let people see which of those contacts are already there. The risk is obvious: a careless app can copy every name and number from every employee’s phone onto its servers. C Chat was built to give you the convenience without that copy.
What contact matching does in C Chat
Contact matching shows you which people in your phone’s address book already have a C Chat account, so you can open a direct conversation with them in one tap. It is meant for the moment right after sign-up, when you want to message your supervisor, a colleague on another site or a contractor you work with every week.
Here is what happens under the hood, in plain terms:
- Your device reads the phone numbers in your contacts.
- Each number is converted into a SHA-256 hash, a fixed-length fingerprint that cannot simply be read back as the original number.
- Only those hashes are compared with the hashes of registered C Chat accounts.
- The server returns the matches and does not store the hashes you sent.
Names, notes and other fields in your address book are not part of the comparison. For the technical background, read how contact matching protects phone numbers.
How to use contact matching step by step
- Sign up with your phone number. C Chat sends a code by SMS; once you enter it, your account is tied to that number.
- Allow contact access when asked. Your phone’s system prompt controls this; you can decline and still use C Chat.
- Review the matches. You see the contacts who already use C Chat.
- Start a conversation. Tap a person to open a direct message. There is no request to accept, so the message arrives immediately.
If someone is not in your contacts, use their @username instead, or find them inside a team you both belong to.
Real scenarios from business teams
- A cleaning supervisor joins C Chat and sees right away which of her crew leads have already signed up, then messages the two who have not yet joined the client group.
- A new hire at a logistics company finds the dispatcher and two drivers he already had saved, without asking anyone for their numbers again.
- A team leaving personal WhatsApp groups uses matching so that everyone reconnects in minutes. See how to move work off personal WhatsApp groups, and how C Chat compares in C Chat vs WhatsApp for business teams.
Privacy, permissions and limits
Contact matching works with your permission, and you can say no. Declining does not limit messaging: teams, invitations and @usernames all work without it.
A few honest limits are worth knowing:
- Hashing is not magic. Phone numbers have a predictable structure, so a hash on its own is not full anonymity. Not storing the hashes is what reduces the exposure.
- Matching shows presence. If a coworker has your number and uses matching, they can see you are on C Chat. If that matters, share your @username rather than your number.
- Matched people can message you. Direct messages need no request. If a match is unwelcome, use block and report.
Direct messages you start from a match are private between the two people. They are not part of the group audit that team owners and admins can run; see private one-to-one conversations at work.
Tips for admins
- Tell staff what matching does before rollout. One sentence helps: “C Chat compares fingerprints of numbers on your phone; it does not keep your contacts.”
- Do not rely on matching for onboarding. Invite people to the team by link, QR, WhatsApp, SMS or email so nobody is missed.
- Cover it in your BYOD rules. Use the guide on writing a BYOD policy for work messaging and the overview of work messaging on personal phones.
- Review the wider picture. Contact handling is one piece of business messaging security; the full privacy policy covers the rest.
Getting started
Open the web app at getcchat.com/c, sign up with your phone number or email, and create or join your team. Contact matching is there when you want it, and your team works fine without it.
Frequently asked questions
Does C Chat upload my phone contacts?
C Chat does not send your address book in readable form. Each phone number is hashed with SHA-256 on your device, only the hashes are used for matching, and the server does not store them after the comparison.
Is a hashed phone number completely anonymous?
Hashing hides the number from casual view, but phone numbers follow known formats, so hashing alone is not the same as anonymity. That is why C Chat also avoids storing the hashes on the server, which limits what could ever be exposed.
Can I use C Chat without sharing contacts at all?
Yes. Contact matching is one of three ways to find people. You can also start a chat by @username or message the members of a team you belong to, without giving C Chat access to your contacts.
Will people in my contacts know I joined C Chat?
People who have your number saved and use contact matching can see that you are on C Chat, the same way most phone-based messengers work. If you prefer to be reached by handle, share your @username instead of your number.