One-time passcode (OTP): A short, randomly generated code that is valid for one sign-in or action only and expires after a brief time window, used to prove control of a phone, email inbox or authenticator app.
Also known as: OTP, One-time password, Verification code
Key takeaways
- An OTP works once and expires quickly, so it can't be reused like a password.
- OTPs arrive by SMS or email, or are generated by an authenticator app.
- App-generated codes resist interception better than SMS codes.
- C Chat signs you in with a one-time code sent by SMS to your phone or by email.
- Never share an OTP: anyone who asks you to read it out is almost certainly an attacker.
You probably type several one-time passcodes a week: to log in, approve a payment or confirm a new device. They feel simple, but the details of how they are generated and delivered decide how much protection they really give.
One-time passcode (OTP): a plain definition
An OTP is a code that works exactly once. After it is used, or after a short timer runs out, the service rejects it. That single property makes OTPs much harder to abuse than passwords, which stay valid for months and are often reused across sites.
How it works
There are two main ways a service creates OTPs:
- Sent codes. The server generates a random code, stores it briefly, and sends it to you by SMS or email. You type it back, the server compares, and the code is discarded.
- Generated codes (TOTP). An authenticator app and the server share a secret set up once, usually by scanning a QR code. Both compute the same 6-digit code from that secret and the current time, so nothing travels over SMS.
| Delivery | Strengths | Weaknesses |
|---|---|---|
| SMS | Works on any phone, no app needed | Can be redirected via SIM swap or intercepted |
| Works without a phone number | Only as secure as the inbox | |
| Authenticator app | Not sent over the network | Needs setup and a recovery plan |
Why it matters for business messaging
For a team chat, the OTP is often the front door. If an attacker gets the code, they get the account, and with it the ability to read groups and message colleagues under a trusted name. That is why attackers focus on tricking people into sharing codes, a classic social engineering move, or on redirecting SMS through a SIM swap.
How it relates to C Chat
C Chat uses OTPs for passwordless authentication. You sign up with your phone number and receive a code by SMS, or with your email and receive a code by email, similar to WhatsApp. There is no password at all, which removes the risk of reused or leaked passwords. See the passwordless sign-up page for the full flow.
Because the code is the key, a few habits make a big difference:
- Treat every sign-in code as private. Do not forward it, read it aloud or paste it into a chat.
- Secure what receives the code. Add a carrier PIN to your phone line and enable two-factor authentication on your email.
- Report unexpected codes. An unrequested code means someone tried to log in; tell your team admin.
- Remove people who leave. Team owners and admins can take former staff out of the team so they lose access to its groups.
For an honest look at the trade-offs of code-based login, read is passwordless login secure?
Related terms and common misconceptions
- “An OTP and a PIN are the same.” A PIN is fixed and reused; an OTP changes every time.
- “OTPs stop phishing.” Not fully. A fake login page can capture a code and use it instantly. Learn the warning signs in how to spot phishing in chat apps.
- “OTPs replace SSO.” They solve different problems; single sign-on centralizes many logins under one identity.
Getting started
Try code-based sign-in yourself: open getcchat.com/c, enter your phone number or email, and type the code you receive. You can create a team and invite colleagues in a few minutes, and read more about protection on the security page.
Frequently asked questions
How long is a one-time passcode valid?
It depends on the service. Authenticator app codes typically rotate every 30 seconds, while codes sent by SMS or email usually expire within a few minutes. A code is also invalidated as soon as it has been used.
Is an OTP the same as two-factor authentication?
Not exactly. An OTP is a tool; two-factor authentication is a method. An OTP is often the second factor after a password, but it can also be the only factor, as in passwordless sign-in, where the code proves you control a phone or inbox.
Why do scammers ask for my verification code?
Because the code is the key to your account at that moment. A common scam is to trigger a login to your account and then message you pretending to be a friend, colleague or support agent asking you to forward the code. No legitimate service needs you to share it.
I did not request a code but received one. What should I do?
Do not share it or enter it anywhere. Someone may be trying to log in with your phone number or email. Make sure your email account is secured and consider asking your mobile carrier for a SIM lock or port-out PIN.