Mask a Resident Registration Number
Before you send out a residence certificate, an ID copy or a contract,
mask the Resident Registration Number first.
Automatic detection checks the number's structure, so it catches spots that are easy to miss.
Name: Alex Hong
RRN: 000000-0000000
* Synthetic example. You can choose to mask only the last part.
When you need this
Sharing only what confirmation actually requires
is the basic rule of protecting personal information.
Submitting a residence certificate
Many recipients never ask for the last seven digits.
Mask what isn't required before you send it.
Sending a copy of an ID card
In an ID photo used for a contract or verification,
mask the second half of the RRN and any license number the recipient doesn't need.
Working on a document with AI
Before pasting text that contains an RRN into an AI,
swap it for a pseudonym token and work without ever exposing the original.
Detection that reviews the shape of an RRN
Flagging every 13-digit run of numbers would also catch order numbers and account numbers as false positives.
Garimi checks whether the first six digits form a valid birth date and whether the seventh digit is a valid gender/century code.
A clean match is selected with confidence; an ambiguous one is shown as a candidate.
The final call is always yours.
How to mask an RRN
Files and text follow the same flow.
- Step 1
Open a file or paste text
Open images and PDFs in File mode;
paste copied text into Text mode. - Step 2
Review what was found
RRN-shaped candidates are found by checking the birth-date, gender and century digits, not just the digit count.
- Step 3
Mask it
In a file, the matching pixels are changed.
In text, it's replaced with a pseudonym token like [RRN_1]. - Step 4
Save or copy
Save the masked file or copy the replaced text.
A saved file's original cannot be recovered.
Frequently asked questions
What is a Resident Registration Number, and how does Garimi find one?
A Resident Registration Number (RRN) is South Korea's national identity number, given to every citizen — comparable in sensitivity to a US Social Security Number. It has 13 digits, formatted 6-7, encoding a birth date followed by a digit for gender and century.
Garimi looks for that 6-7 digit shape and then checks whether the first six digits form a valid date and the seventh digit is a valid gender/century code. It recognizes hyphens or spaces in between, and shows an incomplete or ambiguous match as a candidate for you to judge rather than confirming it automatically.
Can I mask just the last part of the number?
Yes. In a file, you can drag to select exactly the last seven digits and mask only that part.
Is the RRN ever sent to a server?
No. Detecting, masking and saving all happen inside your browser.
The original number is never sent to any server.
Does it also find Foreigner or Business Registration Numbers?
Yes. A Foreigner Registration Number is checked with the same structural review as an RRN,
and a Business Registration Number is checked against its official checksum.
Mask an RRN right now
Open the link and use it right away — no sign-up required.
The number never leaves your browser.