How the number is built and checked
A PPS number is seven digits followed by one or two letters: 1234567T, or 1234567FA for the range issued from 1 January 2013. The first letter is the check character for every number. The second was traditionally a W, for numbers given to married women on their husband's number, and from 2013 another letter extends the range. [1]
The Department of Social Protection describes the check letter as a weighted sum of the digits taken modulus 23, with the second letter counted as A = 1, B = 2 and so on (W or a blank counting 0) and weighted 9. Its own results: 1234567 gets T, and 1234567 with A in ninth place gets F, giving 1234567FA. [1]
The Department does not print the weight of each digit. nullcipher uses 8 7 6 5 4 3 2 from the left and looks the remainder up in W, A, B … V, which reproduces both of its results: 1×8 + 2×7 + 3×6 + 4×5 + 5×4 + 6×3 + 7×2 = 112, and 112 mod 23 = 20, the 20th letter T; 112 + 9×1 = 121, and 121 mod 23 = 6, F.
A check letter is right by chance about one time in 23, and seven digits and a letter are a common shape for reference codes. So nullcipher masks it only when PPS, PPSN, PPS number or personal public service number stands within 40 characters before it. Upper and lower case both count.
How nullcipher recognises it
Seven digits, a check letter and, for numbers issued from 2013 (and the old “W” numbers), a second letter: 1234567T, 1234567FA. The check letter is the digits times 8 7 6 5 4 3 2 plus 9 times the second letter (A = 1, B = 2 … ; W or none = 0), summed, mod 23, looked up in W A B C … V. Upper or lower case. Masked with a context word — PPS, PPSN, PPS number, personal public service number — within 40 characters before it.
This is the rule text of the “Irish PPS number” detector in the masking engine, copied from the engine when this page was built. Detectors run in a fixed order and, where two overlap, the earlier one wins.
Example (fake)
PPSN 1234567FAnullcipher replaces it with [PPSN_1]. This is the Department of Social Protection's own example of a new-range number (check letter F, second letter A).
Why it matters in an AI chat
Only bodies named in legislation, and their agents, may use the PPS number — the Department keeps a register of who they are and what they use it for. A document that carries it is usually an official one: tax, welfare, health or employment.
It has been the target of phone and text scams in which callers claim to be from the Department and say the person's PPS number has been “compromised”, then ask them to confirm their name, PPS number and bank details. Gardaí say neither they nor the Department ever ask for these in a cold call or text.
Masked, the AI sees [PPSN_1] and can still help with the rest of the text.
If it already leaked
- If someone contacts you about it by phone or text, do not engage or call back, and never give personal data to people who contact you that way. [3]
- If you think you have been targeted, contact your bank and the Department of Social Protection, note the number that contacted you, and report it at your local Garda station. [3]
- If it only went into an AI chat and there is no sign of misuse, delete the conversation — how, for each major assistant, is on the page listing every type. The PPS number itself stays the same.
Sources
- Extension of the Personal Public Service Number Range — Department of Social Protection (welfare.ie) — checked 2026-10-03. The page is no longer online; read in the Internet Archive's copy of 25 December 2019: archived copy.
- Who can use my Personal Public Service (PPS) Number — gov.ie — checked 2026-10-03.
- Gardaí and Department of Social Protection advise public of fraudulent phone calls and texts requesting personal data (April 2021) — An Garda Síochána — checked 2026-10-03.
Open the full masking tool to mask a whole log, .env file or e-mail — every type at once — and restore the values in the AI's answer. Or see all 242 detectors, with a page for 59 secret types, and how to delete a chat you already sent.