Paste a clear PIN block and this page names the format and the PIN length it declares, then tells you what else can and cannot be read from it. It does not recover PINs, by design.
A PIN never travels as digits. It is packed into a fixed-size block together with padding and, in most formats, combined with the card number — then encrypted. The block format says how that packing was done.
Knowing the format matters when two systems disagree about it, which is the usual cause of a PIN that verifies on one host and fails on the next.
All of them start the same way: the first character is the format number, the second is the PIN length. What differs is the padding and whether the card number is mixed in.
| First character | Format | Block size | Card number | Used for |
|---|---|---|---|---|
0 | Format 0 (ISO-0, also ANSI X9.8) | 8 bytes | Yes | The one you meet most often in online PIN translation |
1 | Format 1 (ISO-1) | 8 bytes | No | Used when no card number is available — a PIN change, for example |
2 | Format 2 (ISO-2) | 8 bytes | No | Offline verification against the chip only; never sent online |
3 | Format 3 (ISO-3) | 8 bytes | Yes | Like format 0, but the padding is random instead of fixed |
4 | Format 4 (ISO-4) | 16 bytes | Yes | The AES-era format, and the one new deployments are built on |
Format 0 is the one most systems exchange. Format 2 is worth singling out because it is defined for offline verification against the chip and is not meant to travel online at all — finding one in a network capture means something is configured wrong rather than that you have found a clever optimisation.
In formats 0 and 3 the block is the PIN field combined, character by character, with a field built from the card number. That field begins with four zero characters — so the first two characters of the PIN field pass through unchanged. That is the whole reason this page can name the format and the length of a format 0 block without knowing anything else.
Everything after those two characters is mixed with the card number, so the digits you see there are not the PIN. Reversing that mixing needs the card number, and doing it would produce the PIN. That is why this page reads two characters and stops.
A PIN block only exists in the clear inside a hardware security module. What travels in DE52 is that block encrypted under a key shared with the next node, and each node decrypts and re-encrypts it under the key for the following hop — PIN translation.
Encryption randomises every character, including the first two. So pasting a DE52 value from a network trace into this page gives a first character that is usually not 0 to 4, and when it happens to be, the format it names is a coincidence. If the value came off the wire, the honest answer is that you cannot tell what is inside it, and neither can anyone else without the key.
This page is useful at the other end of that process: when you are building or debugging the block before it is encrypted, and want to confirm the format and length are what you intended.
Formats 0 through 3 were designed around eight-byte block ciphers. Format 4 is built for AES, so the block is sixteen bytes rather than eight, the padding rules changed, and the card number field is combined with the PIN field using the cipher rather than by simple character-by-character mixing.
The practical consequence during a migration: a system expecting format 0 cannot read a format 4 block, and the failure looks like a wrong PIN rather than like a format mismatch. When PIN verification starts failing across a whole population after a change on either side, the format number is the first character to look at.
It will not recover a PIN. Not from a format 0 block plus a card number, not from a format 1 or 2 block, not at all.
The formats themselves are a public standard and worth explaining, which is what this page is for. A tool that turned a block back into a PIN would be a different thing entirely, and it is not something we are going to publish. If you need to verify a PIN, that belongs inside a hardware security module with the key, which is exactly where the design intends it to happen.