PIN Data
What it is
The encrypted PIN block (8 bytes), produced under the terminal PIN key — ISO 9564 formats 0, 1 or 3. The 16-byte AES format 4 does not fit the 1987 b 64 field.
The PIN never travels in clear: the PIN pad forms an ISO 9564 PIN block (format 0 XORs the PIN field with the PAN; format 4 is the AES-based 16-byte block) and encrypts it under the zone PIN key — commonly a DUKPT-derived key. Each hop of the network translates the block from one zone key to the next inside an HSM; the issuer (or its HSM) finally verifies it against PVV or IBM 3624 offset.
DE 52 on the wire
Bitmap position
DE 52 is bit 52 of the primary bitmap: byte 7, mask 0x10. A primary bitmap with only DE 52 present reads 0000000000001000 in hex.
Length
DE 52 is fixed length: always 8 bytes, with no length prefix. A parser reads exactly that many and moves on.
Size in the message
Exactly 8 bytes of binary data. Interfaces that carry binary data as text send each byte as two hex characters, so the value takes 16 characters there.
Format b
Format b means binary: raw bytes, often shown or sent as hexadecimal text.
Specification reference
Defined in ISO 8583:1987 (base). Card networks publish their own dialect tables (Visa BASE I / V.I.P., Mastercard CIS) that refine formats, lengths, and — for private-use elements — the entire layout. Always confirm against the interface specification you implement.