NXP Semiconductors
AN10927
MIFARE and handling of UIDs
1. Introduction
This document shows the use of UIDs in contactless smartcard systems. It indicates
recommendations about the use of Random ID, the mixed use of 4 byte (single size) and
7 byte (double size) UIDs in the same system, and it describes the options how to
upgrade 4 byte UID systems to use 7 byte UID smart cards.
Note:
A UID is not a “serial number”, but a unique identifier. There is no recommendation
how to turn the array of bytes into an integer.
Note:
“UID” is a common expression, defined in the ISO/IEC 14443-3. In some case the
UID is even not unique (like RID or NUID, see below).
Note:
The 4 byte UID is called “Single Size UID”, too. The 7 byte UID is called “Double
Size UID”, too. The 10 byte UID is called “Triple Size UID”, too.
2. MIFARE and ISO/IEC 14443 UIDs
In this section the use of UIDs according to the ISO/IEC 14443 is described. Fig 1 shows
the three different UID sizes defined in ISO/IEC 14443-3 as they are used during the
anti-collision and selection procedure.
UID0 UID1 UID2 UID3
UID0 UID1 UID2 UID3CT UID4 UID5 UID6
UID3 UID4 UID5
UID6
CT
UID7 UID8 UID9
4 byte UID
7 byte UID
10 byte UID
Cascade Level 1 Cascade Level 2
Cascade Level 3
BCC
BCCBCC
UID0 UID1 UID2CT BCC BCC BCC
(1) BCC = Block Check Character, it is calculated as exclusive-or over the 4 previous bytes.
(2) CT = Cascade Tag, to indicate a following cascade level.
Fig 1. UIDs according to ISO/IEC 14443
Fig 2 shows the Anticollision sequence, which is a mandatory part of the card activation
sequence. It automatically selects a single PICC with 4 byte UID (= Single Size UID), 7
byte UID (= Double Size UID) or 10 byte UID (= Triple Size UID).
Cascade Level 1
In the Cascade Level 1 the PCD sends the Anticollision command CL1 (0x93) and the
PICC returns
• either the 4 byte UID (UID0...UID4) and one byte BCC,
• or a Cascade Tag (CT) followed by the first 3 byte of the UID (UID0...UID2) and one
byte BCC.
The CT (0x88) indicates that the UID is not yet complete, and another Cascade Level
has to follow.
AN10927 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2010. All rights reserved.
Application note
PUBLIC
Rev. 2.0 — 01 September 2010
190720
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