Is the UID on mifare classic read only?

Question

Are UID read only on mifare Classic cards? (I mean in normal cards, not UID changeable mifare cards)

I thought it was not possible but this document states that it can be changed http://arxiv.org/pdf/0803.2285.pdf :

Consequences of our attack Any system using mifare Classic cards that relies on the secrecy or the authenticity of the information stored on sector zero is now insecure. Our attack recovers, in a few minutes, all secret information in that sector. It also allows us to modify any information stored there

Is that true?

Answer 1

UID is readable only on all MIFARE cards according the official FAQ.

Can I assign my own UID to MIFARE Cards?

UIDs for MIFARE cards are assigned during the production and it can never be changed thereafter.

Answer 2

It depends on the card manufacturer. Because with Classic Mifare cards with read-only UID came also so called "magic" cards which have rewritable block 0 where is also stored card UID. To write block 0 you have to usually send "backdoor" sequence to the card, which opens block 0 for writing.

Here are examples of such cards: http://www.proxmark.org/forum/viewtopic.php?id=6545