Proxmark3 community

mjchen

Member

Registered: 2015-07-18

Posts: 3

How to write read only blocks

Hi,

I'm a total noob at this.
I'm using mifare classic tool to write my card but there are several blocks I can't access because they are read only.

is there any ways to still write to those blocks?

thank you guys in advance

piwi

Contributor

Registered: 2013-06-04

Posts: 704

Re: How to write read only blocks

It depends on what you mean with read-only.

1. You only know the key to read the block, but you don't know the key to write the block: try one of the functions to recover the correct key.

2. The access conditions for the respective block don't allow writing for both Key A and Key B: see if you can change the access condition by writing to the sector trailer.

3. the acccess conditions for the sector trailer don't allow writing to it neither with Key A nor with Key B: give up.

4. you are talking about block 0: if it isn't a magic Chinese card: give up.

mjchen

Member

Registered: 2015-07-18

Posts: 3

Re: How to write read only blocks

OK so I know that the access bit is locked (keyA and B are only writable and ACbits are only readable)
and my value block bits are 001, which means it can only decrease right?

But just out of curiosity, how is the company able to recharge cards then?

mjchen

Member

Registered: 2015-07-18

Posts: 3

Re: How to write read only blocks

please excuse my inaccuracy in stating the terms

Stanger

Contributor

Registered: 2015-07-22

Posts: 21

Re: How to write read only blocks

You first have to make sure that the value block's do represent the value on the card and not just some random counter. It is possible to write a value block without you having permission for it. It is difficult way and I doubt if it's implemented in commercial systems.