CODEWITHSUNDEEP
smartcardjavacard
Ryan Russell
Ryan Russell

Reputation: 510

Is it possible to query a GlobalPlatform smart card for its remaining persistent memory?

I have a JavaCard and can call JCSystem.getAvailableMemory(MEMORY_TYPE_PERSISTENT) and return that from my applet, but I want an exact value if its over 32767 bytes.

Upvotes: 1

Views: 1307

Answers (2)

David
David

Reputation: 4047

Javacard with GP 2.2 + ETSI support

If your card supports Global Platform 2.2 and ETSI, you can use GET DATA command.

GP card spec 2.2 section 11.3 states that

Tag ‘FF21’: Extended Card Resources Information available for Card Content Management, as defined in ETSI TS 102 226.

And in ETSI 102.226 section 8.2.1.7.2:

After the successful execution of the command, the GET DATA response data field shall be coded as defined in GlobalPlatform [4]. The value of the TLV coded data object referred to in reference control parameters P1 and P2 of the command message is:

Length Description                            Value
  1    Number of installed application tag    '81'
  1    Number of installed application length  X
  X    Number of installed application
  1    Free non volatile memory tag           '82'
  1    Free non volatile memory length         Y
  Y    Free non volatile memory
  1    Free volatile memory tag               '83'
  1    Free volatile memory length             Z
  Z    Free volatile memory

The response of this command is not restricted to short value because it is using TLV format, which means you can check free memory that is more than 32767 bytes

Upvotes: 3

groissi
groissi

Reputation: 21

In general there is no possibility to get the exact amount of free memory from the card using the standard Java Card API. Because most Java Cards don't even have integer support, the maximum value you can get from the APIs method is 32767 (upper bound of signed short).

If you're lucky, there might be some proprietary API method from the card/OS manufacturer. I've seen some proprietary APIs from NXP JCOP cards but none of them is capable of getting the amount of free memory if it exceeds the upper bound of a signed short.

Upvotes: 1

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