Saturday, November 04, 2006

Deleted SMS text messages

Deleted SMS text messages

GSM 11.11 (ETSI TS 100 977) is a Standard containing mandatory and optional requirements relevant to Subscriber Identity Module (SIM) cards. An optional service that an Operator may provide to a subscriber of its services is Short Message Service (SMS) text messaging. The requirements relating to storing sent and received SMS text messages, in the user memory area of the SIM card, are identified at GSM 11.11 cl10.5.3. When a message that is received and is subsequently deleted by the user of the SIM, the user can no longer gain access to that data. The details about a particular SMS message that has been deleted are removed from the SIM's memory table thus the mobile telephone will no longer display the SIM details of that message to the user.

Although the details of the SMS text message are no longer accessible by the user, GSM 11.11 makes it clear the physical data relating to the entire text message may still be recorded on the card. GSM 11.11 procedure for "Erasure" of text messages states:

GSM 11.11 cl 11.5.2
"Erasure: The ME will select in the SIM the message area to be erased. Depending on the MMI, the message may be read before the area is marked as "free". After performing the updating procedure with EFSMS, the memory allocated to this short message in the SIM is made available for a new incoming message. The memory of the SIM may still contain the old message until a new message is stored in this area."

Using specialist examination tools it is therefore possible to recover erased (deleted) SMS text messages from a SIM card. Where a previously deleted message has been over-written by either new data allocated to the memory area previously occupied by the deleted data or the handset automatically over-writes as a function of its operating procedure (usually over-writes with 000000's) the erased (deleted) data in the SIM are no longer recoverable. Hopefully this
information will assist if you are asked is it possible can deleted text messages be recovered, and, if not recoverable, why not?

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