SMS encryption and decryption by SIM-Card (USIM)

Question

I Want to write a javacard applet for SIM-Card (USIM) to encrypt and decrypt SMS for specific number. i don't want to install any application on mobile phone and SIM-card applet has to detect the message is belong to specific number and encrypt or decrypt it. Can i write such javacard applet by SIM toolkit package or anything else to do this process technically?

Answer 1

Yes, such application can be written by the help of sim toolkit API's.

Use the following toolkit event for processing your application: -

• ENVELOPE(SMS-PP ... formatted) from 3GPP TS 31.130 V6.6.0 (2007-06)
• From envelope handler, extract the origin address (refer TAG)(phone number of sender).
• Do the operation.

Answer 2

to encrypt and decrypt SMS for specific number.

You would have SIM applet installed on the originator and recipient's SIM and the STK Toolkit menu application needed. Basic DSTK menu application shall be developed to send encrypted SMS. You may need to protect to access this application with PIN code. Let the user the fill text area with any alphanumeric input and next page collect the recipient number. Encrypt text and send it your ESME application as User Data using SEND SHORT MESSAGE proactive command.

In order to send your secure data to ESME application using SMS-PP, it is required to have short code and SMPP connection from ESME application to SMSC. ESME application decomposes the secure data, re-generates it for recipient's SIM applet by setting data coding scheme (0xf6), signs with OTA keys for the recipient number and sends the secure data directly to recipient's SIM.

SIM applet on recipient's SIM processes the secure data, decrypt and shows it as OTA push on recipient's display.