How can I protect access to an SD card, so that only authorized users can read or modify the content of the SD card. Currently everybody who has physical access to the SD card can read or modify everything.

  • What are you using the SD card for? Is it possible to give everyone their own card? – this.josh Oct 25 '11 at 7:11
  • The SD card is used to store the configuration of an embedded system. Now everybody who has physicak access to the SD- card can change the configuration of the embedded system. To avoid this situation I need a protection, that allows only authorized users (e.g who knows the password ) to read and modify the configuration. – user536 Oct 25 '11 at 10:53
  • How are changes made to the SD card, are they made by the embedded system or from a normal computer? Is the card required to use the emebedded system or just to load configuration? – this.josh Oct 25 '11 at 22:18
  • Changes can be made online/(over a TCP/IP Network) or using a PC. Both options must be supported. The access over the network is protected using IPsec but the physical access is not protected at all. – user536 Oct 26 '11 at 6:31

Simplest solution for protecting against unauthorised viewing or modification: encryption. You can use TrueCrypt, PGP, GPG, OpenPGP etc to either encrypt individual files on the card or to set up an encrypted volume for the whole card.

This will mean only those people who have the passphrase will be able to access the data (given the usual assumptions around correct implementation, no sharing of keys etc)

The latter solution also allows you to effectively securely delete the card, by getting rid of the encryption passphrase (or password or certificate etc)

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    Of course, now you have to manage access to the encryption key which may or may not be easier. – Steve Oct 24 '11 at 16:04

Secure digital cards define a protocol and commands for password protection of read/write access to the part of the stored data. Data access is impossible without presenting a password.

A specification snapshot is available at http://blog.ednchina.com/Upload/Blog/2007/10/26/eb26e3c5-586e-43c7-a0a1-ff4920ee7113.pdf

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