NFC encryption issue

[RamaKrishna]

Hi I'm trying to write some data in to ST25dv64 NFC TAG using custom mobile application, before writing data into NFC tag we are encrypting message. encryption method is AES 128 CBC, the encrypted message has some non-printable characters, like 0x91, 0x8a, 0xdf which are getting converted in to 0xEF 0xBF 0xBD when stored in NFC EEPROM, when we read NFC tag using host controller, we are seeing in the memory in the place of one byte (say 0x91) we are seeing 3 bytes (0xEF 0xBF 0xBD), because of this decryption is failing on host controller. 

I'm new to this AES encryption and I'm not sure where the issue is? whether it is in NFC TAG or encoding data. 

Any help would be appreciated. Thanks in advance.

[Brian TIDAL · Accepted solution]

Hi,

data are written inside the tag memory thanks to one of the ISO 15693 WRITE commands (Write Single Block, Extended Write Single Block, Write Multiple Blocks or Extended Write Multiple Blocks). Those commands contain binary values of the data to be written. Those binary values are written inside the EEPROM without any modification. 

Therefore, the tag memory contains the data that the application has sent. If the written data are not the expected ones, this means the application has sent wrong data.

Rgds

BT

[RamaKrishna]

Hi,

Thank you so much for the confirming, I will check for what is going on app side.