Decryption of SDMENCFileData is incorrect about NTAG424DNA

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Decryption of SDMENCFileData is incorrect about NTAG424DNA

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Contributor II
Hi,
   I have a trouble in decryption of SDMENCFileData, I could get the same data with the Table 4 of 4.4.3.2 Decryption of SDMENCFileData of AN12196, while when I write the demo url = https://my424dna.com/?picc_data=00000000000000000000000000000000&enc=7878787878787878787878787878787... into the tag,enable the mirror feature, and read the tag,I got the new url = https://my424dna.com/?picc_data=E704C53A168DCD09F9E9A86D93BA3037&enc=570296360EBE9656E25A734840C5439.... After the same decryption process, and I get the decryption SDMENCFileData = 37383738373837383738373837383738, which is not equal raw enc=78787878787878787878787878787878, and is the ASCII format. Even I transform the data "37383738373837383738373837383738" into ASCII format "7878787878787878", it only 8 byte length and only the half of the raw enc. Below is my computational process and tag setting, could you help me work out the problem.

Original Demo URL:

Read URL from Tag:

My computational process:

Step

Command

Data Message

1

SDMENCFileData

570296360EBE9656E25A734840C5439F

2

SDMMetaReadKey

’00000000000000000000000000000000

3

SDMFileReadKey

‘00000000000000000000000000000000

4

PICCData

E704C53A168DCD09F9E9A86D93BA3037

5

decrypt UID and counter

UID=0454a292766380 counter=010000

Session Key generation

6

SV1 =C33C 0001 0080 [UID] [SDMReadCtr] [ZeroPadding]

c33c000100800454a292766380010000

7

KSesSDMFileReadENC

cb7b614e2c69e0663bea3135d9dcbe0e

8

IVe = E(KSesSDMFileReadENC; SDMReadCtr || ZeroPadding)

1bdbda6eacb46add1c8a5dae7d526434

9

D(KSesSDMFileReadENC, IVe, SDMENCFileData)

37383738373837383738373837383738

Tag Setting:

tag_setting01.jpg

Thanks!

ZhuLong

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2 Replies

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NXP TechSupport
NXP TechSupport

Hi Long,

How did you write to the tag for the Mirroring features? I may try to reproduce this issue here.

pastedImage_1.png

Thanks for your patience!

Have a great day,
Kan


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Contributor II

Hi Kan,

  Thanks for your reply, please refer to the attachment for tag writting log, and my concern is that why the plaintext(after decryption) of SDMENCFileData is ASCII format, and only the half of the raw data.  

  Thanks!

  Long

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