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Decryption of SDMENCFileData is incorrect about NTAG424DNA

Question asked by long zhu on Jan 7, 2020
Latest reply on Jan 15, 2020 by long zhu
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=78787878787878787878787878787878&cmac=0000000000000000 into the tag,enable the mirror feature, and read the tag,I got the new url = https://my424dna.com/?picc_data=E704C53A168DCD09F9E9A86D93BA3037&enc=570296360EBE9656E25A734840C5439F&cmac=2B006FCEC17EA26A. 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:

 

 

Thanks!

ZhuLong

 

 

 

 

 

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