NFCのトピックDecryption of SDMENCFileData is incorrect about NTAG424DNA

Decryption of SDMENCFileData is incorrect about NTAG424DNA

long19890829 — Tue, 07 Jan 2020 16:04:35 GMT

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：

https://my424dna.com/?picc_data=00000000000000000000000000000000&enc=78787878787878787878787878787878&cmac=0000000000000000

Read URL from Tag：

https://my424dna.com/?picc_data=E704C53A168DCD09F9E9A86D93BA3037&enc=570296360EBE9656E25A734840C5439F&cmac=2B006FCEC17EA26A

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
		37383738373837383738373837383738

Tag Setting：

Thanks!

ZhuLong

Re: Decryption of SDMENCFileData is incorrect about NTAG424DNA

Kan_Li — Tue, 14 Jan 2020 06:11:53 GMT

Hi Long,

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

Thanks for your patience!

Have a great day,
Kan

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Re: Decryption of SDMENCFileData is incorrect about NTAG424DNA

long19890829 — Wed, 15 Jan 2020 15:11:04 GMT

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

Re: Decryption of SDMENCFileData is incorrect about NTAG424DNA

vijayhues — Wed, 29 Dec 2021 18:14:31 GMT

Were you able to resolve this issue? I'm running into the same issue and the steps mentioned in the application note & data sheet don't help. The example value provided in the application note works fine though. Any inputs?