BQ40Z80EVM-020: ECC authentication

Coman Y

Prodigy 120 points

Part Number: BQ40Z80EVM-020
Other Parts Discussed in Thread: BQ40Z80, BQKEYPACKAGER, BQSTUDIO

Hi,

I want to use ECC authentication. I have some questions as following.

1.What is the meaning of key F key C in the tool bqkey packer?

2.Are the keys all random?

3.After sending the change to bq40z80, how can the R,S value read be confirmed to be correct?

4.Is there any reference code or details of ECC certification?

over 3 years ago

0 Wyatt Keller over 3 years ago

TI__Guru** 102455 points

Hello Coman,

There's a help menu in the program you can use to explain the different features of bqKey Packager.

You program the keys yourself, so they can be set to whatever you need.

You can use online tools to check the values.

We don't have any reference code for the ECC authentication.

Sincerely,

Wyatt Keller

0 Coman Y over 3 years ago in reply to Wyatt Keller

Prodigy 120 points

Hello Wyatt,

Thank you very much for your reply.

If I use a MCU to connect to bq40z80 and send a random challenge to bq40z80, bq40z80 returns the RS value. At this time, I can't use the online tool. How can I make sure that this value is correct?

Sincerely,

Coman

0 Wyatt Keller over 3 years ago in reply to Coman Y

TI__Guru** 102455 points

Hello Coman,

You will need to validate your MCU program before using it in production, using one of the tools can help validate your code.

Sincerely,

Wyatt Keller

0 Coman Y over 3 years ago in reply to Wyatt Keller

Prodigy 120 points

Hello Wyatt,

Thank you very much for your reply.

I can use the online tool to help validate my code, but the problem is I don't know how to write my code. According to ECC authentication method, there is a calculation method to verify whether the values of R and S are correct. But I don't know how to do it, could you help me?

Sincerely,

Coman

0 Wyatt Keller over 3 years ago in reply to Coman Y

TI__Guru** 102455 points

Hello Coman,

We do not have any ECC code examples to my knowledge, you will have to develop it yourself as it is a standard authentication method.

The only documentation we have is in the help menu for bqKeypackager and this app note: www.ti.com/.../sluubu3.pdf

Sincerely,

Wyatt Keller

0 Coman Y over 3 years ago in reply to Wyatt Keller

Prodigy 120 points

Hello Wyatt,

Thank you very much for your reply.

There are many kinds of ECC authentication. Could you tell me more imformation.

For example,

(1) The prime number P, which defines the size of a finite field

(2) Coefficients a and B of elliptic curve

(3) Base point G (generator of subgroup)

Sincerely,

Coman

0 Wyatt Keller over 3 years ago in reply to Coman Y

TI__Guru** 102455 points

Hello Coman,

I can only direct you to the documentation we have posted currently. I need to check the specifics with our FW team. Most customers use SHA authentication.

Sincerely,

Wyatt Keller

0 Coman Y over 3 years ago in reply to Wyatt Keller

Prodigy 120 points

Hello Wyatt,

When I use SHA1 authentication, the key F in bqkey packager is filled with 0xfedcba9876543210fedcba987654321011111111, and the key C is filled with 0xfedcba9876543210fedcba9876543210aaaaaaaa. Then, what is the actual SHA1 128bit key value?Whether I use 0xfedcba9876543210fedcba9876543210, or 0x76543210fedcba9876543210111111, or 0x76543210fedcba9876543210aaaaaaaa, I can't verify it in the tool studio. What's the meaning of Key F and Key C.

Sincerely,

Coman

0 Wyatt Keller over 3 years ago in reply to Coman Y

TI__Guru** 102455 points

Hello Coman,

For SHA authentication the response for a challenge will always be the same, for ECC it can be different. You should be able to verify the key using online tools or bqStudio with bqKeyPackager.

I am reviewing the ECC information.

Sincerely,

Wyatt Keller

0 Coman Y over 3 years ago in reply to Wyatt Keller

Prodigy 120 points

Hello Wyatt,

I summarized my question in the word document, please help to answer it.We look forward to your reply.

bz40z80_question.docx

Sincerely,

Coman

0 Wyatt Keller over 3 years ago in reply to Coman Y

TI__Guru** 102455 points

Hello Coman,

You can check the forum for some answers: e2e.ti.com/.../2953159

You are most likely not matching the expected input for the bqKeyPackager.

There's information online about this method: en.wikipedia.org/.../KCDSA

Sincerely,

Wyatt Keller

0 Coman Y over 3 years ago in reply to Wyatt Keller

Prodigy 120 points

Hello Wyatt,

Thank you very much for your reply.

1.The link（e2e.ti.com/.../2953159） still doesn't explain how to calculate 128bit key through key F（160bit）and key C(160bit).

2.What do the bqkeypackager expect from input? Do you have packaged ECC .bqk files that can program.

Sincerely,

Coman

0 Wyatt Keller over 3 years ago in reply to Coman Y

TI__Guru** 102455 points

Hello Coman,

Key F and key C are 2 sections of the private key as stated in the link. You program both keys.

You must set your own keys, we cannot supply you with a key to program. The packager will create the file that can then be used to program the gauge.

Sincerely,

Wyatt Keller

0 Coman Y over 3 years ago in reply to Wyatt Keller

Prodigy 120 points

Hello Wyatt,

Thank you very much for your reply.

Please help answer the questions in the word document. Thanks!

bz40z80_key_question.docx

Sincerely,

Coman

0 Wyatt Keller over 3 years ago in reply to Coman Y

TI__Guru** 102455 points

Hello Coman,

Please check the TRM for information on the authentication, in section 15.2.2 SHA-1 Authentication it gives the steps for authentication.

The ECC has to be done in 2 sections because the SMBus max number of bytes to send. You can check the TRM for how you want to send the bytes and what size each packet is.

Sincerely,

Wyatt Keller

0 Coman Y over 3 years ago in reply to Wyatt Keller

Prodigy 120 points

Hello Wyatt,

Thank you very much for your reply.

1. SHA1: I looked at TRM very carefully. It only mentioned that SHA1 authentication needs 128 bit key, but it didn't mention 160 bit Key F and Key C. So I don't know where 128 bit key comes from and how to use Key F and Key C.

2.ECC: My question has nothing to do with SMBus. What I don't understand is that in 163bit ECDSA, public keys is 42byte(84 hexadecimal numbers) in theory, but bq40z80 only needs 21byte(42 hexadecimal numbers). Is the ECC authentication of bq40z80 not ECDSA?

Sincerely,

Coman

0 Wyatt Keller over 3 years ago in reply to Coman Y

TI__Guru** 102455 points

Hello Coman,

The Key F is for factory, key C is for customer. The final private key is a combination of both, this is from legacy gauges. Programming the keys is simply broken into 2 sections because the max size limitations of SMBus.

In the TRM the output is the 160 bit digest, this is not an input. The TRM does not explain the authentication algorithm, it only shows how to implement it in the gauge.

You can use openSSL to generate the keys.

Sincerely,

Wyatt Keller

0 Wyatt Keller over 3 years ago in reply to Wyatt Keller

TI__Guru** 102455 points

Hello Coman,

There are also other forum threads explaining the authentication I would recommend: e2e.ti.com/.../3279096

Sincerely,

Wyatt Keller

0 Coman Y over 3 years ago in reply to Wyatt Keller

Prodigy 120 points

Hello Wyatt,

1. I know the process of SHA1 authentication, but I don't know how to combine Key F and Key C to get the final key.Key F and key C are 160bit respectively, but the final key is 128bit.

for example:

Key F = 0123456789ABCDEF0123456789ABCDEF01234567

Key C = FEDCBA9876543210FEDCBA987654321076543210

So the final key = ?

Sincerely,

Coman

0 Coman Y over 3 years ago in reply to Wyatt Keller

Prodigy 120 points

Hello Wyatt,

I have another question about ECC. I use bqKey Packager tool to package Key F + Key C and Public Key, and then use bqKey Programmer to program on bq40z80 EVM, but it prompts authentication error. What can I do to program ECC's key program into EVM.

Sincerely,

Coman

0 Wyatt Keller over 3 years ago in reply to Coman Y

TI__Guru** 102455 points

Hello Coman,

Some of the documents tools are used to support legacy gauges as well, for the bq40z80 I would not use the bqKeyPackager, you should use the bqStudio plugin.

There's a FAQ about how to use SHA1: e2e.ti.com/.../3279096

Sincerely,

Wyatt Keller

0 Coman Y over 3 years ago in reply to Wyatt Keller

Prodigy 120 points

Hello Wyatt,

Is there an example of ECC authentication using bqstudio plugin? Including how to write the ECC key.

Sincerely,

Coman

0 Wyatt Keller over 3 years ago in reply to Coman Y

TI__Guru** 102455 points

Hello Coman,

I'm checking some internal documents if I can share with you. Give me a couple days to find out.

Sincerely,

Wyatt Keller

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BQ40Z80EVM-020: ECC authentication