TM4C129XNCZAD: AES Encryption/Decryption

Fehan Malik

Part Number: TM4C129XNCZAD

I have implemented AES Encryption using the TM4C129XNCZAD hardware AES Module. I wanted to verify if the output generated by the micro hardware AES Modules matches with the Online AES Calculate. While different AES Online calculators have the same output, the one generated using the AES Hardware Module itself is different then online AES Calculator.

Am I doing something wrong or is it by design?

over 6 years ago

0 Fehan Malik over 6 years ago

Intellectual 550 points

For example this is the data I used to create Encryption of the TI example using online calculator.

extranet.cryptomathic.com/.../index

0 Ralph Jacobi over 6 years ago in reply to Fehan Malik

TI__Guru*** 135355 points

Hello Fehan,

How are you configuring the AES module? Have you checked that your calculator is reflecting the exact AES mode being used by the TM4C device?

0 Fehan Malik over 6 years ago in reply to Ralph Jacobi

Intellectual 550 points

Ralph,

I used this example : e2e.ti.com/.../1345618

This uses CBC Mode, IV Vector and 64 byte data. It also give the expected output which I verified using the AES alogrithm.

Now when I feed the same input into the Online Calculator, I get the different result. Kindly see the result here: extranet.cryptomathic.com/.../index

0 Ralph Jacobi over 6 years ago in reply to Fehan Malik

TI__Guru*** 135355 points

Hello Fehan,

I can't run the example immediately but at a quick glance it looks like the IV Vector is working in a big endian mode. Have you tried seeing if the result on the calculator is correct if you instead input the CBC as '000102030405060708090A0B0C0D0E0F'? (hopefully the key doesn't have to be adjusted like this as well...)

I'll load the example up later today and run it to try and uncover what's going on if you don't find the answer from my above suggestion.

0 Ralph Jacobi over 6 years ago in reply to Ralph Jacobi

TI__Guru*** 135355 points

Hello Fehan,

I was right about my assumption, and reserving the order of the bytes has to be done for all inputs. This shows the correct result:

See Appendix F.2 of this document for reference as that is where the example was pulled from (the E2E post code was just a condensed version of our aes128_cbc_encrypt example on TivaWare): https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38a.pdf

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TM4C129XNCZAD: AES Encryption/Decryption