How to handle padding with STM32 Cryptographic Library

[Folmer Brem N�hr]

Posted on December 07, 2016 at 15:40

I am writing an application in C# that AES-encrypts some data that is then decrypted inside an STM32 using STM32 Cryptographic Library. My C#-class (

https://msdn.microsoft.com/en-us/library/system.security.cryptography.rijndael(v=vs.110).aspx

) can encrypt using different types of padding (ANSIX923, ISO10126, PKCS7 and with zeros). I have not found a way to specify the padding for the function in the 

STM32 Cryptographic Library.

Right now, my decryption fails because of padding-issues.

I use AES 128-bit, CBC-mode.

What padding is used in STM32 Cryptographic Library?

How to I change the padding mode?

Thanks

[Imen.D]

Posted on December 07, 2016 at 16:55

Dear

folmerbrem

‌,

Why do you need use the padding ?Would you please specify the message size that you want to encrypt ?

Best Regards

-Imen-

[Folmer Brem N�hr]

Posted on December 07, 2016 at 17:00

I need it as the data from the C# application is padded. It can choose between 

ANSIX923, ISO10126, PKCS7 and with zeros.

Is this something that I need to implement myself or is there some way to use padding inside the library?

The message size is anywhere from 16bytes to many megabytes

[Tesla DeLorean]

Posted on December 07, 2016 at 18:40

Are you using an STM32 with CRYPT hardware? A review of the hardware implementation should provide some insight.

Beyond simplistic implementation, you'd do a lot better compiling your own library from source you can understand and inspect.