Hi, thanks a lot for the fast reply and sorry for my late answer but I did a lot of tests in order to solve the problem (I never had success on compute shared function when "talking" with another peer). Yes, you're right, no need to modify anything. The issue was that mbedtls uses ecp point coordinates in big endian format while the other peer bytes were intended to be in little endian format. After reversing the bytes before compute shared everything worked! Thank you, have a nice day! Brian

3 mag 2021, 21:53 da mbed-tls@lists.trustedfirmware.org:

Hi Brian,

It's not clear to me what you're trying to do. Mbed TLS supports Curve25519 arithmetic for X25519, accessible through the mbedtls_ecdh_xxx interface. If you want to use Curve25519 for some other purpose, this may or may not be supported via direct access to the mbedtls_ecp_xxx interface. The curve arithmetic code only supports predefined groups, it does not support changing the generator without patching the library.

For Curve25519, the generator is the point (X,Z)=(9,1). Isn't this the generator you want?

Best regards,

-- Gilles Peskine Mbed TLS developer

On 30/04/2021 17:39, Brian via mbed-tls wrote:

...

Hi all, I'm trying to set the generator g to a value of 9 for the Curve25519 with mbedtls_ecp_gen_key function. However I cannot find any way to accomplish that. Could anyone help me? Thank you, have a nice day,Brian

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