Hi François,

Thanks for responding. Apologies for not including context. I'm using esp-idf v6 which includes mbedtls 4.0. My "application" is a re-usable library that obtains certificates using ACME.

I saw the field in the class definition. I get from your reply it's ok for me to use it.

So let me ask a noob question. How do I use this to produce strings in C or C++ code ? The mbedtls_x509_authority structure consists of buffers in something other than such C/C++ string formats.

    Danny

On 6/19/26 13:22, Francois Mace wrote:
Hello Danny,

What is the version of mbed TLS you are using?

I think latest version expose AKI with

mbedtls_x509_authority authority_key_id;

as a member of the  mbedtls_x509_crt class.

Best regards,

François



Le jeu. 18 juin 2026 à 18:05, Danny Backx via mbed-tls <mbed-tls@lists.trustedfirmware.org> a écrit :

Hi,

How can I extract the AKI (Authority Key Identifier) from a certificate using mbedtls ?

I could parse the certificate file itself, I guess, but isn't that what mbedtls does?

Thanks,

    Danny

https://www.rfc-editor.org/info/rfc5280#section-4.2.1.1


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