AWS IoT broker how to register a client certificate 1024 bits key length?

Question

Hi,

We are trying to register a self signed X.509 for client authentication to aws iot core (aws iot register-certificate) but we get the error "The key in the certificate is not valid".  
The problem seems related to the length of the key, it's 1024 bits, we have no problems register a certificate with 2048 bits key. Signing algorithm is "SHA-256 with RSA".  
Here there is a note about the key length of the CSR request, no mention about the key length of a self-signed certificate:
https://docs.aws.amazon.com/iot/latest/developerguide/x509-client-certs.html

How can register a self signed certificate with 1024 bits key length?

Thanks in advance for support

Reason for this question:
We have an old device with few calculation resources, connection to the broker using a 2048 bits key length client certificate takes 10 secs, using a client certificate with 1024 bits key takes 4 seconds, we measured using another broker not aws iot.  We know 1024 bits key is not the best key but 10 seconds to connect is two much.

Accepted Answer

Hi,

the document you are referring to mentions: **The certificate signing request (CSR) must include a public key that is either an RSA key with a length of at least 2048 bits...**". So you cannot use a key with a smaller length than 2048 bits.

But you could try to use [custom authentication](https://docs.aws.amazon.com/iot/latest/developerguide/custom-authentication.html) with AWS IoT Core to achieve your goal.

Cheers,  
Philipp

AWS IoT broker how to register a client certificate 1024 bits key length?

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