So KMS itself is not illegal – but the illegal part that you’re describing comes from installing a fake KMS server to provide licenses that you don’t actually own. (I don’t know the specifics of MS licensing, but selling ‘real’ KMS activations off a real server to third parties is most likely not permitted either.)

Is it safe to activate Windows with KMS?

No, it isn’t safe to use either kms activation or any other activation software, specially if they use (as you said) unknown host server beacause this will provide them a kind of backdore to your system by which they might track your files or sensitive information.

Are kms keys safe?

AWS KMS provides almost 100 percent of the durability of cryptographic keys. … AWS KMS is integrated with CloudTrail, which allows users to audit the purpose for which the key is used, when it was used, and by whom the key was used.