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I have learned that the certificate is something that contain information about a public key. An article on wikipedia says Public Key Certificate as well. If we are talking about private key, it's not a certificate, but a key that corresponds with the public key certificate.

On Microsoft Azure I have found this sentence:

Private key certificates (.pfx) can be used for TLS/SSL bindings and can be loaded to the certificate store for your app to consume.

I thought that certificates are always public and the .pfx file format just contains both the public key certificate and the corresponding private key.

Is this correct to say private key certificate?

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Generally speaking certificates (X.509) contains the public key (of the corresponding private key) that was used to sign the certificate. You can't make any inferences of authenticity of the certificate (and it's attributes) if there is no signature or public key. I suspect your difficulty has to do with how the certificate and keys are distributed.

Certificates are encoded in various formats e.g. DER, PEM and stored in various containers e.g. PKCS12. If you want to store the private key with the certificate you will need to choose a container that supports that like PKCS12 & PFX.

Therefore I don't think the term private key certificate is correct.

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  • That's what I thought as well. Most people I speak to use this term though it is not quite correct, but I was surprised Microsoft did that Oct 9, 2020 at 9:23
  • Indeed "private key certificate" is not standard terminology, and further is actively harmful terminology in that a certificate is something you're expected to present to another party, while a private key is something that must never be shared with another party. "Corresponding private key" is the correct term that should always be used. Formats that bundle both should never be used because of a risk of transmitting the private key unintentionally. Oct 9, 2020 at 17:05

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