safety – What’s eciesEncryptionCofactorVariableIVX963SHA512AESGCM in iOS SecKeyCreateEncryptedData?

I’m this reply:

https://stackoverflow.com/a/53807793/1634905

When utilizing Elliptic Curve key pair, it has the next:

non-public let keyType = kSecAttrKeyTypeECSECPrimeRandom // kSecAttrKeyTypeECSECPrimeRandom
non-public let algorithm = SecKeyAlgorithm.eciesEncryptionCofactorVariableIVX963SHA512AESGCM
non-public let keySize = 384

The algorithm is used within the SecKeyCreateEncryptedData perform.

What’s eciesEncryptionCofactorVariableIVX963SHA512AESGCM right here?

Apple’s doc would not clarify it a lot:

https://developer.apple.com/documentation/safety/seckeyalgorithm/2874226-eciesencryptioncofactorvariablei

I see there are different attainable choices equivalent to eciesEncryptionCofactorVariableIVX963SHA384AESGCM. Why did that SO reply choose the one with SHA512 when it picked 384 because the keySize?