Hash values in photo._master_record["fields"]["resOriginalRes"]["value"]

[takeru]

The problem

value = photo._master_record["fields"]["resOriginalRes"]["value"]

In the value
to
'fileChecksum'
'wrappingKey'
'referenceChecksum'
What is the meaning of these hash values?
I want to check the checksum of a downloaded file.
I wish I knew the algorithm and encoding, but does anyone know?

Environment

• pyiCloud release with the issue (pip show pyicloud): 1.0.0
• Last working pyiCloud release (if known):
• Service causing this issue:
• Python version (python -V): Python 3.10.8
• Operating environment (project deps/Docker/Windows/etc.): Mac

Traceback/Error logs

Checklist

• I've looked informations into the README.
• I've looked informations into the pyiCloud's code.
• I've looked informations in Google.

Additional information

[takeru]

https://developer.apple.com/library/archive/documentation/DataManagement/Conceptual/CloudKitWebServicesReference/Types.html

Asset Dictionary

An asset dictionary represents an Asset field type with the following keys:

Key	Description
fileChecksum	The signature of a file returned from the file upload step. This key is required for the public and private database.
size	The size of the file, calculated by the asset upload step. This key is required for the public and private database.
referenceChecksum	The checksum of the wrapping key returned from the upload step. This key is required for the private database.
wrappingKey	The secret key used to encrypt the asset. This key is required for the private database.
receipt	The receipt for uploading the asset, described in Upload Asset Data. This key is required for the public and private database when saving the enclosing record.
downloadURL	The location of the asset data to download. This key is present only when fetching the enclosing record.

Asset Dictionary An asset dictionary represents an Asset field type with the following keys:

https://developer.apple.com/library/archive/documentation/DataManagement/Conceptual/CloudKitWebServicesReference/UploadAssets.html

I don't know the details, it seems to be returned when uploaded.

[takeru]

sample_photos = []
for _photo in api.photos.all:
    sample_photos.append(_photo)
    if 10<=len(sample_photos):
        break


import base64

for index, photo in enumerate(sample_photos):
    # print(json.dumps(photo._master_record,indent=2))
    print(f"[{index}]")
    
    fileChecksum = photo._master_record["fields"]["resOriginalRes"]["value"]["fileChecksum"]
    downloadURL = photo._master_record["fields"]["resOriginalRes"]["value"]["downloadURL"]
    print("curl -o '%s_%s' '%s'" % (fileChecksum.replace("+","-").replace("/","_"), photo.filename, downloadURL))

    b64 = fileChecksum
    print(b64)
    bin = base64.b64decode(b64)
    print(bin)
    hx = bin.hex()
    print(hx)

    print(len(hx))
    print("")

When I decode base64 to hex, the first byte seems to be fixed at 01. Is this a version of the hash algorithm?
Is it something like 20byte = 160bit algorithm?