private key for shared AirTags (only key provided is peerTrustSharedSecret)

[robertsmd]

The decrypted plist for an AirTag that has been shared with me is below. This is incompatible with the current library due to not having a private key. Yes, I've tried using the peerTrustSharedSecret as the private key, it doesn't work as-is.

Seems like a good way to implement this would be to examine the traffic to Apple servers when examining the location of a shared AirTag via the FindMy application. It may use a different endpoint for an intermediary step between peerTrustSharedSecret and privateKey.

Does anyone know how to get the privateKey for these devices that are shared?

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>cloudKitMetadata</key>
	<data>
	#Base64 blob here#
	</data>
	<key>communicationsIdentifier</key>
	<dict>
		<key>ids</key>
		<dict>
			<key>correlationIdentifier</key>
			<string>#uuid (unknown what it is) here#</string>
			<key>destination</key>
			<dict>
				<key>destination</key>
				<string>mailto:#Owner email here#</string>
				<key>type</key>
				<integer>0</integer>
			</dict>
		</dict>
	</dict>
	<key>displayIdentifier</key>
	<string>#Owner email here#</string>
	<key>identifier</key>
	<string>#baUUID here#</string>
	<key>peerTrustSharedSecret</key>
	<dict>
		<key>key</key>
		<dict>
			<key>data</key>
			<data>
			#INSERT KEY HERE#
			</data>
		</dict>
	</dict>
	<key>type</key>
	<integer>1</integer>
</dict>
</plist>

[robertsmd]

length of peerTrustSharedSecret is 44 base64'ed or 32 raw. This is the same as the sharedSecret and secondarySharedSecret.