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.