matrix-nio/tests/data/events/key_key.json

{
    "content": {
        "key": "fQpGIW1Snz+pwLZu6sTy2aHy/DYWWTspTJRPyNp0PKkymfIsNffysMl6ObMMFdIJhk6g6pwlIqZ54rxo8SLmAg",
        "transaction_id": "S0meUniqueAndOpaqueString"
    },
    "type": "m.key.verification.key",
    "sender": "@bob:example.org"
}