[old] memo.cash protocol

[Karl]

I imagine people are using other chains now, but this protocol is
well-known due to a compromised web interface that exists.  It works
and is in use on the bitcoin variants.  I am not presently using it.

OP_RETURN is a bitcoin opcode for storing data politely.  Older
protocols use UTXO outputs for data storage, which is more robust but
makes every node keep the data in a live database rather than the
transaction archive.

These transactions can be generated programmatically the same way any
bitcoin transaction is generated.

This protocol specification has not changed since 2018 and is still in use.

Posting to a public blockchain should be done anonymously.

https://memo.cash/protocol

<h2>Protocol</h2>

<p>
    Protocol uses P2PKH addresses.
    Actions are saved using <b>OP_RETURN</b>.
</p>

<p>
    Message data is UTF-8 encoded. For example, this action would set
your name to "memo":
</p>

<pre style="font-family:monospace">OP_RETURN 6d01 6d656d6f</pre>

<h3>Action Codes</h3>

<table class="table">
    <thead>
    <tr>
        <th>Action</th>
        <th>Prefix</th>
        <th>Values</th>
        <th>Status</th>
        <th>Example</th>
    </tr>
    </thead>
    <tbody>
    <tr>
        <td>Set name</td>
        <td>0x6d01</td>
        <td>name(76)</td>
        <td>Implemented</td>
        <td>
            <a class="btn btn-leave" target="_blank"
               href="https://explorer.bitcoin.com/bch/tx/753e29e81cdea12dc5fa30ca89049ca7d538d4062c4bb1b19ecf2a209a3ac8d9">
                Block Explorer
            </a>
        </td>
    </tr>
    <tr>
        <td>Post memo</td>
        <td>0x6d02</td>
        <td>message(76)</td>
        <td>Implemented</td>
        <td>
            <a class="btn btn-leave" target="_blank"
               href="https://explorer.bitcoin.com/bch/tx/c7e91099923a28cf86685c9683c74c8c029c8965a5039f84ad79886b42720f9b">
                Block Explorer
            </a>
        </td>
    </tr>
    <tr>
        <td>Reply to memo</td>
        <td>0x6d03</td>
        <td>txhash(20), message(53)</td>
        <td>Planned</td>
        <td></td>
    </tr>
    <tr>
        <td>Like / tip memo</td>
        <td>0x6d04</td>
        <td>txhash(20)</td>
        <td>Implemented</td>
        <td>
            <a class="btn btn-leave" target="_blank"
               href="https://explorer.bitcoin.com/bch/tx/b7b9376659920ecbaad794bfb1cd0a5da095f9231fe1f4243474c9606623fc14">
                Block Explorer
            </a>
        </td>
    </tr>
    <tr>
        <td>Set profile text</td>
        <td>0x6d05</td>
        <td>message(76)</td>
        <td>Planned</td>
        <td></td>
    </tr>
    <tr>
        <td>Follow user</td>
        <td>0x6d06</td>
        <td>address(35)</td>
        <td>Implemented</td>
        <td>
            <a class="btn btn-leave" target="_blank"
               href="https://explorer.bitcoin.com/bch/tx/7958e54680a4ed01316ce99489f54c26234060c0a18d5ffc4d4d44182e1a2891">
                Block Explorer
            </a>
        </td>
    </tr>
    <tr>
        <td>Unfollow user</td>
        <td>0x6d07</td>
        <td>address(35)</td>
        <td>Implemented</td>
        <td>
            <a class="btn btn-leave" target="_blank"
               href="https://explorer.bitcoin.com/bch/tx/a9987c7643a3d5a033b2630cf7e3603385b7ab6ec7b6be690f37b9a58c780acd">
                Block Explorer
            </a>
        </td>
    </tr>
    <tr>
        <td>Set image base url</td>
        <td>0x6d08</td>
        <td>url(76)</td>
        <td>Planned</td>
        <td></td>
    </tr>
    <tr>
        <td>Attach picture</td>
        <td>0x6d09</td>
        <td>txhash(20), imghash(20), url(34)</td>
        <td>Planned</td>
        <td></td>
    </tr>
    <tr>
        <td>Set profile picture</td>
        <td>0x6d10</td>
        <td>imghash(16), url(61)</td>
        <td>Planned</td>
        <td></td>
    </tr>
    <tr>
        <td>Repost memo</td>
        <td>0x6d11</td>
        <td>txhash(20), message(63)</td>
        <td>Planned</td>
        <td></td>
    </tr>
    <!--
    <tr>
        <td>Testing</td>
        <td>0x6d00</td>
        <td>data(76)</td>
        <td></td>
        <td></td>
    </tr>
    -->
    </tbody>
</table>

<p>
    Additional actions being considered:
</p>

<ul>
    <li>Tagging users in posts</li>
    <li>Voting</li>
    <li>Issue and revoke delegated addresses</li>
    <li>Dislike and/or flag posts/users</li>
</ul>