What is the Channel ID in 1ML.com?

Question

To look up information of a channel on 1ML.com, I wonder how the channel_id is built.

Reading this question and the corresponding BOLT02, I see that

channel_id = funding_txid XOR funding_output_index

As the funding_txid is a 32 byte string (e.g. 399986f8d47b36d4f21c07de0ce7d422de244ed58a72e6b44d26985fe1e7465c), the channel_id has also 32 bytes.

However, when looking at a specific channel at 1ML.com, the channel_id is much shorter (e.g., 735416048958177281).

Hence my question is:

• Is the above definition of the channel_id correct? If so, what is the difference to the one of 1ML.com?
• Otherwise: How is the channel_id computed correctly?

Answer 1

The channel_id in 1ml seems to be the lnd encoding of the short_channel_id. Note that the short Channel ID is just 3 bytes of blockheight, 3 bytes of transaction index within the and 2 bytes for the output index within the transaction. While BOLTs recommend to serialize this as HEIGHTxINDEXxOUTPUT lnd just concatenated those 8 bytes and displays them as a single large integer. I guess since lightning explorer tend to take over the APIs of implementations we have this confusion