In say a 2 of three multi-sig setup, do such non-public keys (base 58 and even Hexadecimal) exist beneath the hood.

Any cryptographic key of any sort, Bitcoin or different, on a pc, is representable in hexadecimal, in octal, in binary, in base58, in base64 and in another illustration used on computer systems. The keys are simply numbers and the assorted encodings listed are simply completely different visible representations of the identical quantity.

From what I’ve learn, a multisig setup makes use of the non-public and public keys which are usable for abnormal transactions.

In https://en.bitcoin.it/wiki/Multi-signature it says:

Making a multi-signature tackle with Bitcoin-Qt

A 2-of-3 multisig tackle might be created by following these steps:

1. Collect (or generate) 3 bitcoin addresses, on whichever machines will probably be taking part, utilizing getnewaddress or getaccountaddress RPC instructions (or copy and paste from the GUI).

2. Get their public keys utilizing the validateaddress RPC command 3 occasions.

3. Then create a 2-of-3 multisig tackle utilizing addmultisigaddress; e.g.,

   bitcoind addmultisigaddress 2 '["044322868cb17d64dcc22185ae2d4493111d73244c3668f8ac79ecc79c0ba8d30a6756d0fa20157 709af3281cc721c7f53321a8cabda29b77900b7e4fe0174b114","..second pubkey..","..third pubkey.."]'
   

   addmultisigaddress returns the multi-signature tackle. Be slightly cautious, the general public keys are uncooked hexadecimal and do not comprise checksums like bitcoin addresses do. You may then ship funds into that 2-of-3 transaction utilizing the conventional sendtoaddress/sendmany RPC instructions, or the GUI (or something that is been up to date to acknowledge multisig addresses)

I feel that the advised use of getnewaddress in the first step reveals that keys used are those we’re conversant in from abnormal single-key transactions.