Magic bytes and ports

Pearl isn’t one network but several: the real one, mainnet, plus test networks whose coins are worthless. They run the same software. Something has to keep them from mixing, so that a test block never ends up on the real chain.

In Bitcoin, that something is the magic bytes: four bytes that open every message, saying which network it belongs to. Pearl has magic bytes too, “PRLM” for mainnet. But you will never see them on the wire. Pearl encrypts every connection, so the magic does its job in a quieter place.

Try it

Type 50524C4D as hex and flip the byte order. You get 4D4C5250: the same number, stored the way pearld stores it.

What are Pearl’s magic bytes?

Each network has a 4-byte number, chosen so that its hex spells letters:

0x50 0x52 0x4C is ASCII for “PRL”, and the last byte names the network: M for mainnet, 1 and 2 for the testnets, R for regtest, S for simnet. Signet’s magic is derived from a hash of its challenge script instead, as in Bitcoin.

Why are the bytes backwards?

Because pearld writes the magic as a 4-byte little-endian number, smallest byte first, exactly as Bitcoin does with its own magic (0xD9B4BEF9, written f9 be b4 d9). So 0x50524C4D becomes 4d 4c 52 50, which as ASCII reads “MLRP”. Byte order is explained on byte order.

Where do the magic bytes appear?

Not on the network. Pearl peers only speak BIP-324 encrypted transport, and BIP-324 messages have no plaintext header at all: no magic, no command name, no checksum. To anyone watching, a Pearl connection is a stream of random-looking bytes.

The magic shows up in two places instead:

• In the key derivation. When two nodes set up encryption, they turn their shared secret into keys with HKDF, salted with the text pearl_v2_shared_secret followed by the magic’s four bytes.
• On disk. pearld’s block files store each block after the network’s magic, as Bitcoin nodes do.

Here is mainnet’s salt, as pearld builds it:

Then how are networks kept apart?

By that salt. A mainnet node and a testnet node that connect by mistake each derive their encryption keys with their own magic in the salt: 4d4c5250 against 314c5250. Their keys don’t match, so neither can decrypt the other, and the connection fails before a single real message. In Bitcoin’s old v1 protocol the same job is done by checking the magic at the start of each message; in Pearl it is done by cryptography.

Each network also has its own ports, its own genesis block and its own address prefix (prl1… on mainnet, tprl1… on testnet), so even outside the wire protocol the networks rarely look alike.

Which ports does Pearl use?

On mainnet:

Peer-to-peer

44108

open to the internet for incoming peers

pearld RPC

44107

local commands; keep it private

Oyster wallet RPC

44207

the wallet daemon

A node only needs the P2P port open to accept incoming peers. It can run perfectly well with only outgoing connections; it just won’t be listed by the DNS seeds, which only hand out nodes reachable on 44108.

MainNet  PearlNet = 0x50524C4D // "PRLM" in ASCII
RegTest  PearlNet = 0x50524C52 // "PRLR" in ASCII
TestNet  PearlNet = 0x50524C31 // "PRL1" in ASCII
TestNet2 PearlNet = 0x50524C32 // "PRL2" in ASCII
SigNet   PearlNet = 0x40CF030A
SimNet   PearlNet = 0x50524C53 // "PRLS" in ASCII

salt := []byte("pearl_v2_shared_secret")
var magic [4]byte
binary.LittleEndian.PutUint32(magic[:], uint32(net))
salt = append(salt, magic[:]...)