Intro

Allbridge Core is a cross-chain swap built specifically for dollar-pegged tokens (stablecoins). Operates without wrapping tokens and works by keeping liquidity pools for the supported tokens on each blockchain. Incoming tokens go into the pool, the value of those tokens is sent via the messaging protocol to another chain, where it is converted back to the tokens to be paid to the user.

In detail, when the user sends tokens via the Allbridge Core the following happens:

• Bridge exchanges incoming tokens into their dollar value in the token pool for this particular token
• This value is send via the underlining messaging protocol to the destination chain
• Bridge contract on the destination chain swaps dollar value to the tokens from the liquidity pool and sends them to the recipient

This process is illustrated for a sample swap of USDT on Ethereum to BUSD on BNB Chain in the diagram below.

The user (or the protocol integrating Allbridge Core) only has to trigger a single transaction on the source chain (line #1 in the diagram above).

Details

Blockchains and tokens

Allbridge Core currently supports the following chains and tokens:

Blockchain	Contract Type	Address
Ethereum	Bridge	0x609c690e8F7D68a59885c9132e812eEbDaAf0c9e
USDC	Pool	0xa7062bbA94c91d565Ae33B893Ab5dFAF1Fc57C4d
USDT	Pool	0x7DBF07Ad92Ed4e26D5511b4F285508eBF174135D
BNB Chain	Bridge	0x3C4FA639c8D7E65c603145adaD8bD12F2358312f
USDT	Pool	0xf833afA46fCD100e62365a0fDb0734b7c4537811
Tron	Bridge	TAuErcuAtU6BPt6YwL51JZ4RpDCPQASCU2
USDC	Pool	TP5bMjDTFzHq7wwNij1JvbNgt3TmBhswfS
USDT	Pool	TAC21biCBL9agjuUyzd4gZr356zRgJq61b
Solana	Bridge	BrdgN2RPzEMWF96ZbnnJaUtQDQx7VRXYaHHbYCBvceWB
USDC	Pool Token Account	G6Qo3WW7RbWpSmACAocTBVgx6JW5kgRpUhABphEoDMfP
Polygon	Bridge	0x7775d63836987f444E2F14AA0fA2602204D7D3E0
USDC	Pool	0x4C42DfDBb8Ad654b42F66E0bD4dbdC71B52EB0A6
USDC.e	Pool	0x58Cc621c62b0aa9bABfae5651202A932279437DA
USDT	Pool	0x0394c4f17738A10096510832beaB89a9DD090791
Arbitrum	Bridge	0x9Ce3447B58D58e8602B7306316A5fF011B92d189
USDC	Pool	0x690e66fc0F8be8964d40e55EdE6aEBdfcB8A21Df
USDT	Pool	0x47235cB71107CC66B12aF6f8b8a9260ea38472c7
Avalanche C-Chain	Bridge	0x9068E1C28941D0A680197Cc03be8aFe27ccaeea9
USDC	Pool	0xe827352A0552fFC835c181ab5Bf1D7794038eC9f
USDT	Pool	0x2d2f460d7a1e7a4fcC4Ddab599451480728b5784
Base	Bridge	0x001E3f136c2f804854581Da55Ad7660a2b35DEf7
USDC	Pool	0xDA6bb1ec3BaBA68B26bEa0508d6f81c9ec5e96d5
OP Mainnet	Bridge	0x97E5BF5068eA6a9604Ee25851e6c9780Ff50d5ab
USDC	Pool	0x3B96F88b2b9EB87964b852874D41B633e0f1f68F
USDT	Pool	0xb24A05d54fcAcfe1FC00c59209470d4cafB0deEA

Messaging protocols

Allbridge Core uses messaging protocols to move information between blockchains. Particularly it is used to send information about transfers and their value to the recepient's blockchain. Allbridge Core architecture allows support for multiple messaging protocols. Currently supported protocols are:

• Wormhole is a decentralized protocol operated by Jump Crypto and used by their own Portal Bridge. Does not support Tron.
• Allbridge own messaging protocol which is less decentralized (just 2 validators), but works with all blockchains Allbridge Core supports, including Tron.

Wormhole protocol is more decentralized, this is why it is used by default. Allbridge messaging however is quicker (less time required to reach consensus), less expensive (smaller transactions) and supports Tron.

Fees

Allbridge Core fees can be divided into two distinct categories: fixed transaction fee not depending on the transfer amount and value adjustment fees.

Transaction fee

To pay for the receiving transactions on the destination chain, the user pays a transaction fee. It is paid in the gas coin of the sending chain and is attached to the transaction the user submits. It does not depend on the transfer amount.

Value adjustments

These adjustments affect the final amount received by the user. They include:

• Dollar value of the sending token, if more than 1 the amount will increase
• Source chain liquidity provider fee, always 0.15% of the transfer amount
• Dollar value of the receiving token, if more than 1 the amount will decrease
• Destination chain liquidity provider fee, always 0.15% of the transfer amount

To summarize, the user always pays 0.3% to the liquidity providers, the rest is the token value fluctuations explained below.

Token value

When transferring tokens between blockchains the amount need to be converted into their internal dollar value. This value depends on the pool condition and the amount being evaluated.

For the sending side (converting tokens into their value):

$$x = x_{orig} + x_{tokens}$$

$$y = \frac{\sqrt{4ad^3x + (4adx - 4ax^2 - dx)^2} + 4adx - 4ax^2 - dx}{8ax}$$

$$y_{value} = y_{orig} - y$$

Where:

• $x_{orig}$ is the token balance in the pool before swap (tokenBalance view function in the Pool contract)
• $x_{tokens}$ is the amount of tokens you plan to swap
• $y_{orig}$ is the value balance in the pool (vUsdBalance view function in the Pool contract)
• $a$ is a swap curve shape constant (a view function in the Pool contract, does not change)
• $d$ is a measure of the total liquidity in the pool (d view function in the Pool contract, does not change unless liquidity is added or removed)
• $y_{value}$ is the resulting dollar value of the $x_{tokens}$ tokens

For the receiving side (converting value into tokens the formula is very similar, but reversed):

$$y = y_{orig} + y_{value}$$

$$x = \frac{\sqrt{4ad^3y + (4ady - 4ay^2 - dy)^2} + 4ady - 4ay^2 - dy}{8ay}$$

$$x_{tokens} = x_{orig} - x$$

The meaning of the variables is the same as before, but for the token pool on the receiving side.

Integrating Allbridge Core

The easiest way to integrate Allbridge Core into your product is to use Core SDK (npm package, source).