HOM Coin : Efficient Blockchain based real estate

Stablecoin, database, and smart contract for buying and selling houses efficiently.

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At a Glance: * Stablecoin - kept at $1000 each * ERC20 token * Built in escrow system * Trade to/from Ethereum through the smart contract * Database of every home ever purchased with itGithub: contract version, source included):

Test Smart Contracts

About HOM Coin

HomesCoin is a cryptocurrency and decentralized database focused on real estate, which allows quick and seamless buying of homes.

Most transfers complete within 8 to 30 seconds, and are thus far faster than any large bank transfer. Expensive homes can be paid for just as fast as a cup of coffee.

As a decentralized database, it functions as a way to store information about houses online.  Unlike centralized databases, it cannot be taken offline, and it can be accessed from anywhere.  The information on the database is still trustworthy however, because only the contract owner can add or modify entries in this database.

Unlike most other cryptocurrencies, the HOM coin has a fixed price.  Nobody wants to sell a home with other cryptocurrencies because they don't know what the currency will be worth when the buy completes, so I decided that each HOM coin is worth $1000.

How is the coin kept stable?

HOM Coin has the ability to be its own exchange, where the price is set at a certain amount of Ethereum.  A user can convert Ethereum to HOM Coin (or vice versa) through the HOM Coin smart contract. The price of ethereum changes though, so the price in ethereum has to change to keep the price in dollars stable.  To handle this, the price is changed by an oracle program. Each buy or sell executed on the contract has a very small fee which is sent to this oracle program. This program watches the price of Ethereum and ensures that the HOM Coin price is $1000 constantly.

This small fee is less than a cent, but multiple buys and sells provides the oracle program enough Ethereum to function.  The oracle only needs a few cents to change the price. The oracle needs that few cents to pay Ethereum's transaction fees.  As the oracle program gets more funds, the fee drops. Once the oracle program has a certain amount of Ethereum, the fee is fractions of fractions of cents.  This cutoff is only worth a few dollars, so it would be met very quickly if there were even small amounts of trading volume on the HOM Coin smart contract.

If any exchange tried to sell HOM Coin at a different price then traders would take advantage of the opportunity, and buy from the cheaper source and sell to the more expensive one, correcting the market.

If the HOM Coin smart contract ran out of HOM Coin or Ethereum, the price would be able to change, but not for long.  HOM Coin can be minted or destroyed, so the market can be inflated or deflated. This shouldn't be needed because the HOM Coin contract would have very very large amounts of HOM Coin, and selling it would give it very large amounts of Ethereum.


HOM Coin exists on the Ethereum blockchain, so it has the same level of security Ethereum does.  Hypothetically, there could be a bug in the smart contract that would make it vulnerable to attack, but this is extremely unlikely.  The prototype HOM Coin contract has already been through many test versions, and the most sensitive logic is very simple, so has less room for security holes.  The biggest security risk is the HOM Coin controlling account. If an attacker gains access to the account, they would have complete control of the token. This can be avoided by storing the account on a hardware wallet with a password.  At that point the attacker would need to physically locate and steal the hardware wallet, then obtain the password. This effort is nearly impossible.

The next biggest hole is the oracle program, which controls the token price.  This program has an Ethereum account as well, but it cannot be put on a hardware wallet.  The oracle program needs untethered access to the Ethereum account. The easiest way of attacking this program is by attempting to disconnect it from the Ethereum network, making price...

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  • New test smart contract

    Dylan Brophy07/27/2019 at 15:43 0 comments

    I've made a new test contract on the Ropsten testnet.

    You can see it and interact with it here:

    Yeet! :)

  • Adding The Obvious

    Dylan Brophy07/14/2019 at 06:37 0 comments

    Why didn't I add buying and selling functionality yet?  Isn't this an obvious step?

    When I first started working on this, that sounded really daunting and complex, not because of programming, but for the legal and security implications.  How can it be integrated into the existing legal system?  What if someone places a sell for a house they do not own?

    I'm not a lawyer.  Nor a realtor.  I'm an engineer, and a programmer.  I'm not going to concern myself with these issues much yet, and instead focus on creating a more useful and capable smart contract.

    So, I came up with this process:

    1. Seller asks to place an offer, providing proof of ownership and any other required legal documents, specifying an offered escrow time

    2. An entry is placed on the blockchain by the smart contract's database owner after a proper inspection is passed

    3. Buyer accepts offer, signs documents electronically, and pays.

    4. When escrow is over, the smart contract allows the seller to claim the HOM Coin paid in the contract

     * The buyer may cancel before escrow is over as well, in which case the payment is refunded.

    I'm sure there are plenty of things I may have left out, or things that could be better, but I am still working on this aspect.  I would say that this is a step up from not being able to buy houses with this contract at all.

    You'll notice that realtors are not included.  I don't really think they are necessary.  If you want to contact the seller to make a counter offer, the smart contract contains contact information, and the seller can cancel the offer and request an updated one.  All houses would need to be inspected before being put on this market.

    I plan on asking my colleague, who is a licensed realtor, more about this.  I'm working with him on this project.

  • Hacked Test Contracts!!!! (Interesting Story)

    Dylan Brophy07/01/2019 at 01:15 0 comments

    Someone (or multiple people) have been exploiting bugs in my test contracts!

    I actually think it's pretty funny, I already fixed these bugs but the old contracts do not reflect the fixes.  I have no idea who did this.

    So what did they do?

    The bug lies in this piece of code here:

    function setOracleAddress(address payable adr) public {
    	oracle_adr = adr;

     The bug has been fixed for a while now, but the contracts on the blockchain have this old function.  It does not check to see if the sender of the transaction is indeed the owner, so anyone can change the oracle address.

    The oracle controls the price, so anyone can now change the price and receive the fees.  If they can change the price, they can buy coins at zero and sell them at any price they want (essentially allows stealing from the contract)

    Lets follow what they did on the contract 0x1574ea34e90db0618c343e6e64a31e03c40383c9

    This is a contract actually on mainnet, so it had real Ethereum in it to be stolen.

    At transaction 0x5a606944e75c9c45cfc83810980f94035beb8005887e00b3063d16705906640c, the ethereum account 0xcd7038aff3cd202afc998f655575510424170862 changed the oracle address of my smart contract to 0x43ee0c8e212a3d21c6924159ae7b834e9105d27e.

    In essence, this is the attacker taking the Oracle address.

    The attacker then changed the price of the token to zero (transaction 0x22d03975e23348e62612fd54733c0f5d01110423115cdb5f17c99e8eef95d182)

    Then, this person bought 10% of the tokens for zero ethereum, essentially stealing the tokens. (0x8a2eb797567cbbc79467ad73e3f800c368fda60b8164d34c7dd618bcdb52493b)

    It gets better:  the attacker can now steal real ethereum by increasing the price manually.

    Our attacker chose to set the price at 1 Ethereum = 1 HOM Coin (0x379b936ac73ced7155b9643a3de3c05ad71f5f957222b65338b4d1df8290bca1)

    And, the last step:  sell some stolen tokens.  Since the price was set to one, selling the same amount of tokens as the balance of the smart contract will steal the entire smart contract balance.  That's exactly what happened at transaction 0x5534a39ad4ce457ce7b16d76e3f5fefbeb0c58bddf87b3ed25ea8a4bea84dc97.

    Whoever this was, he/she was nice enough to send me back all the stolen Ether, but they still have 10% of the tokens. :P   See the token holder pie chart here, with our attacker having that 10%.

    What contracts did they hack?  Here are the one's I've found that are exploited:

    I don't think there are any others, but I can't really be sure.  I don't even know if these contracts were hacked by the same person (although they probably were).

    This was actually really exciting for me because I've never had anyone actually interact with my projects, especially not in a way like this.  It's like someone just walked up and had a conversation with something I built.  Granted, they manipulated the project, but still;  It's really cool!

  • Separation of Powers

    Dylan Brophy06/27/2019 at 19:24 0 comments

    I'm breaking the contract into two sections, each with a different 'owner' account.

    Why?  If something were to go wrong with one of the accounts (lost, hacked, stolen, etc), at least the attacker would not have access to the entire contract.  Furthermore, half of the contract would still work fine.

    How I've already done this a little bit:

    HOM Coin has an Oracle program that keeps it's price steady.  The Oracle account is separate from the owner account.

    I thought about the possibility of someone gaining unauthorized access to either account.  In this case I want one to be useless without the other, so that access must be gained to both.  So I changed some things:

    • Changing the oracle program account requires the permission of the Oracle account itself
    • If the owner destroys the contract then the oracle get's all of the contract's Ethereum

    Attacker tries to destroy the contract to get the Ether?  Nope, Oracle gets it.  Wants to manually manipulate the price by accessing the oracle?  Oracle address can be changed, and the owner cannot change the oracle account without already having the oracle.

    Attacking the contract is now like one of those movies about collecting 'all' of the stones or artifacts or something.  Really cool!

  • Stepping Towards Better Security (avoiding overflows)

    Dylan Brophy06/24/2019 at 22:38 0 comments

    The security in the original HOM Coin smart contract wasn't terrible, except that it didn't check for overflows.  If this is to be a popular coin then it can't have problems like that.

    The problem with overflows

    Anyone reading this on hackaday should understand the idea of an overflow - in computers, sometimes when a mathematical operation is executed, the result does not fit in the finite space the result can store.

    With smart contracts, this can allow hackers to steal real money.  Lets say we have this psudocode as a function to send tokens to someone:

    function transfer(sender, receiver, uint8_t amount){

    This should work fine, right? Nope.  Let's say Alice has 200 tokens and sends 128 of them to Bob who has 128 tokens.  in this case, Bob's balance would become zero because 128+128 = 256, but 256 doesn't fit (used 8 bit unsigned values).  In essence, Alice just destroyed all of Bob's coins!  There are many ways problems like this can exists, and an Ethereum contract needs to be especially careful, because real money can be lost.

    Essentially I fixed security bugs like this, but there are also other security concerns.  The owner of the HOM Coin contract can destroy the contract (taking all the ether in the contract as well), or change the Oracle program's Ethereum address.  This is fine, unless the private key to the owner account is somehow stolen.  In this case the thief would be able to freely manipulate the HOM Coin price, or destroy the coin entirely, taking large sums of Ether.  No good.

    I made a change so that the oracle address can only be changed once the last oracle address has confirmed that the change is allowed.  This way, two private keys would need to be stolen for price manipulation.

    I still need to find a way to make contract destruction trustless.  Perhaps I will make the Ether evenly distributed among token owners - although this would take insane amounts of gas...

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javoxac608 wrote 06/19/2022 at 09:24 point

We are a professional real estate services company that provides cash for houses in California. We buy houses from all over the Bay Area, including San Francisco, Oakland, and the surrounding areas. We Buy Houses San Francisco is a house buying company that offers cash for your house. We buy houses from all over the Bay Area, including San Francisco, Oakland, and the surrounding areas.

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vuolietchuio wrote 05/11/2022 at 13:17 point

This is very amazing idea you can check Real estate agent john creek and try it by visiting on this link there are so many important information about different cities.

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oabdo.abdoo.1232f wrote 09/23/2021 at 08:20 point

I like your program  idea. I want to test it for my house project Altana. You can see more detail on this website

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paleengeneer wrote 10/01/2020 at 00:21 point

I'm not sure about this blockchain coin at all. How this could be useful in real life? I can't imagine a serious real estate website that uses HOM Coin. You should definitely change your mind, dude.

  Are you sure? yes | no

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