This is a small example cryptocurrency which is based on Bitcoin. It was written for my bachelor thesis Implementierung einer eigenen Kryptowährung in Java nach dem Vorbild Bitcoin which roughly translates to implementation of an own java based cryptocurrency in the manner of Bitcoin. It features the blockchain technology and a simple input-output-system. Please refer to the Wiki pages if you are interested in a more detailed explanation.

Democoin has an own docker image.

docker run -d \
--publish=7777:7777 \
-v /Users/theo/desktop/democoin/data:/data \
-v /Users/theo/desktop/democoin/logs:/logs \
theovier/democoin \
-m "my message" \
-a "1AQPpmmMrUBCCdEJBt7usSrXG7ZTuBs9tu"

This command will start a stand-alone full-node which will automatically try to connect with other nodes who are expected to be online 24/7. This full-node will manage an own blockchain, mine new blocks and listen for incoming connections. The docker independent parameters -m <message> and -a <address> are optional. They allow you to specifiy an address to which the mining reward is sent. Additionally you may define a message for the coinbase transaction. To enable verbose logging, add the parameter -v. The IPs of those nodes are for the moment hardcoded in the NetworkParams.java.

Democoin uses the same base-58 addresses as Bitcoin. To generate new addresses with corresponding private keys either use the provided jar directly or compile the client module yourself.

java -jar address_generator.jar

Generated addresses will always end in .key, for example: 1AVuQjcnquXEaXgggJx7TsyMBjbatiBtNB.key. They can be opened with regular text editors and contain the corresponding private key which was used to generated them. Keep this file private or else someone else can spent your coins.

To create and broadcast transactions, use the spend_tx.jar. You will need to provide inputs, outputs, an optional message and an IP to which the transaction is sent. Keep in mind that transactions can only be validated by full-nodes, which means you can create invalid transactions but those are going to be rejected by honest full-node.

java -jar spend_tx.jar \
-in 6b62ca894aecb4474a34828ba2b7f690acae6cb2755c3beb238287eee117f23e 0 ./1AVuQjcnquXEaXgggJx7TsyMBjbatiBtNB.key \
-out 13bxQW7poaa5pC3h7NttviQ1kUBwJa7qvY 50 \
-msg "my transaction" \
-host 192.168.0.144

To reference an unspent transaction output (UTXO) from a previous transaction as an input, you need to provide the following -in <transactionID> <outputIndex> <path to the corresponding private key file>. To specify an output, you'll need to define a target address and the amount you want to spent -out <targetAddress> <amount>. You may include as many inputs and outputs as you like; there is no limit.

If you don't want to wait for new releases you can compile the source code yourself. As this is a maven project you need to make sure to have the java build management tool maven3 installed. To check your maven version type

mvn -v

it should display something along this lines

Apache Maven 3.5.0 (ff8f5e7444045639af65f6095c62210b5713f426; 2017-04-03T21:39:06+02:00)

If you installed maven just clone the repository or download the .zip and navigate to the pom.xml. Then simply run

mvn package

and check your /target folder for the newly generated jar file.

Theo Harkenbusch @theovier