Algorand Blockchain Basics: An Introduction to Participation Keys

If you’re new to the Algorand network, or perhaps to blockchain as a whole, it can be daunting to get a handle on the technology as well as the terminology. To combat this, I’ll be regularly writing overviews and tutorials about Algorand and Proof of Stake networks as a whole.

Now, let’s dive into participation keys.

What Are Algorand Participation Keys?

In Algorand, there are 2 types of nodes: relay nodes and participation nodes. Relay nodes serve as network hubs in Algorand, relaying protocol messages very quickly and efficiently between participation nodes. Participation nodes support the consensus mechanism in Algorand by proposing and validating new blocks. Participation keys live on participation nodes and are used to sign consensus protocol messages.

A participation key in Algorand is distinct and totally separate from a spending key. When you have an account in Algorand there is an associated spending key (or multiple keys in the case of a multi-sig account). The spending key is needed to spend funds in the account. A participation key, on the other hand, is associated with an account and is used to bring stake online on the network. Importantly, participation keys cannot be used to spend funds in the associated account, they can only be used for helping to support the consensus protocol.

Participation Keys Are Good

Having distinct keys for spending the Algo in an account, and staking the Algo in an account, results in several key security improvements.

In any crypto network, protecting the spending keys is of the utmost importance. Situations that require having spending keys on an internet connected computer are inherently dangerous and always contain the risk of loss of funds.

In Algorand, the spending key never has to be online. The spending key can be kept on an airgapped computer or other offline setup and only used for signing transactions offline. The participation key, in contrast, lives on the participation node and signs protocol messages, but the participation key cannot spend any funds in the account.

This separation of duties in 2 different keys improves the security of Algorand infrastructure substantially. Spending keys can always be kept totally offline and an attacker, if they are able to compromise an internet connected participation node, cannot spend or steal any of the funds in the associated account.

Of course, this doesn’t mean that participation keys shouldn’t be highly protected and secured. If an attacker does compromise a participation key, they can stand up a second participation node with the same participation key. This will result in protocol messages being double-signed, which the network will see as malicious behavior and will treat the node / associated stake as offline.

There is no bonding or slashing in Algorand, and staking rewards are still coming in the future, but regardless: being forced offline due to double signing is undesirable and means that the stake in question will no longer be supporting the consensus mechanism.

Participation Key Mechanics

My examples assume Algorand Node v1 software is installed and running in a participation node configuration on the Algorand MainNet. The software is installed using the Debian package on Ubuntu 18.04, with a standard non-multi-sig Algorand account with some Algo in it, and a separate offline computer with the spending key for the account.

To create a participation key you will need to use the “goal addpartkey” command and specify the account that you want to create the part key for and a validity range:

goal account addpartkey -a WHNXGKYOVIQADYS4VTYBG6SGWFIG6235C5LMXM76J3LHE475QJLIHUC5KY --roundFirstValid 789014 --roundLastValid 4283414

A few things to note. The account specified in the -a flag in the command above (WHNXGKYOVIQADYS4VTYBG6SGWFIG6235C5LMXM76J3LHE475QJLIHUC5KY) is made up and you would need to replace it with your account. Do not use this account as it, and the associated spending key, are not real. Any funds sent to this address will be permanently lost.

The validity range is specified in rounds. Rounds are equivalent to blocks in Algorand. So if you, for example, want to have a key that is valid from now until a point in the future, you need to find the current block height for the roundFirstValid and a future block height for the roundLastValid flag corresponding to the validity range you want.

To find the current block height you can use the “goal node status” command:

derek@algo-node:~$ goal node status Last committed block: 789014 Time since last block: 2.4s Sync Time: 0.0s Last consensus protocol: https://github.com/algorandfoundation/specs/tree/5615adc36bad610c7f165fa2967f4ecfa75125f0 Next consensus protocol: https://github.com/algorandfoundation/specs/tree/5615adc36bad610c7f165fa2967f4ecfa75125f0 Round for next consensus protocol: 789015 Next consensus protocol supported: true Genesis ID: mainnet-v1.0 Genesis hash: wGHE2Pwdvd7S12BL5FaOP20EGYesN73ktiC1qzkkit8=

The last committed block, which is the same as the current block height, is reported as 789014, so we use that for our roundFirstValid. Figuring out the right value for the roundLastValid is a little more involved.

First, you have to determine what time range you want. It is a good practice to rotate participation keys and not to create a key with a really long validity range. In our example, we will use a time range of 6 months. What round corresponds to 6 months from now?

To figure that out, we have to do a little math. 6 months is approximately 182 days. So 182 days x 24 hours / day x 60 min / day x 60 sec / min = 15724800 seconds. At the time of writing, each round in Algorand takes about 4.5 sec. So 15724800 seconds / 4.5 seconds per block = 3494400 blocks. Now we need to add 3494400 to the current block height to get the height 6 months from now. E.g. 3494400 + 789014 = 4283414. This is where the 4283414 in the command above comes from for the roundLastValid.

As the network grows, the 4.5 second block time may not be a safe assumption. This may make the validity range slightly different than 6 months. You need to monitor for key validity and make sure to put a new key in place before the old one expires.

Once the addpartkey command has executed, you can find the participation key at:

/var/lib/algorand/mainnet-v1.0/WHNXGKYOVIQADYS4VTYBG6SGWFIG6235C5LMXM76J3LHE475QJLA.789014.4283414.partkey

It’s beyond the scope of this article, but this file is actually a sqlite database with N number of keys in it which will be internally rotated through automatically during the validity window. This is an additional security measure that is part of Algorand, where the keys used to sign protocol messages are rotated as rounds progress.

With the participation key created, the next step is to bring the account online. An account being online in Algorand means that the Algo in the account is supporting the consensus mechanism. We bring an account online by using the “goal account changeonlinestatus” command. Note that this action requires that you have a small amount of Algo in the account to pay for the transaction. If you have the spending key for the account directly on the participation node you can simply run this command

goal account changeonlinestatus -a WHNXGKYOVIQADYS4VTYBG6SGWFIG6235C5LMXM76J3LHE475QJLA -o=1

However, having the spending key on the participation node is not recommended and kind of defeats the whole purpose of having participation keys in the first place. It is much better to have an airgapped and totally offline computer that has the spending key on it. The process is a little more involved with this setup, but it is much more secure. With this setup you would issue the following command instead:

goal account changeonlinestatus -a WHNXGKYOVIQADYS4VTYBG6SGWFIG6235C5LMXM76J3LHE475QJLA -o=1 -t online.tx

This will produce a transaction file called online.tx in the current directory which has an unsigned transaction to bring the account online. This transaction file then needs to be securely moved to the airgapped computer with the spending key on it. Once on the airgapped computer you can use the algokey utility to sign the transaction file. The command would be:

algokey sign -k spendingkeyfile -t online.tx -o online.tx.signed

Note that algokey is standalone and does not need a running Algorand node. Also, the spendingkeyfile is the file that has the spending key for the account. This file can be created by algokey when you first set up your account.

There is also an option to specify the spending key mnemonic instead of a file, but I find this option worse as it leaves the mnemonic in the shell history, etc. The result of this command is that online.tx.signed will be created in the current directory. This file contains the signed online transaction and it needs to be securely moved back to the running participation node.

Once you have online.tx.signed back on the participation node you can send it to the network with the following command:

goal clerk rawsend -f online.tx.signed

Wait a little bit for the transaction to be processed, and your account should now be online. The creation of a transaction file, movement to the airgapped machine to sign the transaction, movement of the signed transaction back to the online node, and then sending the signed transaction to the network is a general pattern for sending transactions in Algorand without ever putting your spending key online.

Final Thoughts

The design of Algorand using separate keys for spending funds and for participating in network consensus improves the security of nodes running on the Algorand network substantially by protecting spending keys and removing the need for them to ever be online. I think this was a good design choice and wouldn’t be surprised if other protocols adopt this approach.

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Originally published at https://www.purestake.com on July 25, 2019.