A crypto wallet does not hold coins. It holds the keys that prove you control coins recorded on a blockchain. This article explains private keys, addresses and seed phrases, the types of wallets, and the mistakes that cost people money.
Basic background on how the chain records ownership is in what is a blockchain.
Private key, public key and address
Three related things make up your identity on a blockchain.
- Private key. A very large secret number. Whoever has it can move the funds. It must stay secret.
- Public key. Calculated from the private key. It can be shared safely, and you cannot work backward from it to the private key.
- Address. A shorter form derived from the public key. This is what you give to others to receive funds. It is like an account number that anyone can look up on a block explorer.
A simple comparison: the address is your mailbox, which anyone can drop letters into. The private key is the only key that opens it.
Sending funds means signing a transaction with your private key. The network checks the signature and does not need to know the key itself.
The seed phrase
Private keys are long and hard to write down. So most wallets create a seed phrase, also called a recovery phrase. It is a list of 12 or 24 ordinary words. The wallet uses it to generate your private keys, and the same words always generate the same keys.
That means two things:
- If you lose your device, you can restore everything on a new one by entering the words.
- Anyone who learns the words can take everything. There is no password reset and no support desk that can reverse it.
Never share your seed phrase. No real wallet, exchange, support person or website will ask you to type it in to "verify", "sync" or "claim" something. Anyone who asks is trying to steal from you.
Good habits: write the words on paper, store them offline in a safe place, never photograph them, never save them in a cloud note, email or chat.
Custodial vs self-custodial wallets
Custodial. A company holds the keys for you, as with an account at an exchange. You log in with a password. It is easy to use and recovery is possible, but you depend on the company. If it fails, freezes your account or is hacked, you may not be able to get your funds.
Self-custodial. You hold the keys, usually in an app or browser extension. Nobody can freeze your funds, and you can use any app on the network. You are also fully responsible: a lost seed phrase cannot be recovered.
A common phrase is "not your keys, not your coins". It is a reminder of the trade-off, not a judgment. Many people use both, with a custodial account for convenience and a self-custodial wallet for what they want to control.
Hardware wallets
A hardware wallet is a small device that stores your private keys and signs transactions inside it. The keys never leave the device, even when you connect it to a computer that has a virus. You confirm each transaction on the device's own screen.
This is considered one of the safest ways to hold larger amounts. Buy only from the maker or an authorized reseller, and never use a device that arrives with a pre-written seed phrase.
One address on many chains
Ethereum, Arbitrum, Base, Optimism and Polygon all use the same account design as Ethereum, called EVM. An EVM address looks like 0x followed by 40 hexadecimal characters. The same private key gives you the same address on every one of these chains.
So if your address is 0xABC... on Ethereum, it is also yours on Base and Arbitrum. However, balances are separate. Your ETH on Ethereum is not the same as ETH on Base. Each chain keeps its own ledger, and you move funds between them with a bridge. See bridges and their risks.
Bitcoin and Solana are different. They use other address formats and other cryptography. A Bitcoin address usually starts with 1, 3 or bc1. A Solana address is a string of letters and numbers, typically 32 to 44 characters long, with no 0x. Your wallet creates separate addresses for them from the same seed phrase, or you may use a different wallet.
Sending to the wrong network
A common beginner mistake is choosing the wrong network when sending. Examples:
- Sending USDC on Base to a friend who expects Ethereum. The funds arrive at the same address, but on Base. They are not lost if it is an address the friend controls, but the friend must switch to Base to see them.
- Sending to an exchange deposit address on a network the exchange does not support. Funds may be hard or impossible to recover.
- Sending Bitcoin to an
0xaddress, or EVM tokens to a Bitcoin address. Wallets normally stop this, but not always when pasting manually.
Before you send, check the chain, the address and the token. Send a small test amount first when the sum is large. The cheapest way to send USDC guide shows how the chain choice affects the cost.
Approvals and allowances
On EVM chains, to use a token in an app, you often sign an approval (also called an allowance). It lets a smart contract spend a set amount of your token. Some apps ask for an unlimited approval so you do not have to approve again.
That convenience has a risk. If the app's contract is later hacked or was malicious, it can use the approval to take your tokens. Habits that help:
- Approve only the amount you need when the wallet allows it.
- Review approvals now and then and revoke ones you no longer use.
- Read what a wallet prompt says before you sign. Be careful with prompts that request approval for all your tokens.
You can look at any address's activity on the chain pages using the header search.
Quick safety checklist
- Write the seed phrase offline, and tell nobody.
- Check the first and last characters of an address before sending.
- Confirm the network matches the receiver's.
- Send a small test first for big amounts.
- Be suspicious of urgent messages, free-money offers and requests to connect your wallet.
Frequently asked questions
What is the difference between a private key and a seed phrase?
A private key controls one address. A seed phrase is a list of words that can generate many private keys. The seed phrase is the master backup, so protect it more than anything else.
Can I use the same wallet address on Ethereum and Base?
Yes. Ethereum, Arbitrum, Base, Optimism and Polygon all use the same EVM address format, so one address works on all of them. Balances are separate on each chain.
Is my crypto safe in a wallet app?
Funds in a self-custodial wallet are as safe as your device and your seed phrase are. Keep the phrase offline, update the app, and consider a hardware wallet for larger amounts.
What happens if I lose my seed phrase?
If you still have access to the wallet, move funds to a new wallet with a new seed phrase right away. If you lose both the device and the phrase, nobody can restore access, including the wallet maker.
What should I do if I sent crypto to the wrong network?
First check on a block explorer where the transaction went. If the address is yours on a chain with the same address format, switch your wallet to that chain. If it went to someone else's address or an exchange, contact the receiver or the exchange support, and expect that recovery may not be possible.