Day 2: Wallets, keys and seed phrases
Owning crypto means controlling keys. Today: what a wallet really stores and how people lose coins. About 5 minutes.
1. Crypto wallet
A crypto wallet is software or hardware that stores the keys controlling your coins and lets you send and receive them. Despite the name, a wallet does not hold the coins themselves; those exist only as entries on the blockchain. The wallet holds the private keys that prove you may move them. Wallets come in several forms: mobile and desktop apps, browser extensions, and dedicated hardware devices. They can be custodial, where a company such as an exchange holds the keys for you, or non-custodial, where only you hold them, usually backed up by a seed phrase. Every wallet involves a trade-off between convenience and security. A useful rule is to keep small spending amounts in an app and larger savings in a hardware wallet, with the seed phrase backed up offline.
In India: Coins left on an Indian exchange are in a custodial wallet controlled by that exchange. Withdrawing to your own wallet is legal; keep records of transfers for tax purposes.
More on Crypto wallet →2. Private key
A private key is a secret number that gives control over coins at a blockchain address. With it, your wallet creates digital signatures that prove you authorise a transaction, without revealing the key itself. For Bitcoin and Ethereum it is a 256-bit number, which is far too large to guess. From the private key, software derives a public key and from that an address you can share for receiving funds. The process only works one way: knowing an address or public key does not reveal the private key. Whoever has the private key controls the funds, and transactions cannot be reversed. If someone else learns your key they can take everything; if you lose it with no backup, the coins are inaccessible forever. Modern wallets derive many keys from a single seed phrase, so protecting that phrase protects all of them.
More on Private key →3. Seed phrase (recovery phrase)
A seed phrase is a list of usually 12 or 24 ordinary words, generated by your wallet, that encodes the master secret from which all your wallet's private keys are derived. Most wallets follow the BIP-39 standard, which uses a fixed list of 2,048 English words. If your phone breaks or your hardware wallet is lost, entering the seed phrase into a compatible wallet restores access to all your funds. That also means anyone who sees the phrase can steal everything. Write it down on paper or stamp it in metal and store it offline somewhere safe. Never type it into a website, share it in a chat, store it in a photo or cloud note, or give it to "support staff". No legitimate wallet, exchange or helpdesk will ever ask for it; a request for your seed phrase is a scam.
More on Seed phrase (recovery phrase) →4. Custodial vs non-custodial wallet
In a custodial wallet, a third party such as an exchange or payment app holds the private keys and you hold an account with them. In a non-custodial (self-custody) wallet, only you hold the keys. Custodial services are convenient: you can reset a forgotten password, trade instantly and get customer support. But your coins are only as safe as the company. If the custodian is hacked, freezes withdrawals or goes bankrupt, you may lose access. When Mt. Gox collapsed in 2014, customers waited about a decade for repayments to begin. FTX customers, after its 2022 collapse, were repaid in dollars at November 2022 prices, so they missed the later recovery in crypto prices. The saying "not your keys, not your coins" comes from these events. Self-custody removes that counterparty risk but makes you fully responsible for backups and security. Many people use both: an exchange for buying and selling, and a self-custody wallet for holding.
In India: Indian exchanges registered with FIU-IND hold customer coins in custody and must follow anti-money-laundering rules. Check an exchange's registration and proof-of-reserves disclosures before depositing.
More on Custodial vs non-custodial wallet →5. Cold wallet (cold storage)
A cold wallet keeps private keys on a device that never exposes them to the internet. The most common type is a hardware wallet: a small dedicated device that stores keys internally and signs transactions on the device, so the keys never touch your computer or phone. Paper wallets and fully offline computers are older forms of cold storage. Cold storage greatly reduces the risk of remote hacking. The remaining risks are physical loss, theft, damage, and mistakes with the seed phrase backup. You should still verify receiving addresses and transaction details on the device's own screen. Buy hardware wallets only from the manufacturer or an authorised seller, as tampered second-hand devices have been used in scams. Set the device up yourself, and never use one that arrives with a pre-printed seed phrase.
More on Cold wallet (cold storage) →
Do this today
Read: how to buy Bitcoin in India →The practical steps, from KYC to withdrawing to your own wallet.
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General information, not financial advice.