Crypto Wallets: Hot and Cold

A crypto wallet is an app or device that holds the keys to your coins and lets you send and receive transactions. One point is worth understanding right away: the coins are not actually stored inside the wallet. They are recorded on the blockchain. What the wallet stores are the keys that prove you have the right to move them.

Keys and addresses

Every wallet is built around a pair of linked keys:

Private key. A secret used to sign transactions. Whoever knows the private key effectively controls the coins.
Public key. Derived from the private key. It is used to produce an address, a string you can safely share so others can send you funds.

Working backward from an address to a private key is practically impossible, so addresses can be shared openly. The private key, and the seed phrase it can be restored from, should never be seen by anyone else.

Most modern wallets generate keys from a seed phrase, a list of 12 or 24 words. It acts as a backup: if your device is lost or broken, you can restore access to your funds in another wallet using that phrase.

Hot wallets

A hot wallet keeps its keys on a device connected to the internet. Common examples include:

mobile wallet apps
browser extensions
desktop programs

The advantage is convenience. Sending a transaction takes moments, and connecting to decentralized applications is easy.

The downside is that the device is always online, which makes it more exposed to malware, phishing and hacking. Many people use hot wallets for smaller amounts and everyday activity.

Cold wallets

A cold wallet keeps keys in an environment that is not connected to the internet. The most common type is a hardware wallet: a small physical device that generates and stores keys internally. Transactions are signed on the device itself, so the private key never leaves it.

The advantage is much stronger protection against remote attacks. Even if your computer is infected, an attacker has a hard time getting the key.

The downsides are less convenience and the need to buy and look after a device. Most importantly, the protection only works if the seed phrase is also stored safely.

Paper wallets, which are simply printed keys, are another form of cold storage. Today they are generally seen as outdated: paper is easy to lose or damage, and the key still has to be entered into software when you want to use it.

Custodial and non-custodial wallets

Another important distinction is who holds the keys.

Custodial wallet. A service, such as a centralized exchange, holds the keys for you. You log in with a username and password, and the service manages the keys on your behalf. It is similar to a bank account: convenient, but you depend on the company's reliability and rules.
Non-custodial wallet. Only you hold the keys. Nobody can freeze or lose your funds for you, but nobody can recover them for you either if you lose your seed phrase.

A common saying in crypto is "not your keys, not your coins". It is a reminder that custodial storage means trusting a third party with your funds.

Safety basics

Never share your seed phrase or private key. Real support staff, wallet developers and exchanges will never ask for them.
Do not store your seed phrase as a photo, screenshot or cloud note. Writing it on paper or stamping it on a metal plate and keeping it somewhere secure is far safer.
Download wallets only from official sources. Scammers build fake apps and websites that look identical to real ones.
Buy hardware wallets from the manufacturer or authorized resellers. A device from an unknown seller could have been tampered with.
Double-check addresses before sending. Some malware silently swaps a copied address for the attacker's.
Send a small test amount first when transferring to a new address for the first time.
Be careful when connecting to websites and signing requests. Do not sign anything you do not understand.

Key takeaways

A wallet stores keys, not coins.
Hot wallets are more convenient; cold wallets are better protected against remote attacks.
With a custodial wallet a service controls the keys; with a non-custodial wallet only you do.
The seed phrase is the master secret: whoever has it controls the funds.