Public Keys vs Private Keys: What’s the Difference?

Every crypto wallet works with a pair of keys. The private key proves that you own your coins, and the public key lets everyone else check that proof. Knowing the difference tells you what you can safely share and what you must protect. New to wallets? Start with our guide to what a crypto wallet is and how it works.

This matters as soon as you own crypto. Crypto is delivered to the wallet address you provide, so when you buy crypto on Coinmama, the private key behind that address decides who can move the coins.

What is the difference between a public key and a private key?

A private key signs transactions and must stay secret. A public key verifies those signatures and can be seen by anyone. The two are made as a pair: the public key is calculated from the private key, but the private key cannot be worked out from the public key.

Both come from public-key cryptography, the maths behind digital signatures. Our guide to what cryptography is covers the basics. Here is how the two keys compare:

What is a private key?

A private key is a secret number that controls the crypto at an address. In Bitcoin it is a 256-bit number, picked at random from about 10⁷⁷ possible values. An Ethereum private key is usually shown as 64 hexadecimal characters (the digits 0 to 9 and the letters a to f).

Your wallet uses the private key to sign transactions. The signature is the network’s proof that the owner approved the payment. Whoever holds the key can make that proof, so whoever holds the key controls the coins.

The U.S. Securities and Exchange Commission (SEC) compares a private key to a password for your wallet, with one big difference: once created, it cannot be changed or replaced. If you lose it and have no backup, you lose access to the crypto for good. Our guide on what happens if you lose your private keys explains your options.

Most wallets manage private keys for you and show you a seed phrase instead, as explained below.

What is a public key?

A public key is a number calculated from your private key that lets anyone check your signatures. It cannot sign anything itself. The SEC notes that a public key does not give access to the private key and cannot be used to authorize transactions.

The calculation only runs one way. Bitcoin and Ethereum both use elliptic curve cryptography (Bitcoin’s curve is called secp256k1). Going from the private key to the public key is quick. Going back from the public key to the private key is not feasible, so anyone can verify your payments without learning the secret that controls them.

What is a wallet address?

A wallet address is the code you share so people can send you crypto. A crypto address is usually made by hashing the public key (running it through a one-way function that produces a shorter fingerprint) and adding a checksum that catches typing errors.

Bitcoin has several address types. You can tell them apart by their first characters:

• 1… Legacy (P2PKH): a hash of a public key.
• 3… Script (P2SH): a hash of a script, used for example by multi-signature wallets.
• bc1q… Native SegWit (Bech32): a hash of a public key or script in a newer format that is better at catching typos.
• bc1p… Taproot (Bech32m): holds a public key directly, usually a modified (tweaked) one, instead of a hash.

Ethereum works differently. An Ethereum address is 0x followed by 40 hexadecimal characters: the last 20 bytes of a Keccak-256 hash of the public key. Some addresses mix capital and small letters as a built-in typo check, as our guide to whether Ethereum addresses are case-sensitive explains.

An address can receive funds but cannot approve spending. Each blockchain has its own format, so check that an address matches the coin and network before you send. Our step-by-step guide to sending Bitcoin to a wallet shows how.

How do digital signatures work?

A digital signature proves that the owner of a private key approved a transaction, without revealing the key. The private key signs and the public key verifies. Signing does not encrypt or hide the payment: Bitcoin.org points out that all Bitcoin transactions are public, traceable and permanently stored.

Here is the whole chain, from a new key to a confirmed payment:

Wallets normally sign the whole transaction, including amounts and recipients. Change those details and the signature no longer verifies, so it cannot be reused to send your coins elsewhere. Bitcoin uses ECDSA signatures; Taproot uses Schnorr signatures. Once confirmed, a payment is final: blockchain transactions cannot be reversed.

What is the difference between a seed phrase and a private key?

A private key controls the coins at one address, while a seed phrase is a master backup that can rebuild all the private keys in a wallet. Most modern wallets show you a seed phrase when you set them up, not individual keys.

Two Bitcoin standards explain how this works. BIP 39 turns 128 to 256 bits of random data into 12 to 24 words from a fixed list of 2,048. BIP 32 then derives a whole tree of key pairs from the seed those words encode. That is why one backup can cover many addresses, and why a wallet can create new receiving addresses without exposing any private key.

The practical difference is scope. Someone who steals one private key can take the coins that key controls. Someone who steals your seed phrase can take everything in the wallet, including crypto it receives later. Treat the seed phrase as your most sensitive secret.

Some wallets add an optional passphrase. The same words with a different passphrase open a different wallet, so record both.

How do I keep my private key safe?

Keep your private key and seed phrase offline, private and backed up, and never type them into a website or share them with anyone. The SEC’s advice is simple: never share your private keys or seed phrases.

• Get wallet software from the source. Download it only from the maker’s official website or its official store listing.
• Write the seed phrase on paper. No screenshots, photos, cloud notes or emails: Bitcoin.org warns that any backup stored online is highly vulnerable to theft. Keep copies in more than one safe place.
• Keep your wallet software up to date. Updates bring security fixes.
• Match storage to the amount. Bitcoin.org suggests keeping only small amounts on your phone or computer for everyday use. For larger sums, compare a hot wallet vs a cold wallet.
• Ignore anyone who asks for your keys. Nobody needs your private key or seed phrase to send you crypto. Learn to spot phishing attacks and people pretending to be Coinmama staff.

Malcolm O'Mahony

Malcolm is a Content Marketing Manager at Coinmama. He's passionate about Web3 and specializes in making complex concepts easy to understand. Crypto since 2017. Coinmama since 2020.

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