UbuntuHak: Bitcoin Basics and Ubuntu 12.04

Linux, Bitcoin client

Bitcoin Exchanges / November 29, 2015

Electrum’s focus is speed, with low resource usage and simplifying Bitcoin. Startup times are instant because it operates in conjunction with high-performance servers that handle the most complicated parts of the Bitcoin system.

Does Electrum trust servers?

Not really; the Electrum client never sends private keys to the servers. In addition, it verifies the information reported by servers, using a technique called Simple Payment Verification

What is the Seed?

The seed is a random phrase that is used to generate your private keys.


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Your wallet can be entirely recovered from its seed. For this, select the “restore wallet” option in the startup.

How secure is the seed?

The seed phrase created by Electrum has 132 bits of entropy. This means that it provides the same level of security as a Bitcoin private key (of length 256 bits). Indeed, an elliptic curve key of length n provides n/2 bits of security.

I have forgotten my password. What can I do?

It is not possible to recover your password. However, you can restore restore your wallet from its seed phrase, and and choose a new password. If you lose both your password and your seed, there is not way to recover your money. This is why we ask you to save your seed phrase on paper.

My transaction has been unconfirmed for a long time. What can I do?

Bitcoin transactions become ‘confirmed’ when miners accept to write them in the Bitcoin blockchain. In general, the speed of confirmation depends on the fee you attach to your transaction; miners prioritize transaction that pay the highest fees.

Recent versions of Electrum use ‘dynamic fees’, in order to make sure that the fee you pay with your transaction is adequate. This feature is enabled by default in recent versions of Electrum.

If you have made a transaction that is unconfirmed, you can:

  • Wait for a long time. Eventually, your transaction will either be confirmed or cancelled. This might take several days.
  • Increase the transaction fee. This is only possible for ‘replaceable’ transactions. To create this type of transaction, you must have enabled ‘Replace by Fee’ in your preferences, before sending the transaction.
  • Create a ‘Child Pays For Parent’ transaction. A CPFP is a new transaction, that pays a high fee in order to compensate for the small fee of its parent transaction. It can be done by the recipient of the funds, or by the sender, if the transaction has a change output.

What does it mean to “Freeze” an address in Electrum?

When you freeze an address, the funds in that address will not be used for sending bitcoins. You can not send Bitcoins if you don’t have enough funds in the non-frozen addresses.

How is the wallet encrypted?

Electrum uses two separate levels of encryption:

  • Your seed and private keys are encrypted using AES-256-CBC. The private keys are decrypted only briefly, when you need to sign a transaction; for this you need to enter your password. This is done in order to minimize the amount of time during which sensitive information is unencrypted in your computer’s memory.
  • In addition, your wallet file may be encrypted on disk. Note that the wallet information will remain unencrypted in the memory of your computer for the duration of your session. If a wallet is encrypted, then its password will be required in order to open it. Note that the password will not be kept in memory; Electrum does not need it in order to save the wallet on disk, because it uses asymmetric encryption (ECIES).

Wallet file encryption is activated by default since version 2.8. It is intended to protect your privacy, but also to prevent you from requesting bitcoins on a wallet that you do not control.

Can I import private keys from other Bitcoin clients?

In Electrum 2.0, you cannot import private keys in a wallet that has a seed. You should sweep them instead.

If you want to import private keys and not sweep them you need to create a special wallet that does not have a seed. For this, create a new wallet, select “restore”, and instead of typing your seed, type a list of private keys, or a list of addresses if you want to create a watching-only wallet.

You will need to back up this wallet, because it cannot be recovered from seed.

Can I sweep private keys from other Bitcoin clients?

Sweeping private keys means to send all the bitcoins they control to an existing address in your wallet. The private keys you sweep do not become a part of your wallet. Instead, all the bitcoins they control are sent to an address that has been deterministically generated from your wallet seed.

To sweep private keys go to Wallet menu -> Private Keys -> Sweep. Enter the private keys in the appropriate field. Leave the ‘Address’ field unchanged. That is the destination address and it’ll be from your existing electrum wallet.

Where is my wallet file located?

The default wallet file is called default_wallet which is created when you first run the application and located under the /wallets folder.

On Windows:

  • Show hidden files
  • Go to UsersYourUserNameAppDataRoamingElectrumwallets

On Mac:

  • Open Finder
  • Go to folder (shift+cmd+G) and type ~/.electrum

On Linux:

  • Home Folder
  • Go -> Location and type ~/.electrum

Can I do bulk payments with Electrum?

You can create a transaction with several outputs. In the GUI, type each address and amount on a line, separated by a comma.

Amounts are in the current unit set in the client. The total is shown in the GUI.

You can also import a CSV file in the ‘Pay to’ field, by clicking on the folder icon.

Can Electrum create and sign raw transactions?

Electrum lets you create and sign raw transactions right from the user interface using a form.

Electrum freezes when I try to send bitcoins

This might happen if you are trying to spend a large number of transactions outputs (for example, if you have collected hundreds of donations from a Bitcoin faucet). When you send Bitcoins, Electrum looks for unspent coins that are in your wallet, in order to create a new transaction. Unspent coins can have different values, much like physical coins and bills.

If this happens, you should consolidate your transaction inputs, by sending smaller amounts of bitcoins to one of your wallet addresses; this would be the equivalent of exchanging a stack of nickels for a dollar bill.

Source: docs.electrum.org