Electrum

screenshot of Electrum with its Qt gui

Electrum is a lightweight Bitcoin client, based on a client-server protocol. It was released on november 5, 2011.

Main features:

• Encrypted wallet: the file that contains your bitcoins is protected with a password. You are protected from thieves.
• Deterministic key generation: If you lose your wallet, you can recover it from its seed. You are protected from your own mistakes.
• Instant on: the client does not download the blockchain, it requests that information from a server. No delays, always up-to-date.
• Transactions are signed locally: Your private keys are not shared with the server. You do not have to trust the server with your money.
• Freedom and Privacy: The server does not store user accounts. You are not tied to a particular server, and the server does not need to know you.
• No scripts: Electrum does not download any script. A compromised server cannot send you arbitrary code and steal your bitcoins.
• No single point of failure: The server code is open source, anyone can run a server.
• Firewall friendly: The client does not need to open a port, it simply polls the server for updates.
• Free software: Gnu GPL v3. Anyone can audit the code.
• Written in Python. The code is short, and easy to review.
• Support for Bitcoin URIs, signed URIs and Bitcoin aliases

Graphical User Interfaces

Electrum has two GUIs: one that is based on Gtk, and a newer one based on Qt. The Qt GUI is enabled by default. To use the gtk interface, type:

$ ./electrum -g gtk

In addition, Electrum has a rich set of commands for the command line interface.

Brain Wallet

Electrum uses a type 2 deterministic key generation algorithm. This means that all the keys are derived from a seed.

Typical seeds have 128 bits of entropy. Electrum provides mnemonic code in order to represent the seed.

Example:

• hexadecimal: 431a62f1c86555d3c45e5c4d9e10c8c7
• mnemonic: "constant forest adore false green weave stop guy fur freeze giggle clock"

You can display the seed with the command line interface. Example:

$ ./electrum seed
Password:
431a62f1c86555d3c45e5c4d9e10c8c7 "constant forest adore false green weave stop guy fur freeze giggle clock"

Multiple wallets

Electrum uses one single file per wallet. Your default wallet is located in your user account. If you want to use another wallet, use the -w option followed by the wallet path and name:

$ ./electrum -w /path/to/my/wallet/wallet_name

Export and import addresses

You can export your private keys using the 'addresses' command:

$ ./electrum addresses -ak
Password:
1LGoehbyeX4QBEPK1a6dhyaoMQZfqg5LKX:5JBSttEGhjEcPidSovW66Rin2EZ6LEHZ2qx8Pu2RqqNaDTBVWaF   
1KcsBJa2cCxVkGJfSsg5bUeXN7Y5uLa8mP:5KiP4uiNT6KG8jnXbainCM8rDWRrgxt3PAyut4FFpDoCo1Rh6VM   
1PXsn7LVXTccGhJPTUL8r2EGB4fF9kvex3:5Kj8mvBJReyk8xEBMx5cTnciQCxto5JmudiTPkqwMcd61Kf1Jqc   
1KteSFTAphyByLTtUfFiVQ9s7fMVmx7c2h:5JeZ3FTbWcksLt3PKydd5U9p952UQRHwv3LoxzCA9LZ7V2bku5p   
1GE5ZChAobeTEPLHDCDDKTSg3XvLkcQFjS:5JwtGEygTwF2nouhRVzW3w5DWZd1sCgxLtnd1v51wjkbUrp5sqH   
12YNehfAoYTiwjTXULwaZqTCauu2D61fq6:5Jvcq19ePCXKcVun4n7US99CsrEByUK2kgxXBA3rBVBqYZjhfwD  [change] 

There are two options in this example:

• option -a means: 'list all addresses'. if you don't use it, change addresses are not listed.
• option -k means: display the private keys

You can also import addresses into an electrum wallet, with the 'import' command:

$ ./electrum import 1LGoehbyeX4QBEPK1a6dhyaoMQZfqg5LKX:5JBSttEGhjEcPidSovW66Rin2EZ6LEHZ2qx8Pu2RqqNaDTBVWaF
keypair imported

Note that imported keys do not belong to the deterministic sequence of your wallet; if you import keys in a wallet, you must back it up!

Offline wallet

It is possible to create a transaction on an offline computer, and to broadcast them from another computer, with a wallet that does not have the seed or private keys.

How to prepare an offline wallet

• step 1: create a wallet on your offline computer

$ ./electrum -w wallet create

• step 2: save the seed of your wallet to a file that will remain on the offline computer:

$ ./electrum -w wallet seed | awk '{print $1}'> seedfile

• step 3: blank the seed in your wallet file.

$ electrum deseed 

• step 4: transfer the wallet without seed to the online computer.

For example, copy the wallet file to a usb stick:

$ cp wallet /my/usb/wallet.no_seed

and once you have plugged the usb key to the online computer:

$ cp /my/usb/wallet.no_seed ./wallet.no_seed

• step 5: run electrum on the online computer; this will synchronize your wallet with the bitcoin network, and you will be able to monitor incoming transactions:

./electrum -w wallet.no_seed

How to send a transaction with an offline wallet

• step 1: copy the synchronized wallet file to your offline computer

$ cp wallet.no_seed /usb/stick/wallet.no_seed

• step 2: edit the wallet file and restore the seed :

$ cat wallet.noseed | sed "s/seed:''/seed:'`cat seedfile`'/g" > wallet.seed

you may also do this manually with a file editor if you do not know how to use sed.

• step 3: create the transaction

./electrum -w wallet.seed mktx <recipient> <amount>  >  tx_file

• step 4: with the usb stick, copy the transaction to the online computer:

$cp tx_file /usb/tx_file

and, on the online computer:

$cp /usb/tx_file tx_file

• step 5: broadcast the transaction:

./electrum sendtx  `cat tx_file`

List of commands

command	description	syntax	requires password	needs to be online
help	display the help for a command	help [command]	no	no
validateaddress	check is the argument is a valid bitcoin address	validateaddress <address>	no	no
balance	shows the balance of your wallet or of an address	balance [address]	no	yes
contacts	print your list of contacts	contacts	no	no
create	create a new wallet	create	no	no
restore	restore a wallet from seed	restore	no	yes
payto	create and broadcast a transaction	payto [-s sourceaddr] [-c changeaddr] [-f fee] <address> <amount>	yes	yes
mktx	create a transaction and dump it	mktx [-s sourceaddr] [-c changeaddr] [-f fee] <address> <amount>	yes	no
sendtx	broadcast a transaction	sendtx <tx>	no	yes
password	update your password	password	yes	no
addresses	show your list of addresses, optionally with private keys.	addresses [-a] [-b] [-k]	iff -k	no
history	print the transaction history	history	no	yes
label	change the label of a transaction or address	label <label>	no	no
seed	print your seed	seed	yes	no
import	import a keypair	import <address:private_key>	yes	no
signmessage	sign a message (as in bitcoind)	signmessage <address> <message>	yes	no
verifymessage	verify a message (as in bitcoind)	verifymessage <address> <signature> <message>	no	no
eval	call python eval	eval <expression>	no	no

History

Electrum was announced November 5, 2011.

See Also

• Thin Client Security

External Links

• Electrum project website
• Electrum project source (gitorius)