Recently there have been a number of proposals for bitcoin clients which do not store a complete copy of every block in the entire block chain. This page will refer to all such clients as "thin clients". This page is meant to be a place to try to make sense of the security and trust implications of the various schemes.

== Block Height vs. Depth ==

It is important to distinguish between block height verification and block depth verification.

A client verifies the height H of a block by checking that there are H block '''before''' it, all of which are well-formed and obey the maximum-difficulty-adjustment-rate rule. Currently only the Satoshi client, libbitcoin, and btcd do block height verification. Block height is the fundamental anchor of trustless security in the Bitcoin system.

A client verifies the depth D of a block by checking that there are D blocks '''after''' it (also called "confirmations"), all of which are well-formed. SPV clients substitute block depth for block height as a transaction validity check. All clients use block depth as a measure of the liklihood of a [[Chain_Reorganization|block chain reorganization]] producing a new longer fork which excludes the transaction (i.e. [[Orphan_Block|orphaning]] its block).

See also [https://bitcointalk.org/index.php?topic=88208.msg987429#msg987429 some comments on probabilistic verification of block height].

== Full-Node Clients ==

The "thick" bitcoin client downloads a copy of the entire chain, including all transactions (not just headers). It will be used as the reference point for security comparisons below.

A full-node client uses the [[Protocol_rules#Blocks well-formed|difficultywise-longest]] valid block chain it can find. A transaction's ''depth'' (the number of blocks ''after'' it) is used to determine the likelihood of the transaction being double-spent due to the emergence of a longer fork.

==== [[bitcoind|bitcoin-qt]] ====

==== [https://github.com/conformal/btcd btcd] ====

== Header-Only Clients ==

These client downloads a complete copy of the headers for all blocks in the entire block chain. This means that the download and storage requirements scale linearly with the amount of time since bitcoin was invented; it would be preferable to have the scaling be logarithmic or even constant.

=== Simplified Payment Verification (SPV) ===

This scheme is described in section 8 of the [http://bitcoin.org/bitcoin.pdf original bitcoin whitepaper].

==== Block '''Depth''' as a Transaction Validity Check ====

As Satoshi writes, "[the thin client] can't check the transaction for himself, but by linking it to a place in the chain, he can see that a network node has accepted it, and blocks added after it further confirm the network has accepted it." If we take "X" to be the "number of blocks added after it", then SPV essentially trusts that a transaction X blocks deep in the chain does not have inputs which were already spent further back in the chain. Therefore, the validity of a transaction is determined by its depth -- i.e. how many blocks come ''after'' it. Other thin client protocols also include this assumption.

This is very different from the trust model in the "thick" client: the thick client verifies that a transaction's inputs are unspent by actually checking the whole chain up to that point -- there is no "X blocks deep" involved here. The thick client uses "X blocks deep" (aka "confirmations") only once it has already decided that a transaction is valid (i.e. no [[Double-spending|double-spends]]). At that point it uses "X blocks deep" to decide how likely it is that a longer fork in the chain will emerge which excludes that transaction.

It is very important to understand how the same property ("X blocks deep") is used to verify two different properties in the thick client and SPV cases. '''The thick client never uses block depth as a measure of transaction validity; the SPV client does'''.

This is a concern in a situation where an SPV client is subjected to a double-spend attack by somebody who controls its network connection. For example, suppose you are at a wi-fi cafe and are paying for something using your smartphone -- the cafe owner controls your network connection. Satoshi acknowledges this implicitly when he writes that "the verification is reliable as long as honest nodes control the network" -- to be completely pedantic, this means that the verification is reliable as long as honest nodes control '''the part of the network that the SPV client is able to communicate with'''. In an attack-by-ISP scenario this may not be a sufficiently strong security property. The attacker would not need to overpower "the rest of the network" because the client is unable to communicate with it.

==== [[BitCoinJ|bitcoinj]] ====

Simplified Payment Verification is the verification mechanism used in [[BitCoinJ|bitcoinj]].

A security analysis of some of the issues in bitcoinj can be found [http://code.google.com/p/bitcoinj/wiki/SecurityModel here]; however:

* The claim that "picking 10 nodes and requiring all of them to be consistent needs much less trust" overlooks the problem of [https://en.bitcoin.it/wiki/Weaknesses#Cancer_nodes "cancer nodes"] and [http://en.wikipedia.org/wiki/Sybil_attack Sybil attacks].
* Many of the security claims are qualified by some form of "if you don't think an attacker controls your internet connection"; see the previous section for a discussion of why this is problematic.

==== [https://bitcointalk.org/index.php?topic=128055.0 picocoin] ====

Simplified Payment Verification is the verification mechanism used in picocoin.

The library (libccoin) that picocoin is based on includes code for validating scripts and blocks; this could potentially be used to implement a full-chain client.

==== [[Electrum]] ====

Electrum fetches blockchain information from Electrum servers, bitcoin nodes that index the blockchain by address.
Electrum performs Simple Payment Verification to check the transactions returned by servers.
For this, it fetches blokchain headers from about 10 random servers.
In addition, Electrum servers are authenticated by SSL, in order to protect users from MITM attacks.

=== Unused Output Tree in the Block chain (UOT) ===

There have been several proposals (the first appears to be [https://bitcointalk.org/index.php?topic=21995.0 this one] by gmaxwell, who called it an "open transaction tree", although the term "open" is now taken to mean "not yet mined into the block chain" rather than "unspent") to form a tree of unused transaction outputs at each block in the chain, hash it as a Merkle tree, and encode the root hash in the block chain (probably as part of the coinbase input). This will be called an Unused Output Tree (UOT). The first detailed proposal so far appears to be [https://en.bitcoin.it/wiki/User:DiThi/MTUT Alberto Torres' proposal]; etotheipi's [https://bitcointalk.org/index.php?topic=88208.0 ultimate block chain compression] is a variant of this.

If such UOT hashes were included in the block chain, a client which shipped with a [https://en.bitcoin.it/wiki/Vocabulary checkpoint] block that had a UOT would only need to download blocks after the checkpoint. Moreover, once the client had downloaded those blocks and confirmed their UOTs, it could discard all but the most recent block containing a UOT.

This would also let a thin client reduce the question of "is this output unspent" to the question of "is this block super-well-formed" where "well-formed" means "well-formed according to the normal block chain rules and additionally has an Unused Output Tree which is accurate and truthful". This is still a long way from the low level of trust involved in the thick client, but it is a major improvement over all existing proposals.

It is unlikely that bitcoin would ever arrive at a state where every single block had a UOT, since this would require upgrading 100% of the miners on the network, or else convincing enough miners to reject blocks which do not contain a UOT. The latter strategy risks creating block chain forks, which can be expensive (in reward terms) to miners. Therefore, any UOT strategy would need to cope with the fact that not every block contains a UOT.

Hostile miners may insert blocks into the chain which have what claims to be a UOT, but which is actually invalid. It is unlikely that such blocks could be kept out of the chain because, again, this would require adding a new block well-formedness criterion, and miners implementing this new criterion would risk "mining on the wrong side" of a fork, which could cost them a lot of money. Therefore, any UOT strategy would need to cope with the fact that not every block containing a UOT entry can be trusted.

Note that at the present moment no standard format for such Unused Output Tree hashes has been agreed upon, nor do any of the blocks in the chain contain them. The [https://bitcointalk.org/index.php?topic=91954 ultraprune] feature added to bitcoind-0.8 maintains a similar data structure on the client's disk. It does not put this data structure or its hash anywhere in the block chain.

== Server-Trusting Clients ==

These clients involve some (usually low) level of trust in the server they rely upon. Mechanisms for authenticating the server, and for confirming that the server has not been compromised, are usually not explained.

All thin clients listed below currently connect to a single server, and are vulnerable to an attack similar to a double-spend. The attack can be run by that single server - the server can just lie to them that they received a Bitcoin transaction, and they, assuming the server does not lie, perform some service, transfer funds or send goods without actually receiving any Bitcoin in exchange. Therefore, they are implicitly trusting it.

Future enhancements have been suggested that will have the client talk to multiple servers and broadcast transactions and query all of them. Unfortunately it is well known to security researchers that this does not actually increase security; it simply makes the exploits more complicated and difficult to find. Security researchers have a name for this phenomenon: it is called a "Sybil attack"<ref>http://en.wikipedia.org/wiki/Sybil_attack</ref>. [https://bitcointalk.org/index.php?topic=88208.msg975201#msg975201 This post] on bitcointalk explains how some governments (notably Iran and China) already perform these sorts of attacks on their own citizens, with the coerced assistance of SSL certificate authorities.

Clients with a checkpoint (even a very old one) that download and validate the headers for the whole block chain are [http://bitcoinmedia.com/the-irc-bootstrap-method-is-flawed/#comment-4243 not vulnerable] to Sybil attacks in the following sense: they can always ensure that an attack would cost more than the amount being stolen.

=== [[BCCAPI]] ===

== Other ==

* A [http://sourceforge.net/mailarchive/message.php?msg_id=28633866 thread] on bitcoin-dev
* A [http://bitcoin.stackexchange.com/questions/2584/is-reclaiming-disk-space-already-implemented-how-effective-will-it-be/2589 question] on bitcoin.stackexchange.com
* The [[Weaknesses#Sybil_attack|sybil attack (also known as "cancer nodes")]] paragraph explains some of the issues with thin clients that base security on trusting whatever "a majority of the IP addresses I can see" say.
* [http://bitcoin.stackexchange.com/questions/2613/how-secure-are-various-models-of-bitcoin-clients related discussion on Stack Exchange]
* A hypothesized [https://bitcointalk.org/index.php?topic=134318.msg1441171#msg1441171 intermediate security class] between SPV and full-chain validation.

<references>

[[Category:Technical]]
[[category:Clients]]
[[Category:Security]]

Electrum

2015-02-04T17:37:01Z

ThomasV:

2012-07-02T09:21:47Z

ThomasV:

== Licensing ==
{{self|Cc-zero}}

Electrum/Translation

2012-06-27T15:23:46Z

ThomasV:

Electrum/Translation

2012-06-27T11:53:17Z

ThomasV: no colons

2012-06-14T08:16:41Z

ThomasV:

Electrum/Documentation

2012-06-14T08:16:32Z

ThomasV: /* What is the "Gap Limit"? */

==Documentation of Electrum Bitcoin Client (Focus on the GUI)==
This page tries to document certain aspects of the [[Electrum|Electrum]] Bitcoin Client. The focus is on explaining certain aspects of its GUI, such that it gets easier for the user to understand its use.

More documentation, especially with regard to command line parameters, can be found at the parent page of this Wiki, i.e. [[Electrum|here]].

===Version Info===
Unless stated otherwise in particular sub-sections, the present state of this documentation is based on
* '''Electrum version 0.58'''
As this documentation gets updated, this "version info" can be updated, too!

Later versions of Electrum may add new features or deviate from this description to some extend.

===Open/Unclear Points===

Discussions about unclear points should take place on the [[Talk:Electrum/Documentation|Discussion page.]]

==What is a "Wallet" and a "Bitcoin Address"?==
* (General, not specific to Electrum)

Your wallet is a list of Bitcoin addresses (more precisely: a list of privat/public key pairs). Each address "contains" (or is associated with) a certain amount of Bitcoins at a given time.

Your wallet's balance is the sum of all Bitcoins of all your wallet's Bitcoin addresses.

Your wallet consists of both [[#Normal Addresses|normal addresses]] and [[#Change Addresses|change addresses]]. Although they are fully equivalent from the Bitcoin protocol's point of view, they are different in how they are used by Bitcoin clients like Electrum.

===Normal Addresses===
* (More or less general, not too specific to Electrum)
====How are New "Normal Addresses" Created for my Wallet?====
A Bitcoin client allows you to trigger the generation of a new Bitcoin address either manually, or it generates new addresses automatically upon certain conditions. The latter applies to Electrum: Depending on the "[[#What is the "Gap Limit"?|gap limit]]" setting in Electrum's program preferences, there will always be a certain number of unused addresses showing up in your list of receive addresses (=your own wallet's addresses), and as these addresses get used, new ones will show up automatically.

Typically you want to use a new address for receiving Bitcoins from somebody, instead of using any of your wallet's present addresses that have already been used for earlier transactions. This is to protect your privacy, because all Bitcoins transfers are published in the blockchain and can be read by anyone.

Another way of adding addresses to your wallet is to [[#Imported Addresses|import]] private keys (with their addresses of course), using Electrum's [[Electrum|command line options]]. See section about [[#Imported Addresses|imported addresses]] for more details.

===Change Addresses===
* (More or less general, not too specific to Electrum)
====What is a "Change Address", and why is it useful?====
The concept of change addresses is a feature not of the Bitcoin protocol, but of a Bitcoin client. It is implemented not only in Electrum but in most Bitcoin clients, including the original "Satoshi" Bitcoin client.

'''How it works:'''

Whenever your Bitcoin client (e.g. Electrum) sends Bitcoins from your wallet's address "A" to a foreing address "B", a new change address "C" is created by Electrum and added to your wallet.

Example: Address "A" has 20 BTC. Electrum sends 9 BTC from "A" to "B". The change (20-9 = 11 BTC) is sent to the "change address" "C". For this purpose, address "C" is created by Electrum at this moment and added to your wallet.

Exception: If all the Bitcoins of "A" are sent to "B", there is no need for creating a change address "C".

Actually, Bitcoin clients can also work without change addresses. In this case, the change would be sent back to "A" instead of the new address "C".

'''Why the concept of "change addresses" is useful:'''

* Using a new change address makes it more difficult for other people (by analyzing the blockchain) to track how many Bitcoins you have or where you're spending them.
* It also conceals which output is the "spend" and which is the "change".

===Imported Addresses===
Instead of generating new addresses in the default way from the wallet's [[#Seed|seed]], Electrum also allows you to import addresses (and their private keys of course) from external sources, e.g. from another Bitcoin client's wallet. For this, use Electrum's [[Electrum|command line]] options. Note that imported addresses cannot be recovered from your wallet's [[#Seed|seed]] and therefore need to be secured separately for a complete backup of your wallet.

Imported addresses can be used like any other [[#Normal Addresses|normal]] receive address with Electrum for transmission or reception of Bitcoins, and can also be (un)tagged as [[#What does it mean to "Prioritize" or "Freeze" Addresses in Electrum?|"prioritized" or "frozen"]].

===Deterministic Wallet===
====What is a "Deterministic Wallet" in Electrum?====
Traditionally, all new addresses (incl. the private keys of course) added to the wallet ([[#Normal Addresses|normal addresses]] or [[#Change Addresses|change addresses]]) are generated randomly. This is the case e.g. for the original "Satoshi Bitcoin Client" (at least as of today, version 0.6.2).

Contrary to that, a Bitcoin client with a "Deterministic Wallet" will generate all new addresses accoding to a pre-defined (i.e. "deterministic") algorithm as a function of a wallet-specific [[#Seed|seed]], which is a 128 bit number. This means, if the seed is known, all new addresses that Electrum will ever create for this wallet are known, because Electrum's algorithm is known (and open source).
This is a big advantage when it comes to making wallet backups:
* ''Traditionally'', a wallet backup just contains the bitcoin addresses (and private keys of course) that have been created by the client by the time the backup was made. If the user performs transactions after the backup, new addresses ([[#Normal Addresses|normal]] or [[#Change Addresses|change]] addresses) will be generated and added to the wallet. These are not included in the backup yet. If the wallet in use gets lost, all the Bitcoins that are associated with the new addresses will also be lost. To avoid the risk of a too high loss, regular wallet backups are important.
* ''With a Deterministic Wallet'' (like with Electrum), the wallet backup only needs to contain the seed, and all new addresses generated in the future are already secured by the initial backup. Hence, regular new backups are not required!

===Seed===
====What is the "Seed" of a Deterministic Wallet in Electrum?====
The Seed of a [[#Deterministic Wallet|deterministic wallet]] is a series of 128 random bits in Electrum.
For convenience, a seed can also be expressed by a sequence of 12 words in Electrum, and it also supports generation of a QR code to facilitate the backup of the seed.

So there are 2^128 possible seeds for a deterministic wallet in Electrum.
For comparison, the total number of Bitcoin addresses is 2^160, and the number of atoms on earth is 2^166.
So there exists one Bitcoin address per 1 Million atoms on earth, and there exists one seed of Electrum wallets per 4.3 Billion Bitcoin addresses.
(By the way: The number of atoms in the complete universe is estimated as 2^266).

===What is the "Gap Limit"?===

The gap limit is the maximal number of contiguous unused addresses in your deterministic sequence of addresses.

If you recover your wallet from seed, you will notice that the gap limit is asked by the recovery dialog.
It is used in order to decide when to stop the recovery procedure.

If you need to have more receiving addresses in your wallet, you may increase your gap limit (expert mode).
This, however, means that you will need to remember the new limit in order to be able to recover your wallet from seed.

==More on the Electrum GUI==
===What does it mean to "Prioritize" or "Freeze" Addresses in Electrum?===
When sending Bitcoins to a foreign address, Electrum will by default use a built-in method to select the address(es) of the wallet used for sending these Bitcoins.

* When you ''prioritize'' some of your wallet's addresses, these addresses will be used with preference. Other addresses will not be used until the prioritized addresses contain no more Bitcoins.
* When you ''freeze'' some of your wallet's addresses, these addresses will not be used for sending bitcoins. Instead, other addresses will be used. Sending Bitcoins is not possible if the non-frozen addresses of your wallet do not contain enough funds.

The user can (de)prioritize or (un)freeze both [[#Normal Addresses|normal]] and [[#Change Addresses|change]] addresses.

Note: Clearly, an address can not be "prioritized" and "frozen" at the same time.

===What does the "Tx" column mean in Electrum?===
* Expert Mode only
* Applies to "Receive" tab (own wallet's addresses) and "Contacts" tab (foreing addresses).

Tx stands for {... ?? "Transaction"? "Transmission" ?? ...}

The Tx column in Electrum displays a number for each Bitcoin address in the address list, both for own addresses ("Receive" tab) and for foreing addresses ("Contacts" tab).

'''In the "Receive" tab (own addresses):'''

The number in the Tx column indicates the total number of _incoming_ Bitcoin transactions that have ever been sent to this address.

{
The number of outgoing transactions is apparently not counted. It is unclear why the column is called "Tx" and not "Rx", because it indicates the number of times that Bitcoins have been sent to this address, i.e. how often this address has "received" Bitcoins.
Does this "Tx" come from blockchain/blockexplorer terminology? Or why is it called "Tx" ("transmit") and not "Rx" ("receive")? To be clarified.
}

'''In the "Contacts" tab (foreign addresses):'''

The number in the Tx column indicates the total number of Bitcoin transactions that have ever been carried out from addresses of the current wallet towards this contact address

===What does the "Balance" column mean in Electrum?===
* Expert Mode only
* Applies to "Receive" tab only (i.e. own wallet's addresses).

The balance column indicates the amount of Bitcoins belonging to the given address.
The individual balances add up to the total balance of your wallet.

===What does the "Flag" column mean in Electrum?===
* Expert Mode only
* Applies to "Receive" tab only (i.e. own wallet's addresses).

This column indicates certain properties of the different addresses:
* C = [[#Change Addresses|Change address]] (without a "C" it means it is a [[#Normal Addresses|normal address]])
* P = Prioritized address
* F = Frozen address
* I = [[#Imported Addresses|Imported address]]

Note: P and F flags can be applied to both [[#Normal Addresses|normal]] and [[#Change Addresses|change]] addresses, and also to [[#Imported Addresses|imported addresses]].

===What do colors mean?===
In the Receive tab:
*green = prioritized
*blue = frozen
In the Contacts tab:
*gray = alias

==Troubleshooting==

=== 'transaction rejected by memorypool' errors ===

When you send a transaction, there is a delay before the Electrum client displays the transaction in its history.
This is because the server polls bitcoind's memorypool every 10 seconds.

If you create another transaction during this interval, during which the first tx is not displayed,
then your client will pick the same coins again, and the transaction will be rejected as a double spend.

==External Links==
* [http://ecdsa.org/electrum Electrum] project website
* [https://gitorious.org/electrum Electrum] project source (gitorius)
* [https://bitcointalk.org/index.php?topic=50936.msg950497#msg950497 Electrum Forum] - here this documentation was started

Electrum/Documentation

2012-06-14T08:16:23Z

ThomasV: /* Open/Unclear Points */

==Documentation of Electrum Bitcoin Client (Focus on the GUI)==
This page tries to document certain aspects of the [[Electrum|Electrum]] Bitcoin Client. The focus is on explaining certain aspects of its GUI, such that it gets easier for the user to understand its use.

More documentation, especially with regard to command line parameters, can be found at the parent page of this Wiki, i.e. [[Electrum|here]].

===Version Info===
Unless stated otherwise in particular sub-sections, the present state of this documentation is based on
* '''Electrum version 0.58'''
As this documentation gets updated, this "version info" can be updated, too!

Later versions of Electrum may add new features or deviate from this description to some extend.

===Open/Unclear Points===

Discussions about unclear points should take place on the [[Talk:Electrum/Documentation|Discussion page.]]

==What is a "Wallet" and a "Bitcoin Address"?==
* (General, not specific to Electrum)

Your wallet is a list of Bitcoin addresses (more precisely: a list of privat/public key pairs). Each address "contains" (or is associated with) a certain amount of Bitcoins at a given time.

Your wallet's balance is the sum of all Bitcoins of all your wallet's Bitcoin addresses.

Your wallet consists of both [[#Normal Addresses|normal addresses]] and [[#Change Addresses|change addresses]]. Although they are fully equivalent from the Bitcoin protocol's point of view, they are different in how they are used by Bitcoin clients like Electrum.

===Normal Addresses===
* (More or less general, not too specific to Electrum)
====How are New "Normal Addresses" Created for my Wallet?====
A Bitcoin client allows you to trigger the generation of a new Bitcoin address either manually, or it generates new addresses automatically upon certain conditions. The latter applies to Electrum: Depending on the "[[#What is the "Gap Limit"?|gap limit]]" setting in Electrum's program preferences, there will always be a certain number of unused addresses showing up in your list of receive addresses (=your own wallet's addresses), and as these addresses get used, new ones will show up automatically.

Typically you want to use a new address for receiving Bitcoins from somebody, instead of using any of your wallet's present addresses that have already been used for earlier transactions. This is to protect your privacy, because all Bitcoins transfers are published in the blockchain and can be read by anyone.

Another way of adding addresses to your wallet is to [[#Imported Addresses|import]] private keys (with their addresses of course), using Electrum's [[Electrum|command line options]]. See section about [[#Imported Addresses|imported addresses]] for more details.

===Change Addresses===
* (More or less general, not too specific to Electrum)
====What is a "Change Address", and why is it useful?====
The concept of change addresses is a feature not of the Bitcoin protocol, but of a Bitcoin client. It is implemented not only in Electrum but in most Bitcoin clients, including the original "Satoshi" Bitcoin client.

'''How it works:'''

Whenever your Bitcoin client (e.g. Electrum) sends Bitcoins from your wallet's address "A" to a foreing address "B", a new change address "C" is created by Electrum and added to your wallet.

Example: Address "A" has 20 BTC. Electrum sends 9 BTC from "A" to "B". The change (20-9 = 11 BTC) is sent to the "change address" "C". For this purpose, address "C" is created by Electrum at this moment and added to your wallet.

Exception: If all the Bitcoins of "A" are sent to "B", there is no need for creating a change address "C".

Actually, Bitcoin clients can also work without change addresses. In this case, the change would be sent back to "A" instead of the new address "C".

'''Why the concept of "change addresses" is useful:'''

* Using a new change address makes it more difficult for other people (by analyzing the blockchain) to track how many Bitcoins you have or where you're spending them.
* It also conceals which output is the "spend" and which is the "change".

===Imported Addresses===
Instead of generating new addresses in the default way from the wallet's [[#Seed|seed]], Electrum also allows you to import addresses (and their private keys of course) from external sources, e.g. from another Bitcoin client's wallet. For this, use Electrum's [[Electrum|command line]] options. Note that imported addresses cannot be recovered from your wallet's [[#Seed|seed]] and therefore need to be secured separately for a complete backup of your wallet.

Imported addresses can be used like any other [[#Normal Addresses|normal]] receive address with Electrum for transmission or reception of Bitcoins, and can also be (un)tagged as [[#What does it mean to "Prioritize" or "Freeze" Addresses in Electrum?|"prioritized" or "frozen"]].

===Deterministic Wallet===
====What is a "Deterministic Wallet" in Electrum?====
Traditionally, all new addresses (incl. the private keys of course) added to the wallet ([[#Normal Addresses|normal addresses]] or [[#Change Addresses|change addresses]]) are generated randomly. This is the case e.g. for the original "Satoshi Bitcoin Client" (at least as of today, version 0.6.2).

Contrary to that, a Bitcoin client with a "Deterministic Wallet" will generate all new addresses accoding to a pre-defined (i.e. "deterministic") algorithm as a function of a wallet-specific [[#Seed|seed]], which is a 128 bit number. This means, if the seed is known, all new addresses that Electrum will ever create for this wallet are known, because Electrum's algorithm is known (and open source).
This is a big advantage when it comes to making wallet backups:
* ''Traditionally'', a wallet backup just contains the bitcoin addresses (and private keys of course) that have been created by the client by the time the backup was made. If the user performs transactions after the backup, new addresses ([[#Normal Addresses|normal]] or [[#Change Addresses|change]] addresses) will be generated and added to the wallet. These are not included in the backup yet. If the wallet in use gets lost, all the Bitcoins that are associated with the new addresses will also be lost. To avoid the risk of a too high loss, regular wallet backups are important.
* ''With a Deterministic Wallet'' (like with Electrum), the wallet backup only needs to contain the seed, and all new addresses generated in the future are already secured by the initial backup. Hence, regular new backups are not required!

===Seed===
====What is the "Seed" of a Deterministic Wallet in Electrum?====
The Seed of a [[#Deterministic Wallet|deterministic wallet]] is a series of 128 random bits in Electrum.
For convenience, a seed can also be expressed by a sequence of 12 words in Electrum, and it also supports generation of a QR code to facilitate the backup of the seed.

So there are 2^128 possible seeds for a deterministic wallet in Electrum.
For comparison, the total number of Bitcoin addresses is 2^160, and the number of atoms on earth is 2^166.
So there exists one Bitcoin address per 1 Million atoms on earth, and there exists one seed of Electrum wallets per 4.3 Billion Bitcoin addresses.
(By the way: The number of atoms in the complete universe is estimated as 2^266).

===What is the "Gap Limit"?===

The gap limit is the maximal number of contiguous unused addresses in your deterministic sequence of addresses.

If you recover your wallet from seed, you will notice that the gap limit is asked by the recovery dialog.
It is used in order to decide when to stop the recovery procedure.

If you need to have more receiving addresses in your wallet, you may increase your gap limit (expert mode).
This, however, means that you will need to remember the new limit in order to be able to recover your wallet from seed.

{

To avoid misunderstandings and panic: This does not mean that you will irrecoverably loose your funds when you have forgotten the gap limit and want to recover your wallet from seed. It just means:
* If you enter a too low gap limit when recovering a wallet from seed, it may happen that some of the later addresses in the deterministic sequence of addresses are not recovered although they have a balance>0, such that your wallet will not show the full balance.
* If you enter a too high value for the gap limit when recovering a wallet from seed, you will unnecessarily generate too many new addresses that will then show up in your wallet, all with zero balance. But at least all your funds are recovered in this case.

}

==More on the Electrum GUI==
===What does it mean to "Prioritize" or "Freeze" Addresses in Electrum?===
When sending Bitcoins to a foreign address, Electrum will by default use a built-in method to select the address(es) of the wallet used for sending these Bitcoins.

* When you ''prioritize'' some of your wallet's addresses, these addresses will be used with preference. Other addresses will not be used until the prioritized addresses contain no more Bitcoins.
* When you ''freeze'' some of your wallet's addresses, these addresses will not be used for sending bitcoins. Instead, other addresses will be used. Sending Bitcoins is not possible if the non-frozen addresses of your wallet do not contain enough funds.

The user can (de)prioritize or (un)freeze both [[#Normal Addresses|normal]] and [[#Change Addresses|change]] addresses.

Note: Clearly, an address can not be "prioritized" and "frozen" at the same time.

===What does the "Tx" column mean in Electrum?===
* Expert Mode only
* Applies to "Receive" tab (own wallet's addresses) and "Contacts" tab (foreing addresses).

Tx stands for {... ?? "Transaction"? "Transmission" ?? ...}

The Tx column in Electrum displays a number for each Bitcoin address in the address list, both for own addresses ("Receive" tab) and for foreing addresses ("Contacts" tab).

'''In the "Receive" tab (own addresses):'''

The number in the Tx column indicates the total number of _incoming_ Bitcoin transactions that have ever been sent to this address.

{
The number of outgoing transactions is apparently not counted. It is unclear why the column is called "Tx" and not "Rx", because it indicates the number of times that Bitcoins have been sent to this address, i.e. how often this address has "received" Bitcoins.
Does this "Tx" come from blockchain/blockexplorer terminology? Or why is it called "Tx" ("transmit") and not "Rx" ("receive")? To be clarified.
}

'''In the "Contacts" tab (foreign addresses):'''

The number in the Tx column indicates the total number of Bitcoin transactions that have ever been carried out from addresses of the current wallet towards this contact address

===What does the "Balance" column mean in Electrum?===
* Expert Mode only
* Applies to "Receive" tab only (i.e. own wallet's addresses).

The balance column indicates the amount of Bitcoins belonging to the given address.
The individual balances add up to the total balance of your wallet.

===What does the "Flag" column mean in Electrum?===
* Expert Mode only
* Applies to "Receive" tab only (i.e. own wallet's addresses).

This column indicates certain properties of the different addresses:
* C = [[#Change Addresses|Change address]] (without a "C" it means it is a [[#Normal Addresses|normal address]])
* P = Prioritized address
* F = Frozen address
* I = [[#Imported Addresses|Imported address]]

Note: P and F flags can be applied to both [[#Normal Addresses|normal]] and [[#Change Addresses|change]] addresses, and also to [[#Imported Addresses|imported addresses]].

===What do colors mean?===
In the Receive tab:
*green = prioritized
*blue = frozen
In the Contacts tab:
*gray = alias

==Troubleshooting==

=== 'transaction rejected by memorypool' errors ===

When you send a transaction, there is a delay before the Electrum client displays the transaction in its history.
This is because the server polls bitcoind's memorypool every 10 seconds.

If you create another transaction during this interval, during which the first tx is not displayed,
then your client will pick the same coins again, and the transaction will be rejected as a double spend.

==External Links==
* [http://ecdsa.org/electrum Electrum] project website
* [https://gitorious.org/electrum Electrum] project source (gitorius)
* [https://bitcointalk.org/index.php?topic=50936.msg950497#msg950497 Electrum Forum] - here this documentation was started

Electrum/Documentation

2012-06-14T08:15:59Z

ThomasV: /* Open/Unclear Points */

==Documentation of Electrum Bitcoin Client (Focus on the GUI)==
This page tries to document certain aspects of the [[Electrum|Electrum]] Bitcoin Client. The focus is on explaining certain aspects of its GUI, such that it gets easier for the user to understand its use.

More documentation, especially with regard to command line parameters, can be found at the parent page of this Wiki, i.e. [[Electrum|here]].

===Version Info===
Unless stated otherwise in particular sub-sections, the present state of this documentation is based on
* '''Electrum version 0.58'''
As this documentation gets updated, this "version info" can be updated, too!

Later versions of Electrum may add new features or deviate from this description to some extend.

===Open/Unclear Points===
Text in curly brackets {like this} means that the author(s) of this documentation are not really sure about this...

--> other authors are welcome to correct/clarify

Discussions should take place on the [[Talk:Electrum/Documentation|Discussion page.]]

==What is a "Wallet" and a "Bitcoin Address"?==
* (General, not specific to Electrum)

Your wallet is a list of Bitcoin addresses (more precisely: a list of privat/public key pairs). Each address "contains" (or is associated with) a certain amount of Bitcoins at a given time.

Your wallet's balance is the sum of all Bitcoins of all your wallet's Bitcoin addresses.

Your wallet consists of both [[#Normal Addresses|normal addresses]] and [[#Change Addresses|change addresses]]. Although they are fully equivalent from the Bitcoin protocol's point of view, they are different in how they are used by Bitcoin clients like Electrum.

===Normal Addresses===
* (More or less general, not too specific to Electrum)
====How are New "Normal Addresses" Created for my Wallet?====
A Bitcoin client allows you to trigger the generation of a new Bitcoin address either manually, or it generates new addresses automatically upon certain conditions. The latter applies to Electrum: Depending on the "[[#What is the "Gap Limit"?|gap limit]]" setting in Electrum's program preferences, there will always be a certain number of unused addresses showing up in your list of receive addresses (=your own wallet's addresses), and as these addresses get used, new ones will show up automatically.

Typically you want to use a new address for receiving Bitcoins from somebody, instead of using any of your wallet's present addresses that have already been used for earlier transactions. This is to protect your privacy, because all Bitcoins transfers are published in the blockchain and can be read by anyone.

Another way of adding addresses to your wallet is to [[#Imported Addresses|import]] private keys (with their addresses of course), using Electrum's [[Electrum|command line options]]. See section about [[#Imported Addresses|imported addresses]] for more details.

===Change Addresses===
* (More or less general, not too specific to Electrum)
====What is a "Change Address", and why is it useful?====
The concept of change addresses is a feature not of the Bitcoin protocol, but of a Bitcoin client. It is implemented not only in Electrum but in most Bitcoin clients, including the original "Satoshi" Bitcoin client.

'''How it works:'''

Whenever your Bitcoin client (e.g. Electrum) sends Bitcoins from your wallet's address "A" to a foreing address "B", a new change address "C" is created by Electrum and added to your wallet.

Example: Address "A" has 20 BTC. Electrum sends 9 BTC from "A" to "B". The change (20-9 = 11 BTC) is sent to the "change address" "C". For this purpose, address "C" is created by Electrum at this moment and added to your wallet.

Exception: If all the Bitcoins of "A" are sent to "B", there is no need for creating a change address "C".

Actually, Bitcoin clients can also work without change addresses. In this case, the change would be sent back to "A" instead of the new address "C".

'''Why the concept of "change addresses" is useful:'''

* Using a new change address makes it more difficult for other people (by analyzing the blockchain) to track how many Bitcoins you have or where you're spending them.
* It also conceals which output is the "spend" and which is the "change".

===Imported Addresses===
Instead of generating new addresses in the default way from the wallet's [[#Seed|seed]], Electrum also allows you to import addresses (and their private keys of course) from external sources, e.g. from another Bitcoin client's wallet. For this, use Electrum's [[Electrum|command line]] options. Note that imported addresses cannot be recovered from your wallet's [[#Seed|seed]] and therefore need to be secured separately for a complete backup of your wallet.

Imported addresses can be used like any other [[#Normal Addresses|normal]] receive address with Electrum for transmission or reception of Bitcoins, and can also be (un)tagged as [[#What does it mean to "Prioritize" or "Freeze" Addresses in Electrum?|"prioritized" or "frozen"]].

===Deterministic Wallet===
====What is a "Deterministic Wallet" in Electrum?====
Traditionally, all new addresses (incl. the private keys of course) added to the wallet ([[#Normal Addresses|normal addresses]] or [[#Change Addresses|change addresses]]) are generated randomly. This is the case e.g. for the original "Satoshi Bitcoin Client" (at least as of today, version 0.6.2).

Contrary to that, a Bitcoin client with a "Deterministic Wallet" will generate all new addresses accoding to a pre-defined (i.e. "deterministic") algorithm as a function of a wallet-specific [[#Seed|seed]], which is a 128 bit number. This means, if the seed is known, all new addresses that Electrum will ever create for this wallet are known, because Electrum's algorithm is known (and open source).
This is a big advantage when it comes to making wallet backups:
* ''Traditionally'', a wallet backup just contains the bitcoin addresses (and private keys of course) that have been created by the client by the time the backup was made. If the user performs transactions after the backup, new addresses ([[#Normal Addresses|normal]] or [[#Change Addresses|change]] addresses) will be generated and added to the wallet. These are not included in the backup yet. If the wallet in use gets lost, all the Bitcoins that are associated with the new addresses will also be lost. To avoid the risk of a too high loss, regular wallet backups are important.
* ''With a Deterministic Wallet'' (like with Electrum), the wallet backup only needs to contain the seed, and all new addresses generated in the future are already secured by the initial backup. Hence, regular new backups are not required!

===Seed===
====What is the "Seed" of a Deterministic Wallet in Electrum?====
The Seed of a [[#Deterministic Wallet|deterministic wallet]] is a series of 128 random bits in Electrum.
For convenience, a seed can also be expressed by a sequence of 12 words in Electrum, and it also supports generation of a QR code to facilitate the backup of the seed.

So there are 2^128 possible seeds for a deterministic wallet in Electrum.
For comparison, the total number of Bitcoin addresses is 2^160, and the number of atoms on earth is 2^166.
So there exists one Bitcoin address per 1 Million atoms on earth, and there exists one seed of Electrum wallets per 4.3 Billion Bitcoin addresses.
(By the way: The number of atoms in the complete universe is estimated as 2^266).

===What is the "Gap Limit"?===

The gap limit is the maximal number of contiguous unused addresses in your deterministic sequence of addresses.

If you recover your wallet from seed, you will notice that the gap limit is asked by the recovery dialog.
It is used in order to decide when to stop the recovery procedure.

If you need to have more receiving addresses in your wallet, you may increase your gap limit (expert mode).
This, however, means that you will need to remember the new limit in order to be able to recover your wallet from seed.

{

To avoid misunderstandings and panic: This does not mean that you will irrecoverably loose your funds when you have forgotten the gap limit and want to recover your wallet from seed. It just means:
* If you enter a too low gap limit when recovering a wallet from seed, it may happen that some of the later addresses in the deterministic sequence of addresses are not recovered although they have a balance>0, such that your wallet will not show the full balance.
* If you enter a too high value for the gap limit when recovering a wallet from seed, you will unnecessarily generate too many new addresses that will then show up in your wallet, all with zero balance. But at least all your funds are recovered in this case.

}

==More on the Electrum GUI==
===What does it mean to "Prioritize" or "Freeze" Addresses in Electrum?===
When sending Bitcoins to a foreign address, Electrum will by default use a built-in method to select the address(es) of the wallet used for sending these Bitcoins.

* When you ''prioritize'' some of your wallet's addresses, these addresses will be used with preference. Other addresses will not be used until the prioritized addresses contain no more Bitcoins.
* When you ''freeze'' some of your wallet's addresses, these addresses will not be used for sending bitcoins. Instead, other addresses will be used. Sending Bitcoins is not possible if the non-frozen addresses of your wallet do not contain enough funds.

The user can (de)prioritize or (un)freeze both [[#Normal Addresses|normal]] and [[#Change Addresses|change]] addresses.

Note: Clearly, an address can not be "prioritized" and "frozen" at the same time.

===What does the "Tx" column mean in Electrum?===
* Expert Mode only
* Applies to "Receive" tab (own wallet's addresses) and "Contacts" tab (foreing addresses).

Tx stands for {... ?? "Transaction"? "Transmission" ?? ...}

The Tx column in Electrum displays a number for each Bitcoin address in the address list, both for own addresses ("Receive" tab) and for foreing addresses ("Contacts" tab).

'''In the "Receive" tab (own addresses):'''

The number in the Tx column indicates the total number of _incoming_ Bitcoin transactions that have ever been sent to this address.

{
The number of outgoing transactions is apparently not counted. It is unclear why the column is called "Tx" and not "Rx", because it indicates the number of times that Bitcoins have been sent to this address, i.e. how often this address has "received" Bitcoins.
Does this "Tx" come from blockchain/blockexplorer terminology? Or why is it called "Tx" ("transmit") and not "Rx" ("receive")? To be clarified.
}

'''In the "Contacts" tab (foreign addresses):'''

The number in the Tx column indicates the total number of Bitcoin transactions that have ever been carried out from addresses of the current wallet towards this contact address

===What does the "Balance" column mean in Electrum?===
* Expert Mode only
* Applies to "Receive" tab only (i.e. own wallet's addresses).

The balance column indicates the amount of Bitcoins belonging to the given address.
The individual balances add up to the total balance of your wallet.

===What does the "Flag" column mean in Electrum?===
* Expert Mode only
* Applies to "Receive" tab only (i.e. own wallet's addresses).

This column indicates certain properties of the different addresses:
* C = [[#Change Addresses|Change address]] (without a "C" it means it is a [[#Normal Addresses|normal address]])
* P = Prioritized address
* F = Frozen address
* I = [[#Imported Addresses|Imported address]]

Note: P and F flags can be applied to both [[#Normal Addresses|normal]] and [[#Change Addresses|change]] addresses, and also to [[#Imported Addresses|imported addresses]].

===What do colors mean?===
In the Receive tab:
*green = prioritized
*blue = frozen
In the Contacts tab:
*gray = alias

==Troubleshooting==

=== 'transaction rejected by memorypool' errors ===

When you send a transaction, there is a delay before the Electrum client displays the transaction in its history.
This is because the server polls bitcoind's memorypool every 10 seconds.

If you create another transaction during this interval, during which the first tx is not displayed,
then your client will pick the same coins again, and the transaction will be rejected as a double spend.

==External Links==
* [http://ecdsa.org/electrum Electrum] project website
* [https://gitorious.org/electrum Electrum] project source (gitorius)
* [https://bitcointalk.org/index.php?topic=50936.msg950497#msg950497 Electrum Forum] - here this documentation was started

2012-06-12T05:14:03Z

ThomasV: /* What is the "Gap Limit" in Electrum? (YET UNCLEAR IN THIS WIKI !!!) */

==Documentation of Electrum Bitcoin Client (Focus on the GUI)==
This page tries to document certain aspects of the [[Electrum|Electrum]] Bitcoin Client. The focus is on explaining certain aspects of its GUI, such that it gets easier for the user to understand its use.

More documentation, especially with regard to command line parameters, can be found at the parent page of this Wiki, i.e. [[Electrum|here]].

==How to Read this Documentation==
* Text in curly brackets {like this} means that the authour(s) of this documentation are not really sure about this... --> other people are welcome to correct/clarify

==What is a "Wallet" and a "Bitcoin Address"?==
* (General, not specific to Electrum)

Your wallet is a list of Bitcoin addresses (more precisely: a list of privat/public key pairs). Each address "contains" (or is associated with) a certain amount of Bitcoins at a given time.

Your wallet's balance is the sum of all Bitcoins of all your wallet's Bitcoin addresses.

Your wallet consists of both [[#Normal Addresses|normal addresses]] and [[#Change Addresses|change addresses]]. Although they are fully equivalent from the Bitcoin protocol's point of view, they are different in how they are used by Bitcoin clients like Electrum.

===Normal Addresses===
* (More or less general, not too specific to Electrum)
====How are New "Normal Addresses" Created for my Wallet?====
The Bitcoin client (e.g. Electrum) allows you to trigger manually the generation of a new Bitcoin address. You typically want to create a new address when you want to receive Bitcoins from somebody and do not want to use any of the wallet's present addresses that have already been used for earlier Bitcoin transfers, for privacy reasons (note that all transfers are publically visible in the blockchain).

===Change Addresses===
* (More or less general, not too specific to Electrum)
====What is a "Change Address", and why is it useful?====
The concept of change addresses is a feature not of the Bitcoin protocol, but of a Bitcoin client. It is implemented not only in Electrum but in most Bitcoin clients, including the original "Satoshi" Bitcoin client.

'''How it works:'''

Whenever your Bitcoin client (e.g. Electrum) sends Bitcoins from your wallet's address "A" to a foreing address "B", a new change address "C" is created by Electrum and added to your wallet.

Example: Address "A" has 20 BTC. Electrum sends 9 BTC from "A" to "B". The change (20-9 = 11 BTC) is sent to the "change address" "C". For this purpose, address "C" is created by Electrum at this moment and added to your wallet.

Exception: If all the Bitcoins of "A" are sent to "B", there is no need for creating a change address "C".

Actually, Bitcoin clients can also work without change addresses. In this case, the change would be sent back to "A" instead of the new address "C".

'''Why the concept of "change addresses" is useful:'''

* Using a new change address makes it more difficult for other people (by analyzing the blockchain) to track how many Bitcoins you have or where you're spending them.
* It also conceals which output is the "spend" and which is the "change".

===Deterministic Wallet===
====What is a "Deterministic Wallet" in Electrum?====
Traditionally, all new addresses (incl. the private keys of course) added to the wallet ([[#Normal Addresses|normal addresses]] or [[#Change Addresses|change addresses]]) are generated randomly. This is the case e.g. for the original "Satoshi Bitcoin Client" (at least as of today, version 0.6.2).

Contrary to that, a Bitcoin client with a "Deterministic Wallet" will generate all new addresses accoding to a pre-defined (i.e. "deterministic") algorithm as a function of a wallet-specific [[#Seed|seed]], which is a 128 bit number. This means, if the seed is known, all new addresses that Electrum will ever create for this wallet are known, because Electrum's algorithm is known (and open source).
This is a big advantage when it comes to making wallet backups:
* ''Traditionally'', a wallet backup just contains the bitcoin addresses (and private keys of course) that have been created by the client by the time the backup was made. If the user performs transactions after the backup, new addresses ([[#Normal Addresses|normal]] or [[#Change Addresses|change]] addresses) will be generated and added to the wallet. These are not included in the backup yet. If the wallet in use gets lost, all the Bitcoins that are associated with the new addresses will also be lost. To avoid the risk of a too high loss, regular wallet backups are important.
* ''With a Deterministic Wallet'' (like with Electrum), the wallet backup only needs to contain the seed, and all new addresses generated in the future are already secured by the initial backup. Hence, regular new backups are not required! {or is this not entirely true?? It is not really clear if the "[[#Gap Limit|Gap Limit]]" plays a role here...?!? Can anybody clarify?!?}

===Seed===
====What is the "Seed" of a Deterministic Wallet in Electrum?====
The Seed of a [[#Deterministic Wallet|deterministic wallet]] is a series of 128 random bits in Electrum.
For convenience, a seed can also be expressed by a sequence of 12 words in Electrum, and it also supports generation of a QR code to facilitate the backup of the seed.

So there are 2^128 possible seeds for a deterministic wallet in Electrum.
For comparison, the total number of Bitcoin addresses is 2^160, and the number of atoms on earth is 2^166.
So there exists one Bitcoin address per 1 Million atoms on earth, and there exists one seed of Electrum wallets per 4.3 Billion Bitcoin addresses.
(By the way: The number of atoms in the complete universe is estimated as 2^266).

{

Open Point: It is _not clear_ whether the algorithm of deterministic address generation is designed such that for any two seeds "S1" and "S2" (out of the 2^128 possible different seeds) the following condition holds true:
* If 4.3 Billion (2^32 to be exact) new addresses are calculated from each S1 and from S2, does the algorithm guarantee that there will be no collision between the set of 2^32 addresses from S1 and the set of 2^32 addresses from S2?
If this condition does not hold true, it needs to be clarified whether the use of deterministic wallets still bares an acceptably low probability of address collisions.

}

===Gap Limit===
====What is the "Gap Limit" in Electrum? (YET UNCLEAR IN THIS WIKI !!!)====

The gap limit is the maximal number of contiguous unused addresses in your deterministic sequence of addresses.
It is the criterion used to decide when to stop the recovery from seed process.

{

Apparently, when you generate too many new addresses, you exceed the "gap limit" at some point - whatever this means... It appears to the first authour of this documentation that this could be dangerous somehow in the sense that the new addresses might not be recoverable from the wallet's seed...?!??!?? Or not?? Not clear at all...
Not clear what this means. Isn't the wallet "deterministic"? So why should their be a problem with a "gap limit"? What is its significance?

; Quote of Electrum's author ThomasV on v.0.54 of Electrum in the Bitcoin Forum:
: ''The 'receive' tab now has a 'new' button, that allows the user to create addresses beyond the wallet's gap limit. The user gets a warning, and addresses that are beyond the gap limit are displayed in red. The red color will remain until the gap has been filled. (in other words, to fill the gap you need to send coins to the last non-red address of your list).''

;Quote of Electrum's author ThomasV on v.0.55 of Electrum in the Bitcoin Forum:
: ''the 'receive' tab has a 'new' button that allows to create new addresses by raising the wallet's gap limit. Note that the gap limit can be lowered too. The dialog also displays the minimum value of the gap limit that can be set without losing any of your current addresses (this assumes you are connected, because it needs to compute the maximal gap of your sequence of addresses)''

}

==More on the Electrum GUI==
===What does it mean to "Prioritize" or "Freeze" Addresses in Electrum?===
When sending Bitcoins to a foreign address, Electrum will by default use a built-in method to select the address(es) of the wallet used for sending these Bitcoins.

* When you ''prioritize'' some of your wallet's addresses, these addresses will be used with preference. Other addresses will not be used until the prioritized addresses contain no more Bitcoins.
* When you ''freeze'' some of your wallet's addresses, these addresses will not be used for sending bitcoins but they will keep their balance. Instead, other addresses will be used. {To clarify: Will they still not be used if all other addresses have zero balance, such that sending Bitcoins is not possible although the wallet has a balance? Probably yes, just not 100% sure...}

The user can (de)prioritize or (un)freeze both [[#Normal Addresses|normal]] and [[#Change Addresses|change]] addresses.

Note: Clearly, an address can not be "prioritized" and "frozen" at the same time.

===What does the "Tx" column mean in Electrum?===
* Applies to "Receive" tab (own wallet's addresses) and "Contacts" tab (foreing addresses).

Tx stands for {... ?? "Transaction"? "Transmission" ?? ...}

The Tx column in Electrum displays a number for each Bitcoin address in the address list, both for own addresses ("Receive" tab) and for foreing addresses ("Contacts" tab).

'''In the "Receive" tab (own addresses):'''

The number in the Tx column indicates the total number of _incoming_ Bitcoin transactions that have ever been sent to this address.

{
The number of outgoing transactions is apparently not counted. It is unclear why the column is called "Tx" and not "Rx", because it indicates the number of times that Bitcoins have been sent to this address, i.e. how often this address has "received" Bitcoins.
Does this "Tx" come from blockchain/blockexplorer terminology? Or why is it called "Tx" ("transmit") and not "Rx" ("receive")? To be clarified.
}

'''In the "Contacts" tab (foreign addresses):'''

The number in the Tx column indicates the total number of Bitcoin transactions that have ever been received by this address
{from anyobody? or just from myself, i.e. from addresses in my wallet? - Probably the latter - to be confirmed...}.

===What does the "Balance" column mean in Electrum?===
* Applies to "Receive" tab only (i.e. own wallet's addresses).

The balance column indicates the amount of Bitcoins belonging to the given address.
The individual balances add up to the total balance of your wallet.

===What does the "Flag" column mean in Electrum?===
* Applies to "Receive" tab only (i.e. own wallet's addresses).

This column indicates certain properties of the different addresses:
* C = [[#Change Addresses|Change address]] (without a "C" it means it is a [[#Normal Addresses|normal address]])
* P = Prioritized address
* F = Frozen address

Note: P and F flags can be applied to both [[#Normal Addresses|normal]] and [[#Change Addresses|change]] addresses.

{Are any flags missing?}

==External Links==
* [http://ecdsa.org/electrum Electrum] project website
* [https://gitorious.org/electrum Electrum] project source (gitorius)
* [https://bitcointalk.org/index.php?topic=50936.msg950497#msg950497 Electrum Forum] - here this documentation was started