Watching and spending from a huge number of offline private keys


Creating a manual offline transaction isn't super difficult, you just need to be careful and think about what you're doing.

Make sure you have the public bitcoin address and the private key before continuing.

Here's what I do (This assumes you are sending some BTC to one address, some back to yourself as change and some as a transaction fee)

Create a bootable Live linux CD Download and save it to a USB memory stick. Open and pasted it into a text editor This (from 3) is a list of all the unspent transactions for the bitcoin address, I like to manually pick the transactions I want to use as inputs. eg. if I want to send 1 bitcoin, I might reference a 0.5 and an 0.6 BTC transaction rather than a 5BTC transaction. Remember that the transactions are in 1/100,000,000ths of a bitcoin. Remove the transactions you don't want to use as...
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A deterministic wallet is a system of deriving keys from a single starting point known as a seed. The seed allows a user to easily back up and restore a wallet without needing any other information and can in some cases allow the creation of public addresses without the knowledge of the private key.


Early clients such as the Satoshi client generate a buffer of fresh random private keys to be used as receiving and change addresses in the future. This has the effect of invalidating backups after a short period when the keypool buffer (typically 100 addresses) is exhausted. Deterministic wallets can generate an unlimited number of addresses on the fly and as such don't suffer from this issue. As the addresses are generated in a known fashion rather than randomly some clients can be used on multiple devices without the risk of losing funds. Users can conveniently create a single backup of the seed in a human readable format that will last the life of the...

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Creating Bitcoin Private Keys with Dice

Hopefully you have heard of Bitcoin, the up-and-coming online virtual currency. Unlike normal currencies, which are run by governments, Bitcoin has no central authority or controlling organization. Instead, every computer that runs Bitcoin software has a chance to become part of the network, processing transactions and keeping things running smoothly. This makes Bitcoin the only currency that is truly by the people, for the people.

While many Bitcoin wallet apps are good enough to store everyday walking-around money, storing larger amounts of money requires extra security. This is no different from cash. For example, many stores will limit the amount of money in their cash registers and put the rest in their safe. This article explains a high-security method of storing Bitcoins.

Bitcoin Private Keys

The Bitcoin network is based on a distributed ledger, called the "blockchain". The blockchain contains a log of...

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The Public and Private key pair comprise of two uniquely related cryptographic keys (basically long random numbers). Below is an example of a Public Key:

3048 0241 00C9 18FA CF8D EB2D EFD5 FD37 89B9 E069 EA97 FC20 5E35 F577 EE31 C4FB C6E4 4811 7D86 BC8F BAFA 362F 922B F01B 2F40 C744 2654 C0DD 2881 D673 CA2B 4003 C266 E2CD CB02 0301 0001

The Public Key is what its name suggests - Public. It is made available to everyone via a publicly accessible repository or directory. On the other hand, the Private Key must remain confidential to its respective owner.

Because the key pair is mathematically related, whatever is encrypted with a Public Key may only be decrypted by its corresponding Private Key and vice versa.

For example, if Bob wants to send sensitive data to Alice, and wants to be sure that only Alice may be able to read it, he will encrypt the data with Alice's Public Key. Only Alice has access to her...

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One of the issues with Public Key Infrastructure (PKI) has always been a way to safely store and backup the private keys. Most of the time this is done by using a keydatabase for storing the keys or even an HSM in larger organizations. And the only backup solution I encountered so far was burning the key to a CD-R or storing it on an USB stick and putting them in a (physical) vault, controlled by the Security Office.

I have a smarter idea for offline backups!

Since a year or so, I have been looking at and using QR-codes: the ‘matrix barcode’ which really catches on in advertising, due to usage of all smartphones. I have been using them as part of a little promotion campaign for apples (!) and I was really surprised at the number of ‘scans’ (which was needed to enter a website).

But QR-codes can hold much more information than a URL or an electronic business card: The 40-M version seems to be able to hold enough information for a private 2048 bit RSA key. With a...

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Learn how to use the wallet class and craft custom transactions with it.


The Wallet class is one of the most important classes in bitcoinj. It stores keys and the transactions that assign value to/from those keys. It lets you create new transactions which spend the previously stored transactions outputs, and it notifies you when the contents of the wallet have changed.

You’ll need to learn how to use the Wallet to build many kinds of apps.

This article assumes you’ve read Satoshi’s white paper and the WorkingWithTransactions article.


For optimal operation the wallet needs to be connected to a BlockChain and a Peer or PeerGroup. The block chain can be passed a Wallet in its constructor. It will send the wallet blocks as they are received so the wallet can find and extract relevant transactions, that is, transactions which send or receive coins to keys stored within it. The Peer/Group will send the wallet transactions...

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Here’s something every bitcoin owner should know: the safety and security of your bitcoins is ultimately your responsibility.

Combining digital security knowledge as well as secure bitcoin storage is important if you don’t want your accounts hacked and bitcoins drained. Remember – bitcoin transactions are not reversible. To send or spend bitcoins, one must have access to both public and private keys. Private keys, especially, must be protected.

Types of Bitcoin Wallets

There are a few types of bitcoin wallets and they have varying security mechanism to ensure the safety of private keys.

Simplistically, bitcoin wallets can be divided into 5 types: desktop, mobile, online, hardware and paper wallets. Some types may overlap or used in combination with each other. I’m going to touch on what to expect from each type and feature a few examples you can try out.

Here are 14 secure bitcoin wallet options you can choose from.

Desktop wallet

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Wallets are containers for private keys, usually implemented as structured files or simple databases. Another method for making keys is deterministic key generation. Here you derive each new private key, using a one-way hash function from a previous private key, linking them in a sequence. As long as you can re-create that sequence, you only need the first key (known as a seed or master key) to generate them all. In this section we will examine the different methods of key generation and the wallet structures that are built around them.

Nondeterministic (Random) Wallets

In the first bitcoin clients, wallets were simply collections of randomly generated private keys. This type of wallet is called a Type-0 nondeterministic wallet. For example, the Bitcoin Core client pregenerates 100 random private keys when first started and generates more keys as needed, using each key only once. This type of wallet is nicknamed "Just a Bunch Of Keys," or JBOK, and such wallets...

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Put Simply, What Is “Bitcoin”?

Bitcoin is a digital currency system which does for money what email did for written communication. Using an ingenious blend of cryptography and peer-to-peer networking, it allows for near-instantaneous transfer of wealth over the internet, securely, in any quantity, for less than $0.01 in fees. Additionally, the mechanism by which Bitcoins are created guarantees that it cannot be faked or counterfeited. No banks or governments can devalue the currency by printing more of it. The entire schedule of Bitcoin generation was publicly announced in 2009 and cannot be changed.

What makes Bitcoin unique from other digital currencies is that there is no central authority — a property that experts previously thought was impossible for a currency system! The network is maintained simultaneously by all users of it at any given time, often through bitcoin cloud mining, driven by a mathematical algorithm that ensures all users can agree on the...

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-By Milly Bitcoin – April 7, 2013.

The safest way to store bitcoins is in an offline wallet. With Bitcoin the tradeoff for eliminating banks is a that the user is responsible for backing up and securing their wallet.

A wallet is a collection of Bitcoin addresses. The addresses are pair of cryptographic keys, a public key and a private key. The public key is related to the Bitcoin address and other people can know your public address. The PRIVATE key, on the other should stay PRIVATE. This is the key to your funds.

The PRIVATE keys must stay PRIVATE.

If the private key is lost you cannot recover the bitcoins, ever. If the private key is saved to media and that media fails (hard drive, thumb drive, unreadable CD, etc.) you cannot recover the bitcoins.

If someone copies your private key they can take your bitcoins and it is highly unlikely you will ever know who did it. Also, they transfer coins from your wallet at any time in the...

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Direct answers to your questions:

I) Technically this is not too difficult. Looping through every new transaction on each received new block does not take too many resources and checking each transaction against 100,000 public keys is no problem at all. However, I do not know of a tool that would do exactly so. (For example, blockparser can output all the balances of all the addresses in the entire block chain in under a minute.)

II) No. You can not transfer all the received bitcoins in one transaction as the maximum size for a transaction is 1 megabyte. That would be able to spend the money on, say, 4000 different addresses at once, but no more. Of course, you can give all the private keys to somebody else "all at once", which enables them to spend the coins - but such a party would be unlikely to accept the sale as successful before transferring all the coins in to new addresses, just in case you kept the private keys as well.

III) No, if you keep the...

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Like in real life, your wallet must be secured. Bitcoin makes it possible to transfer value anywhere in a very easy way and it allows you to be in control of your money. Such great features also come with great security concerns. At the same time, Bitcoin can provide very high levels of security if used correctly. Always remember that it is your responsibility to adopt good practices in order to protect your money.

Be careful with online services

You should be wary of any service designed to store your money online. Many exchanges and online wallets suffered from security breaches in the past and such services generally still do not provide enough insurance and security to be used to store money like a bank. Accordingly, you might want to use other types of Bitcoin wallets. Otherwise, you should choose such services very carefully. Additionally, using two-factor authentication is recommended.

Small amounts for everyday uses

A Bitcoin wallet is like a...

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Without a Bitcoin wallet, you can’t send or receive Bitcoin payments. So before you get bitcoins, you’ll need to buy, download, or create a bitcoin wallet.

Are you a new Bitcoin user? We highly recommend the free Breadwallet.

Have you been using Bitcoin for a while and want to upgrade your security practices? Then keep reading!

Types of Wallets

There are many different ways to use Bitcoin and so there are many different types of wallets:

Online bitcoin wallets. Wallets that can be accessed on the web from any internet connected device. Bitcoin hardware wallets. Physical devices designed to secure bitcoins. Software wallets. Wallet applications downloaded to your phone, computer or tablet. Paper wallets. Bitcoin private keys printed from an offline computer.

By the end of this article you’ll understand Bitcoin wallets and have a better idea about which type is right for you. Here are some factors to consider:

On the go? If you are...
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Bitcoin makes moving money across the internet incredibly easy, but that ease comes with risks.

There are plenty of ways someone can take your money, track your spending, or violate your privacy.

Fortunately, there are also some straightforward measures you can take to safeguard your digital currency and keep your spending habits private. Here are our top five tips to protect your bitcoins:

1. Keep separate wallets

If the wallet you use for spending bitcoin also contains your entire bitcoin holdings, your savings will be vulnerable to various types of abuse.

There is no limit to the number of bitcoin addresses (or wallets) that one person may have.

Therefore, you could easily have an address for spending money, an address for savings and even an address for receiving payments.

2. Don't keep your savings in a web wallet

Recently, there have been several cases of web wallets being hacked and subsequently...

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Advertising Practices

We strive to provide you with information about products and services you might find interesting and useful. Relationship-based ads and online behavioral advertising help us do that.

Here's how it works: We gather information about your online activities, such as the searches you conduct on our Sites and the pages you visit. This information may be used to deliver advertising on our Sites and offline (for example, by phone, email and direct mail) that's customized to meet specific interests you may have.

If you prefer that we do not use this information, you may opt out of online behavioral advertising. If you opt out, though, you may still receive generic advertising. In addition, financial advisors/Client Managers may continue to use information collected online to provide product and service information in accordance with account agreements.

Also, if you opt out of online behavioral advertising, you may still see ads when you...

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How does Electrum work?¶

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 created by Electrum has 128 bits of entropy. This means that it provides the same level of security as a Bitcoin private key...

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Wallet security can be broken down into two independent goals:

Protecting your wallet against loss. Protecting your wallet against theft.

In the case that your current wallet hasn't been protected adequately (e.g. put online with a weaker password):

Making a new secure wallet, using appropriate long-term protection.

For a brief overview see also: Wallet Security Dos and Don'ts

Cold wallets

A cold wallet generates and stores private wallet keys offline on a clean air-gapped computer. Unsigned transactions are generated online, transferred offline for verification and signing, and the signed transaction is transferred online to be transmitted to the Bitcoin network.

This allows funds to be managed offline in Cold storage. Used correctly a cold wallet is protected against online threats, such as viruses and hackers. Cold wallets are similar to hardware wallets, except that a general purpose computing device is used...

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The question of “how to store your bitcoins” is one of the most important decisions for a Bitcoin user to make, and that is why we have done an extremely thorough Bitcoin wallet review for all major Bitcoin wallets.

In this article we will perform bitcoin wallet reviews, including providing the current best option, by looking at ease of use, security and advanced features for the major wallets in each category: Online Bitcoin Wallets, Desktop Bitcoin Wallets and Mobile Bitcoin Wallets.

To save you some time our conclusion to maximize ease of use, security and advanced features is to use the most well rounded mobile bitcoin wallet (Android or Apple Store) coupled with the ultra-secure and advanced desktop bitcoin client Armory.

Regardless of what kind of electronic payment system you are using if you want to spend digital money then you need to have a digital wallet. Bitcoin differs from every other online payment system. Bitcoin has no central...

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