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1  Bitcoin / Development & Technical Discussion / Proof of authenticity (POA) using the bitcoin blockchain on: August 26, 2011, 04:25:45 PM
The purpose of the following method and script is to permit one to provide a proof of the authenticity of a document, that is prove that a document is the original version, that it has not been altered since it's first publication.
This can have several uses, such as proving authorship, or preventing an adversary from spreading disinformation or confusion about for instance the date and location of an event (e.g. if "Anonymous" wishes to coordinate a DDOS attack). Another example which triggered my interest in this is that of Breivik's manifesto of which some decided to spread altered versions in order to make the original message difficult to find and spread. (note: I do not support Breivik; I am merely providing a method that can help all people, regardless of their intention. In the end, this method benefits the Truth.)

The idea is to insert a hash of a document in a block before publishing said document. Then, as the blockchain grows, it becomes increasingly difficult to modify this block and the hash it contains, thus providing a cryptographic proof that this exact document existed at a certain point in time.
So, in order to be able to prove a document of mine is authentic I would first have to publish it's hash in the blockchain and then wait a sufficient amount of time for two things:
 - that the blockchain has grown sufficiently that modifying the block of my hash has become infeasible;
 - and more importantly, that enough time had elapsed that there would be no doubt in the eyes of my public that the document was not publicly available at the time I inserted the hash.
 Thus, depending on the situation, waiting weeks or months after insertion of the hash may be necessary before publishing.

Technically, there are several ways of inserting a hash in the blockchain.
One would be to send transactions of amounts which, once concatenated, would form the hash. This method is somewhat impractical.
Another is to generate a "false" bitcoin address formed from the hash and to send a small amount of bitcoins to it (e.g. one satoshi). This is the method implemented in my script.
Yet another would be to instead generate the bitcoin private key from the hash, by using it as seed for the pseudo-random number generator for instance, and later disclosing this private key to enable verification.

2  Bitcoin / Development & Technical Discussion / Bitcoin GUI: can't reject 0.01BTC fee when sending small transactions on: May 08, 2011, 04:32:11 PM
I see no reason why the bitcoin GUI shouldn't allow to send low priority transanctions when sending small amounts. It could just add a warning: "if you do not pay a fee, your transaction may take a long time to be processed (a day?)". Also (but I think this has been suggested already), it should be possible to pay "milliBTC" fees. Paying a 0.01BTC fee when you are sending 0.05BTC is just not acceptable.
3  Bitcoin / Development & Technical Discussion / need to check that binaries are generated from the exact source code on: May 05, 2011, 09:51:26 AM
There is obviously a need to check that the bitcoin binary is indeed produced by building the source code which has (hopefully) been thoroughly checked. Otherwise someone could potentially introduce a backdoor to for instance steal bitcoins. This is especially important since I suppose most people using bitcoins do not bother with compiling it and as we gather more users, there will be more and more people using the precompiled binary.

To quote the README.md file:
Quote
The master branch is regularly built and tested (by who? need people willing to be quality assurance testers), and periodically pushed to the subversion repo to become the official, stable, released bitcoin.

In order to check the binary we need to be able to reproduce it exactly from the source. For that, we need to know the exact version of the compiler used, the exact version of the libraries used, a script that reproduces every step of the building process (modifications to the makefile, stripping debug symbols, ...), and anything else that I may have forgotten.
So please, whoever is in charge of creating the compiled packages (Gavin Anderson?), give us all the information needed to check them.
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