Pavol Rusnak #cypherpunk #hacker #openhw #privacy #bitcoin #newmediaart

How to push Bitcoin transactions via SMS

Blockstream announced today their Satellite project. I was thinking about exactly that for quite long time, ever since this DVB-T broadcast experiment in 2014. There are lot of sceptics, but I am very excited about this development.

One of the recurring questions I saw was this one: What about the other direction (from user to Bitcoin node)?

Well, there are many options. One of them is sending new transactions via SMS or some other “legacy” method, if the Internet is not usable (blocked by the government, etc.).

I decided to create a simple proof of concept experiment named SMSPushTX. The source code is available from my GitHub repository.

First, I had to register at some service provider which is able to process inbound/incoming SMS. One of them is for example Nexmo, but there are others, such as Twilio or Tropo. I decided to go with Nexmo, because they have relatively cheap virtual numbers and also one does not have to pay for incoming messages, which is exactly what we (do not) want in our scenario!

After getting a virtual number (this was just 0.50 EUR/month for Belgian numbers), I was able to set up a Nexmo webhook which is triggered on each received SMS message. This webhook is pointed at my very simple Flask server in It consumes messages and forwards them to process_msg function in There is a catch, though. If a message is longer than 160 characters, you’ll need to concatenate it in your software manually, because Nexmo will send you a notification for every chunk separately. Luckily, that was quite easy, because you also get number of chunks and sequence number of current chunk in every notification.

Example of the incoming notifications:

    'concat-ref': '16',
    'msisdn': '420xxxxxxxxx',
    'messageId': '0C000000538BA945',
    'concat-total': '2',
    'message-timestamp': '2017-08-15 21:04:16',
    'concat-part': '1',
    'concat': 'true',
    'type': 'text',
    'to': '32460213730',
    'text': 'AQAAAAGKDYUXkeV/1wYLUD82slBs++d1BG+3l3VDzQsCk06KtAQAAABrSDBFAiEAhnJOYrejTqK/yeC7trGn/RhmQ13cCLjgI7KFmpPxxf4CIEj599L7S7r/WNFw63178y2cUHbQPtquhs3JtAcxxzyZA',

    'concat-ref': '16',
    'msisdn': '420xxxxxxxxx',
    'messageId': '0C000000538BAAA6',
    'concat-total': '2',
    'message-timestamp': '2017-08-15 21:04:17',
    'concat-part': '2',
    'concat': 'true',
    'type': 'text',
    'to': '32460213730',
    'text': 'SECK8N3vuXGrfZcC+wxfzyXVJtOnRaDDVVgU6RP/7vIKJj/////AgcEMwAAAAAAGXapFFmMuQgji+WAXhfI8FA1PGHHV8ZeiKxAQg8AAAAAABl2qRQkNDDiX+4AeooHtEj57drd3FbY54isAAAAAA==',
    'keyword': 'SECK8N3VUXGRFZCC',

Once the message is correctly concatenated, we can push it to Insight server using its API. I decided to allow two formats of transactions: hexadecimal format and base64 format. If sender uses the latter, we need to convert it to hexadecimal and only push to Insight server afterwards. This is done in pushtx function of

That’s it! That was easy right?! Remember, this is just a quick & dirty proof of concept and lots of things can (and should) be improved. But if one person is able to do something like this within 90 minutes with 10 EUR budget (10 EUR is minimum Nexmo payment, you will get 2 EUR as bonus, what translates to 2 years of Belgian number!), imagine what could be done with a little bit more resources!

Below is the screenshot of the base64 encoded transaction I sent to my service. It’s already mined in the blockchain after being successfully broadcasted via my service to the Bitcoin network.

You can try sending your own transactions via SMS here:

  • +32 460 213 730 (BE/EU)
  • +1 (314) 300-3730 (USA)

I will try to keep the service running for some time. Enjoy! :-)


How to use TREZOR with Rootstock (RSK) using MyEtherWallet

Since firmware 1.5.0 TREZOR supports Rootstock (RSK).

Update: MyEtherWallet can use RSK with TREZOR out of the box now! So this post is now obsolete.

To use RSK using MyEtherWallet one needs to point it to a RSK node which runs using HTTPS (not HTTP) and has correctly set Cross-Origin headers. Since there was none, I created one and sent a pull request to MyEtherWallet, so this chain can be used out of the box.

Until this pull request is accepted you can try it manually. Click on a menu in top-right corner, select the “Add Custom Node” item and fill in the following values:

Node Name:          RSK
Port:               (empty)
(chain):            Custom
Supports EIP-155:   yes
Chain ID:           31


Some useful links:


Longest TXID prefix collision in Bitcoin

As you probably know, transactions in Bitcoin are identified by their SHA256 hashes which are 256 bits long. These identifiers are called transaction ID or TXID.

We were brainstorming a new project at SatoshiLabs and an interesting question popped up. How much can we trim TXIDs before collisions start to appear? Or in another words: can we use just the first 128 bits of the hash instead of the full hash to uniquely identify the transaction? Can we use even less bits?

Let’s find out!

Bitcoin Core daemon provides a JSON RPC interface, which you can use to query the blockchain. There are many ways how you can interact with the RPC, but I prefer to use Python, so let’s use this as an example. Let’s install the required package first:

sudo pip install python-bitcoinrpc

Next, let’s open ~/.bitcoin/bitcoin.conf file and note the rpcuser and rpcpassword fields from the file, we’ll need it for later. If you want to access the RPC from different machine, add the following line:


This opens the RPC port for the specified range.

Now, let’s create the script with the following contents (modify the line containing RPC_SERVER to your needs):


from bitcoinrpc.authproxy import AuthServiceProxy

RPC_SERVER = ('bitcoinrpc', 'mysupersecretpassword', '', 8332) # user, pass, host, port

rpc = AuthServiceProxy('http://%s:%s@%s:%d' % RPC_SERVER)

count = rpc.getblockcount()

first = 0
chunk = 100

for start in range(first, count, chunk):
    end = min(start + chunk, count)
    rng = range(start, end)
    hashes = rpc.batch_([['getblockhash', h] for h in rng])
    blocks = rpc.batch_([['getblock', h] for h in hashes])
    for b in blocks:
        for t in b['tx']:

What this script does is that it opens RPC connection to the node and asks for the actual blockheight (index of the newest block).

Then it uses batch API to ask for hashes of individual blocks and contents of these blocks (you can’t ask for content of block #17 directly, you need to know its hash first). Once the contents of the block is known, the script just prints out transaction IDs to output and discards the rest.

Running the script produces a 13 GB text file with 201,180,597 lines (each line containing exactly one TXID and a newline).

Now we need to find a longest collision. Finding it is quite easy once we sort the file, because sorting will put collisions next to each other. This means we just go through the file and measure the length of the collision with the previous line.

I wrote another script in Python to perform the task, but it was too slow (I left it running for 20 minutes and then I stopped it).

I decided to rewrite it to C and cheated a little bit (I know that each row is exactly 64 characters + newline, so there’s no need to read the file row by row as a text file, but let’s read it rather as a 65-byte blocks):

#include <stdio.h>
#include <string.h>

int strsame(const char *s1, const char *s2, int max)
    int r = 0;
    while (r <= max) {
        if (*s1 != *s2) return r;
        r++; s1++; s2++;
    return r;

int main()
    FILE *f = fopen("txlist.sorted", "rb");

    char buf1[65], buf2[65];
    char res1[65], res2[65];

    memset(buf1, 0, sizeof(buf1));
    memset(buf2, 0, sizeof(buf2));

    char *line = buf1;
    char *last = buf2;
    int last_max = 0;

    for (;;) {
        size_t s = fread(line, 65, 1, f);
        if (!s) break;

        int r = strsame(line, last, 64);

        if (r > last_max) {
            last_max = r;
            memcpy(res1, line, 65);
            memcpy(res2, last, 65);

        char *tmp = line;
        line = last;
        last = tmp;

    printf("%.65s%.65s%d\n", res1, res2, last_max);


    return 0;

Running the program (it took just around 45 seconds!) resulted in the following output:


Woohoo! We have the result. The longest collision is 13 hex characters long and you can see it above.

This means 7 bytes (56 bits) are enough to distinguish the transactions by their TXID for now. Much less than I anticipated at the beginning!

Autoplay video on Raspberry Pi

Lots of (art) people are using Raspberry Pi instead of DVD players and MP4 players for their installations that play videos in loop.

There are many ways how to achieve the result, but the one I liked the most is the following:

  1. download Raspbian Lite from
  2. copy the downloaded image to the SD card, e.g. sudo dd_rescue 2017-01-11-raspbian-jessie-lite.img /dev/mmcblk0
  3. boot Raspberry Pi into freshly installed Raspbian
  4. copy your video from USB flash drive to the SD card
  5. sudo apt-get update
  6. sudo apt-get install omxplayer
  7. append this line /usr/bin/omxplayer -b --loop /home/pi/*.mp4 to file /etc/rc.local
  8. set the file as executable: chmod +x /etc/rc.local
  9. reboot and enjoy!

If you want something more magical (that can discover and autoplay all video files on attached USB stick), you can try VideoPi project by my friend Jakub.

TREZOR support in Tails 3.0

Tails project released a first beta version of their upcoming 3.0 release based on Debian 9 Stretch. See their call for testing for the official announcement.

There are lot of interesting changes, but the important one for me is that TREZOR now works out of the box in Electrum. No need to install any extra packages or create custom udev rules. As a bonus, you can use TREZOR from command line using trezorctl command.

PS: You cannot use TREZOR with our official TREZOR Wallet in Tails, because TOR Browser is configured in a way that it cannot reach TREZOR Bridge which is running as a localhost service.

If you want to test the release in QEMU like I do, follow these steps:

  1. download ISO image from the announcement above (currently tails-amd64-3.0-beta1.iso)
  2. install QEMU
  3. run lsusb | grep TREZOR, you should see line similar to this: Bus 002 Device 035: ID 534c:0001 SatoshiLabs Bitcoin Wallet [TREZOR]
  4. note the numbers 002 and 035, this is the physical address of the USB device
  5. run qemu-kvm -m 2048 -cdrom tails-amd64-3.0-beta1.iso -usb -device usb-host,hostbus=2,hostaddr=35 where 2 and 35 are numbers from step above
  6. if you run lsusb in Tails you should see the TREZOR device in the listing as well

You should never ever run Tails in a virtual machine, this is just for testing!!!