How do crypto NFT stamps work? by@alfredodecandia

How do crypto NFT stamps work?

Alfredo de Candia HackerNoon profile picture

Alfredo de Candia

Author of "Mastering EOS" & "Mastering DeFi" blockchain specialist, android developer

2021 saw an explosion of the NFT sector, Non-Fungible Token, which are digital assets on blockchains, all of which are unique and different, thanks to their identifier registered on the blockchain that varies from NFT to NFT, a sector that has been pushed a lot by art and everything related to digital drawing in its various forms.

But in addition to associating an image to an NFT, it is possible to exploit the same technology to associate other things and even physical goods, as in the case of the first physical book connected to an NFT, and also effective as a tool for something more traditional as they can be the stamps.

And today we will analyze what has been done by the Swiss post office "La Posta" as it has created the first series of crypto NFT stamps, which are stamps in all respects but in addition, an NFT has also been created, indeed various NFTs, with specific designs linked to the Swiss panorama.

The news dates back to the end of September 2021 when it was announced that on November 25th, "Swiss Crypto Stamp" would be released and made available for purchase, i.e. Swiss stamps, worth 8.90 francs each, and linked to them, as there are 13 different stamps, there are as many NFTs. The characteristics of these stamps, in addition to performing their standard function, are accompanied by a wallet, a paper wallet, in which the relative NFT is saved, and an NFT which was created on the Polygon (MATIC) blockchain, which has already encountered several problems on his way.

Here, we are talking about 175 thousand NFTs, divided among 13 various designs and with various runs, which start from a minimum of 65 thousand (token ID: 1) up to only 50 copies (token ID: 13) and the same ones on the secondary market have already reached figures importantly, for example, the NFT with ID: 13, quote is already 5 ETH (about 20 thousand dollars).

How were they sold?

Going into the details of the whole process, we started with a direct sale on the Swiss post office site. Here, we are talking about a traditional sale through access to the site and purchase by credit card, as we were buying the physical stamp that had the related paper wallet, obviously they are now finished and can no longer be bought:


So by buying for the modest sum of 8.90 CHF, you were entitled with a copy of the stamp and the related paper wallet with the NFT inside, and only when the envelope with the stamp inside arrives, will we know the received NFT.

What’s inside the envelope?

And after a long wait, wherein people in some countries have waited over a month to receive what they bought a month ago, let's see how it looks like.

With an envelope on the outside, on which we can find the procedure to understand how it works:


Inside the envelope, we can see both, the traditional stamp and the paper wallet linked to it:


So on the left is the stamp, center contains the address of our wallet with relative QR code and the type of ID of the token (in this case, the ID: 1), and on the right is the private key of the same which is used for importing it into our digital wallet, such as MetaMask for example.

What’s in that address?

Since we are talking about the Polygon blockchain, we will have to check an explorer that supports this blockchain and then enter its address, and among the internal transactions to our address, we find a transaction coming from a smart contract to our address and with a value of 0.022 MATIC, this is the decoded smart contract:

#  Panoramix v4 Oct 2019 
#  Decompiled source of poly:0xC34053B4D81160f2268Bc21B517226FF87764cD6
#  Let's make the world open source 

def _fallback() payable: # default function

def airdrop(address[] _participants, uint256 _totalAmount) payable: 
  require calldata.size - 4 >=′ 64
  require _participants <= 18446744073709551615
  require _participants + 35 <′ calldata.size
  require _participants.length <= 18446744073709551615
  require _participants + (32 * _participants.length) + 36 <= calldata.size
  if _totalAmount and _participants.length > -1 / _totalAmount:
      revert with 'NH{q', 17
  if _totalAmount * _participants.length != call.value:
      revert with 0, 'INVALID_VALUE'
  idx = 0
  while idx < _participants.length:
      require cd[((32 * idx) + _participants + 36)] == addr(cd[((32 * idx) + _participants + 36)])
      call addr(cd[((32 * idx) + _participants + 36)]) with:
         value _totalAmount wei
           gas 2300 * is_zero(value) wei
      if not ext_call.success:
          revert with ext_call.return_data[0 len return_data.size]
      if idx == -1:
          revert with 'NH{q', 17
      idx = idx + 1

How to see our NFT?

Now we know that our NFT is located in our address, remember that this NFT exploits the ERC-1155, now in order to see it, we can make use of the OpenSea platform and simply write our Polygon address next to the, in our case the address is like this:

So it’s a very simple procedure and we will also be able to see the last market price of our NFT, which for the moment is at 0.0031 ETH.

How to sell our NFT?

If instead, we want to sell our NFT, then we have to scratch the right side of our wallet paper and insert the private key in a digital wallet such as MetaMask and then connect it to the OpenSea platform and proceed with the sale of the same.

Also in this case the process is quite simple, and for those wishing to deepen this aspect and the OpenSea platform, refer to the book "Mastering NFT - Practical Guide for beginners and not", written by me.

Other NFT stamps

These stamps, contrary to what one might think, are not the only crypto stamps created as there are several previous collections, such as those of the Austrian post office that also made NFT stamps, in that case with the ERC-721 standard, back in 2019, and so in the Arab Emirates there are related crypto stamps NFT launched in December 2021.


As we have seen, the NFT sector finds space in various fields, therefore, not only the artistic one but also in the traditional field such as these stamps, and other implementations are and will be made over time.

For Italian readers, I’ve made a video explaining all the processes: