Physical Bitcoin or spending Bitcoin offline is a topic that has been discussed since 2010, from paper wallets to Casascius Coins to OpenDime. A point-of-sales (POS) terminal called Bitcoin Box was proposed in 2015, offline transactions using NFC, but seems like the project is dead. Offline Bitcoin payments posses a number of security challenges. A paper titled Secure Wallet-Assisted Offline Bitcoin Payments with Double-Spender Revocation was published last year. The paper proposes the first solution for secure Bitcoin offline payments using an offline wallet with several novel security mechanisms to prevent double-spending and to verify the coin validity in offline setting.
There are three phases:
1. Online Bitcoin preloading.
2. Offline Bitcoin payment.
3. Online redemption of coins and revocation of double spending attacks.
In the first phase, the payer X generates pre-loading transaction τl (step 1) that transfers some bitcoins from her standard Bitcoin account x to the offline wallet’s account w, so that the balance of w becomes positive. This is done by means of standard online Bitcoin transaction, for which the network generates n-transaction confirmation n -Tl. In the second phase the payer X requests W to generate an offline transaction τo with the desired amount destined to the account y (step 3). In the third phase, the payee Y redeems the bitcoins he received offline by broadcasting τo into the Bitcoin network (step 4) and optionally obtaining network confirmation n -To (step 5). The network confirmation will only be issued, if the network has not detected a double-spending attack against τo. Otherwise, the payee Y will trigger an optional double-spender revocation procedure, which includes sending a double-spender revocation transaction τr (step 6) to the Bitcoin network and obtaining corresponding confirmation n -Tr (step 7).
A secure offline Bitcoin payment system would be a big boost for adoption.
https://www.ethz.ch/content/dam/ethz/special-interest/infk/inst-infsec/system-security-group-dam/research/publications/pub2017/asia084.pdfhttp://www.thebitcoinbox.com/PS: I am not good with technicalities, but did understand the basic outline so hopefully no technical questions
PS: To cover up for my lack of technical knowledge, there was another offline transactions idea proposed in 2013, quite simple to grasp, but might seem a tad absurd, How to use fiat currencies for Bitcoin offline transactions?
https://bitcointalk.org/index.php?topic=305590.0
