What is the ruling on trading, selling and buying in digital currencies such as Bitcoin and other currencies?
His Eminence Sayyid al-Sistani has not answered this question yet due to a lack of sufficient information [related to the specifics, transactional procedures and valuation of bitcoin]. However, it would be useful to give the following explanation as guidance and general education until the Office in Holy Najaf issues an official a response.
Every legitimate transaction involves four essential components: the seller, the buyer, the item being sold/purchased, and the price, which the buyer pays (e.g. with money) to the seller in exchange for the item. For a transaction to be valid and acceptable from a jurisprudential (i.e. Islamically) standpoint, these four components must be clearly defined and clarified for both the buyer and seller in the market. Furthermore, there is also a set of other conditions that must be met for each one of these components.
Given that Bitcoin lacks the essential components of a [legitimate] transaction and fails to meet its conditions, or at least given that some of the conditions or the specific details of the item being sold (i.e. for which money would normally be paid in exchange) are not clear, it is not possible for the jurist to state that such a transaction is permissible from a jurisprudential perspective. Rather, spending money in exchange for it would be a kind of destruction, and destroying money is not religiously permissible.