Hashcash

Hashcash is an approach to tackle the problem of spam by technical means. Each email is provided by the sender with a header that shows that the "virtual Porto " is paid in the form of a little computation time. The receiver can verify this with comparatively little effort.

The basic idea is that offenders who want to send millions of emails with very little costs, these expenses for every single e -mail can no longer afford.

An alleged by critics weak point of this method lies in the fact that spam is sent to the majority of trojan infected computers from the owner usually unnoticed today. The idea of the critics is that it is therefore easily possible for the perpetrators to provide sufficient computing power. However, this is not the case, because both the computing capacity and the number of vulnerable systems is limited. The idea that the problem is easy to circumvent by the use of ten or a hundred times more computers is erroneous because Hashcash increases the computational cost per mailed spam email by a factor of several million. Spammers would therefore require many millions more infected computers to work around the problem and carry on as before.

Hashcash causes trojan infected computers can not send more faster and more spam, as the Internet connection allows. The creation of a single token takes up much more CPU time than sending several thousand spam emails in real time. For example, the generation of a 24-bit token takes on a 2.53 GHz computer about 30 seconds. The bulk sending a spam email takes an average of less than one millisecond (even if the individual spam email takes longer ), because requests are overlapped on multiple servers. The CPU time spent on this, depending on the implementation in the single digit microsecond range or in the upper nanosecond range. So to send a message with Hashcash is a million times more expensive if you look at the actual computation time.

The bottleneck of a spam trojan shipping date is the Internet connection: Spam can without much computational effort in a manner transparent to be sent unnoticed. On a computer that needs to continuously generate tokens for spam under full load, other applications are slowed down noticeably. Fan running audibly louder, the battery life of notebooks will be significantly reduced ( depending on the model by up to 80-90 %). Such major changes to attract attention and motivate users are more likely to remove Trojans or prevent it.