Most computer systems are far from being secure.
A lack of security - it is said - might hinder the developments of new information technologies. Everybody knows electronic transactions involve a more or less calculated risk. Rumors about insecurity let consumers doubt whether the commodity of e-commerce is bigger or its risks. First of all the market depends on the consumer's confidence. To provide that another application for public key cryptography gets essential: the digital signature, which is used to verify the authenticity of the sender of certain data.
It is done with a special private key, and the public key is verifying the signature. This is especially important if the involved parties do not know one another. The DSA (= Digital Signature Algorithm) is a public-key system which is only able to sign digitally, not to encrypt messages. In fact digital signature is the main-tool of cryptography in the private sector.
Digital signatures need to be given for safe electronic payment. It is a way to protect the confidentiality of the sent data, which of course could be provided by other ways of cryptography as well. Other security methods in this respect are still in development, like digital money (similar to credit cards or checks) or digital cash, a system that wants to be anonymous like cash, an idea not favored by governments as it provides many opportunities for money laundry and illegal transactions.
If intellectual property needs to be protected, a digital signature, together with a digital timestamp is regarded as an efficient tool.
In this context, the difference between identification and authentication is essential. In this context smartcards and firewalls are relevant, too.
A lot of digital transactions demand for passwords. More reliable for authentication are biometric identifiers, full of individual and unrepeatable codes, signatures that can hardly be forged.
For more terms of cryptography and more information see:
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With World War I an entire system of ideas how wars work collapsed. Suddenly it was no longer mostly soldiers who had to fight. War became an engagement of every day's life. Everybody got involved.
Propaganda therefore changed as well. The campaigns were no longer temporarily and recent but had to be planned for years. Who failed in organizing it or used the wrong keywords failed. Masters of modern propaganda became the British, whereas the Germans failed completely in the beginning.
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The water-clocks are an early long-distance-communication-system. Every communicating party had exactly the same jar, with a same-size-hole that was closed and the same amount of water in it. In the jar was a stick with different messages written on. When one party wanted to tell something to the other it made a fire-sign. When the other answered, both of them opened the hole at the same time. And with the help of another fire-sign closed it again at the same time, too. In the end the water covered the stick until the point of the wanted message.