user7107: Is there any centralized cryptocurrency? Is cryptocurrency a Bitcoin oriented concept only? From what i read almost all of the cryptocurrencies are derivatives of Bitcoin. 

user4708: I think you are correct that almost all of the cryptocurrencies are derivatives of Bitcoin.  From that fact it would follow that they would all be decentralized.
That being said, there are centralized aspects of cryptocurrencies, including Bitcoin.  For example, online wallets, exchanges and mining pools are all centralized.

user575: Cryptography-based currencies predate Bitcoin by decades. The most well-known is the work of David Chaum on blind signatures, described in some papers from around 1985. The most accessible description of his and other methods is actually this document from 1996.
In 1990 Chaum went on to found a company, called DigiCash, to offer such a currency.
What they offered had a lot going for it - you could store money as data on your computer, and you could transfer it anonymously. However, what it lacked was a decentralized transaction synchronization mechanism - synchronization was done on the company's central servers. Because of this, it did not achieve the support Bitcoin did, and the company went bankrupt in 1998.
A more modern platform is Open Transaction which is inspired by Chaum's ideas but offers much more functionality.
So the reason you don't hear about centralized crypto-currencies is not because they don't exist, but because they're mostly pointless. Only with the advent of decentralized transaction synchronization in Bitcoin and its clones we saw growth in this space beyond just academia.

7107: <p>Is there any centralized cryptocurrency? Is cryptocurrency a Bitcoin oriented concept only? From what i read almost all of the cryptocurrencies are derivatives of Bitcoin. </p>
 4708: <p>I think you are correct that almost all of the cryptocurrencies are derivatives of Bitcoin.  From that fact it would follow that they would all be decentralized.</p>

<p>That being said, there are centralized aspects of cryptocurrencies, including Bitcoin.  For example, online wallets, exchanges and mining pools are all centralized.</p>
 575: <p>Cryptography-based currencies predate Bitcoin by decades. The most well-known is the work of David Chaum on blind signatures, described in some papers from around 1985. The most accessible description of his and other methods is actually <a href="http://groups.csail.mit.edu/mac/classes/6.805/articles/money/nsamint/nsamint.htm" rel="nofollow">this</a> document from 1996.</p>

<p>In 1990 Chaum went on to found a company, called DigiCash, to offer such a currency.</p>

<p>What they offered had a lot going for it - you could store money as data on your computer, and you could transfer it anonymously. However, what it lacked was a decentralized transaction synchronization mechanism - synchronization was done on the company's central servers. Because of this, it did not achieve the support Bitcoin did, and the company went bankrupt in 1998.</p>

<p>A more modern platform is Open Transaction which is inspired by Chaum's ideas but offers much more functionality.</p>

<p>So the reason you don't hear about centralized crypto-currencies is not because they don't exist, but because they're mostly pointless. Only with the advent of decentralized transaction synchronization in Bitcoin and its clones we saw growth in this space beyond just academia.</p>
