A distributed Digital currency backed by processing power was a fairly old idea at the time. The first time I heard about the idea was late 90's but I think it's earlier than that.
To have a currency backed by processing power is not really an old idea either. It was at most 10 years old and nobody really had a good idea how proof-of-work (POW) could make a currency at that time (around 1999). I'm referring to the "Bread Pudding" variant of MicroMint (http://www.hashcash.org/papers/bread-pudding.pdf), not Cryptonomicon which doesn't really mention distributed computing or POW.
The traditional approach would be a public ledger mantained by the 'miners' aka a block-chain. The the issue is that's not anonymous, but while a lot research went into creating an anonymous currency bitcoin was a MVP which took off. Now, I am not saying nothing about bitcoin was new, just the innovation was in the specific implementation not the overall idea.
Bit torrent was released in July 2001, bitcoin 2009 so the idea of distributed networks was fairly well established at the time.
PS: And yes, there was a lot of early criticism about the public nature of bitcoin.
Bittorrent was way easier because it was about copying, whereas a currency has to in a sense make copying impossible via some sort of time-stamping to prevent double-spend.
That's the point: No one knew how to do that before Satoshi.
> The traditional approach would be a public ledger mantained by the 'miners' aka a block-chain.
Are you joking? If you knew about the blockchain and miners before 2008, you could have simply created Bitcoin yourself and become multimillionaire.
> The the issue is that's not anonymous, but while a lot research went into creating an anonymous currency bitcoin was a MVP which took off.
The issue was no one knew how to create a trustless consensus mechanism. And Bitcoin is not anonymous, it's pseudonymous. True anonymity only became possible after Bytecoin's innovation in the use of ring signatures. Nowadays the most popular coin with true anonymity is Monero (created in 2014, as a fork of Bytecoin with a fair distribution).
> the innovation was in the specific implementation not the overall idea
Clearly you don't know what you are talking about.
> Bit torrent
What does that have to do with anything? Bittorrent doesn't use a blockchain.