Quote from: ChuckOne on May 17, 2014, 08:21:17 PM

A Blockchain Network User needs to verify or trust the software he uses anyway no matter if PoW or PoS.

That is true. It is an assumption in the security model. Of course you are stuck on the idea that the genesis block can be forged (because you are trying to support a logical fallacy) that you ignore far obvious examples of why this is true. If the attacker has compromised your node (hardware, operating system, node software) then you have no assurance you are part of the network at all. The attacker could steal your private keys, the attacker could have you generate weak private keys, the attacker could feed you false information ("yes block 123 is valid and contains your payment" when no such block or transaction even exists), the attacker could simply wait until you obtain a desired amount of wealth and then transfer it to an address he controls. You can't assume any level of security. If your node is compromised then you have no security at all.

So yes the security model assumes that the node (not just the client software, but hardware, operating system, and connectivity to the network at large) is secure.
It also assumes the cryptographic primitives used are cryptographically strong.
It also assumes the implementation makes no errors which weaken that security (duplicate k values in signing as an example).
It also assumes that no malicious entity have >50% of the critical resource (computing power and/or stake).

None of those assumptions are different for Pos vs PoW so they are irrelevant for a topic called "Proof of stake instead of proof of work". The one notable difference between PoS & PoW is that an attacker can use something he had at one time but no longer has to attack the network. This is commonly called the "PoS problem" but I think "history attack" is more descriptive. Taking a step back this is possible for PoS (and possibly other as of yet developed systems) due to the fact that what is being secured is also what is being used to secure it. The irreversibility of blockchain is being secured by records of the same blockchain*. In other words we are assuming the blockchain can't be modified because based on records in the blockchain not being modified. This property allows an attacker to reduce the cost and risk of an attack by selling off the stake and using the prior record of it to perform the attack.

Saying that one can simply disregard the longest chain by knowing which chain is correct by "code review" or "opinion of friends" is a logical fallacy. If you can disregard the longest chain, and pick a chain because it is "better" despite being equally valid, different, and shorter then you don't need PoS or PoW to begin with. You can just use your "code review" and "opinion of your friends" to determine the best chain at any point in time. Of course "opinion of friends" expanded to a global scale would be to connect to all known peers and ask them which chain is best. The issue is that the security model is weak and subject to sybill attack. The very reason PoW of PoS is used is because reaching a consensus based on what a majority of nodes think is weak. Can't you see the logical fallacy?

1) Chains may contain equally valid but different sets of transactions.
2) We can't just have nodes vote on the best chain as this is subject to a sybill attack and in a decentralized trustless network there is no known solution.
3) The solution is to have miners force a consensus using a critical resource (stake of computing power).
4) When a node has two competing chains that are both equally valid the chain which is the longest* is the best chain.

now here comes your fallacy
5) When the longest chain is "bad" we can just disregard it by asking our peers which one is the best which is a contradiction of #2.

If it were true the security model would simply be
1) Chains may contain equally valid but different sets of transactions.
2) When a node has two competing equally valid chains it asks its peers which one is the "best".

If you believe #5 is valid then the proof of work/stake is utterly pointless. You only follow it when it otherwise is in agreement on what you believe is best but when it disagrees with that you consult your peers. If that was a valid solution then just skip the pointless interim steps and just consult with your peers.

* Side note when writing this an idea occurred to me of using the stake in a PoW blockchain to secure a different an alternate blockchain. I have no idea if this has any merit but when writing this, it occurred to me that this might not have have the "PoW" problem.