Massive txs leave bitcoin unsecure for a long time.

[agorism]

Each blockreward is 25BTC=$11,000
It would cost at least $55,000 for someone to unspend a txs that is buried 5 blocks deep.

What if Satoshi decided to move $1,000,0000,000 of coins at once?
It would take 90,909 blocks of confirmations before we could trust the blockchain again, 631 whole days.

Before then, it would still be profitable for satoshi to buy massive amounts of computers, and to build a fake chain from before he spent the money.

If satoshi did build this fake chain, it would undo every transaction.

If someone spends a massive amount of money, it leaves bitcoin in an unsecure state for a long time.

[Peter R]

Your analysis would be more correct for a coin like DOGE 8 months from now, than it is for bitcoin.  

The reason is won't work for bitcoin is that although the market-value of the network's hash rate may be ~$68,000 / hr, there is no way an attacker could lease enough hash-power to carry out your proposed attack for this price.  Instead, an attacker could slowly procure and deploy a sufficient amount of mining hardware to carry out the attack, but this would be several orders of magnitude more expensive (he's now heavily invested in the network like the other big miners).  

I am glad you brought up this point, however, because I think the attack you proposed will be used on DOGE within the next 12 months, as their inflation rate drops to a couple hundred dollars per hour.  Since there is a huge pool of scrypt hashing power that could potentially be rented from people who don't care about DOGE, it would be feasible for an attacker to 51% attack DOGE for a fairly low cost.  If the attacker could establish a large short position prior to the attack, he would be financially motived as well.  

[grue]

I still don't see how a large transaction makes the chain vulnerable. sure, if a transaction is large, it would be smart to wait for more confirmations, but how does the existence of a large transaction affect another transaction's security?

[Cryddit]

He's talking about a transaction that would justify the cost of making an attack. 

But having the money to pay the 'going rate' for hashing power doesn't mean there's that much hashing power available to lease.  You'd start buying hash power, then when the market started to run short the price would start going up.  You'd cost out long before you reached enough hashing power to actually make the 51% attack on the Bitcoin network.

I'm totally with you about Doge though.  Every time they cut their block reward in half (which is often) they'll be cutting their share of hashing power in half.  They'll wind up with not enough to secure the network, because all the miners will be off distributing their hashes up in proportion to the value production. 

[jonald_fyookball]

Each blockreward is 25BTC=$11,000
It would cost at least $55,000 for someone to unspend a txs that is buried 5 blocks deep.

Yeah, it doesn't work that way. 

It's not like the cost of mining equipment is equal to the cost of 1 block,
in any way, shape, or form.

Unless you have 51% of the network, the odds of you building
the longest chain drop exponentially the more blocks you try
to unspend.

[agorism]

Ok, I understand why this attack cannot be done against bitcoin.

Is Dogecoin the only one in danger?
Will we have an exciting day where hundreds of altcoins will die from this attack, one after the other?

[jonald_fyookball]

most altcoins will just die a slow natural death because no one will use them anymore.

[Cryddit]

Is Dogecoin the only one in danger?

No.

The hash power devoted to securing altcoin chains is orders of magnitude smaller than the hash power devoted to bitcoin, and the cost of an attack in general is therefore orders of magnitude smaller.  Doge got a special mention because it was used as an example recently of the economic effects of reward halving on hash power distribution - the author of that paper made the point that every time doge cuts their block subsidy in half the hashing power devoted to securing their blockchain will also be cut in half.  Doge was mined too quick; its block reward is cut in half many times more often than Bitcoin's.  But it isn't the quickest-mined coin out there by any means; just one that's a bit remarkable for the size of its current market cap.  All of the quick-mined coins have this problem, and many of them are already gone.  But that's only the technical side of blockchain safety, and unfortunately that isn't even the main type of risk.

Altcoins, in general, are a cesspool right now.  In fact it would not be too much to say that the *AVERAGE* altcoin is a scam.  Exchanges are openly taking bribes to list altcoins regardless of merit. Some of them are even developing their own altcoins in house for the sole purpose of trading fraud.  Other people are more or less openly accepting payments to hype coins on Reddit, Twitter, etc, then engaging in blatant price manipulation in order to drive prices up on a particular day so scammers can sell their premines at maximum profit. Several coins a week that are doing "crowdfunding" or "IPO" to sell their initial distribution of coins are simply scammers who then disappear with the money. 

If you even consider investing in altcoins, you should first have a definite reason to believe that the one you're investing in isn't a scam.  You should second have legal recourse (meaning, you know AND CAN PROVE exactly who the scammers are and where they live) if it does turn out to be a scam.  If you have trouble following that second rule, it's not because it's an unreasonable rule; it's because scams ARE THE NORM in the altcoin world and scammers will not give you enough information for legal recourse.  While some non-scam coins exist, they are rare exceptions.  Nobody in that business is entitled to the benefit of a doubt.

That's a completely separate issue from chain security w/r/t large (or small) transactions - but once again, if you don't fully understand why a blockchain is (or isn't) secure and what resources are required to attack it - then you don't know enough to even evaluate the security of an altcoin that's operating with different rules, and if you can't evaluate the security of its blockchain, then you shouldn't be investing in it even if it's a non scam.

[bluemeanie1]

Each blockreward is 25BTC=$11,000
It would cost at least $55,000 for someone to unspend a txs that is buried 5 blocks deep.

What if Satoshi decided to move $1,000,0000,000 of coins at once?
It would take 90,909 blocks of confirmations before we could trust the blockchain again, 631 whole days.

Before then, it would still be profitable for satoshi to buy massive amounts of computers, and to build a fake chain from before he spent the money.

If satoshi did build this fake chain, it would undo every transaction.

If someone spends a massive amount of money, it leaves bitcoin in an unsecure state for a long time.

consider also that platforms like Color Coins and Counterparty can potentially make transactions that are worth more than all the Bitcoins in existence!

not to mention that these are TRADES and it's possible to reverse market rallies and collapses.

we're discussing this here:  https://bitcointalk.org/index.php?topic=613643.msg6824824#msg6824824

add to this the fact that hashing power is now a commodity that is brokered and transfered very quickly, and I don't even need to procure hardware, just rent the hashing power for a day or so(thus the estimate to execute an attack is even lower).

-bm

[Marbit]

I'll stick with SHA256 coins that are merge mined with bitcoins, if I'm gonna stick with with any altcoins at all. Stable blockchain is priority #1, and most alt chains are pretty iffy in that regard. (in regards to the discussion on DOGE)

[bluemeanie1]

I'll stick with SHA256 coins that are merge mined with bitcoins, if I'm gonna stick with with any altcoins at all. Stable blockchain is priority #1, and most alt chains are pretty iffy in that regard. (in regards to the discussion on DOGE)

I like your forum signature!  -bm

[jonald_fyookball]

I'll stick with SHA256 coins that are merge mined with bitcoins, if I'm gonna stick with with any altcoins at all. Stable blockchain is priority #1, and most alt chains are pretty iffy in that regard. (in regards to the discussion on DOGE)

I like your forum signature!  -bm

oh...snap.