Cryptography In pricing fuction, what does this sentence mean?

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In pricing fuction, what does this sentence mean? Posted: 28 Jul 2018 06:43 PM PDT In the article 'pricing via processing or combatting junk mail', the original paper that gives the cornerstone of the concept 'proof of work', what does the second option of the following mean? A function f is a pricing function if f is moderately easy to compute; f is not amenable to amortization: given l values m_1, ... , m_l, the amortized cost of computing f(m_1), ... , f(m_l) is comparable to computing f(m_i) for any 1 <= i <= l; given x and y it is easy to determine if y = f(x). submitted by /u/Makeyounod_e [link] [comments]

Question about performing an attack on unprocessed transactions in blockchain. Posted: 28 Jul 2018 01:49 AM PDT This is for the scenario where quantum computers could derive a private key from a public key and hijack an unprocessed transaction during blocktime as described in point 3, page 8 in this paper: https://arxiv.org/pdf/1710.10377.pdf Extra info: some blockchains only have hashes of their pubkey public until a transaction is made. The misconception is that these blockchains are quantum resistant because unhashing, even by a quantum computer would take ages. Where deriving a private key from an unwashed pubkey using Shor's or Grovers algorithm with a quantum computer can be done in a more useful timeframe. BTC can be hacked that way where the private key is derived fast enough during a blocktime as said described in this paper in point 3, page 8: https://arxiv.org/pdf/1710.10377.pdf Another blockchain might have solved that by having a blockchain with instant transactions in First-In-First-Out order, where a pub key is unhashed only when the transaction is made and then becomes instantly useless. Also they use fixed fees, so you wouldn't be able to cut in line and perform a man in the middle attack. (Also FIFO should stop that). The question is: would the chain still be vulnerable for network based attacks? DDoS, BGP routing attacks, NSA Quantum Insert and Eclipse attacks for example? (Or other attacks where you could disrupt the communication between the sender and the miner. Or where you could slow down an "instant" transaction.) For example DDoS the network so the miners can't see the transactions before you get them. Then you crack the key, create your malicious transaction, and push that to the miners. But I would think that this would be impossible because the sender only sends the hashed pubkey. Or am I wrong? Could the transaction itself be delayed in some attack instead of being instant and create an opening that way to have enough time to perform a man in the middle attack? submitted by /u/QRCollector [link] [comments]

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