CS251P - Committing to data (11/02/2015)

CS251P - Committing to data (11/02/2015) - Questions

Please complete these questions for the "Committing to data in the blockchain" lecture: https://docs.google.com/document/d/1xwpMZkDTz8u9O6Q-w3ERsss51S01CP_OyDr3ULjgu8U/edit#

Which two of these are the most significant problems in general with storing non-pubkey data in P2PKH transactions (like Dan Kaminsky did)? *

You have to pay a transaction fee

It worsens the performance of Bitcoin full nodes during validation

Your data can be changed because of transaction malleability

The bitcoin spent by the process Kaminsky used are lost forever

You're limited to 20 bytes

Required

What is a problem with storing data in the blockchain using OP_RETURN? *

It can be censored by miners

It has to use an opaque hash, so nobody can read the data

Bitcoin consensus rules require than 1 out of every 100 OP_RETURN outputs be rickrolls

You're limited to the max data push size, 75 bytes

You have to pay a transaction fee

In the case of paying to contracts or sidechains, why don't contract hashes increase the size of the blockchain? *

Because they merge their data into data already on the blockchain

Because they don't actually store any data on the blockchain

Because you would be paying for that contract, or depositing to that sidechain, anyway and contract hashes don't take up any extra bytes in your transaction

Because they use P2SH transactions, in which all the data is covered by a hash

Because the data is stored on the Bitcoin elliptic curve, which is external to the blockchain

Which two of these are reasonable and considerate uses of the methods discussed today? *

Storing ASCII text in a P2PKH transaction

Storing data you need other people to retrieve in an OP_RETURN output

Storing hashes of documents in OP_RETURN outputs

Storing hashes of documents in pubkeys using contract hashes

Violating copyright on the blockchain in a way that is detectable by miners and governments

Required

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