Schedule
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If you didn’t get full credit for Project 1 because of failure to post something interesting, you can (and should!) redeem yourself and earn full credit by posting an interesting comment by Thursday. It can be on (1) Discussion questions from Project 1 (2) notes from classes, or (3) general forum.
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Quiz: We'll have a short, closed resources quiz in class on Wednesday, 11 February. The point of the quiz is to see how well people are understanding the core ideas we've covered so far (including today).
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Read (by Monday): Chapter 6: The Bitcoin Network, Chapter 7: The Blockchain from Andreas Antonopoulos' book.
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I am away the rest of this week, so will not have office hours on Thursday. (I am, of course, still available by email and course web site.)
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In Monday's class, Nick and Alex will explain what is provided and what you need to do for project 2. You should at least set up your node for project 2 before class Monday (details will be posted tomorrow). You will also have an opportunity to ask questions about anything we have covered so far. If you have questions you want answered, or topics you'd like discussed, you can post them in the comments for these notes (or email me directly).
If you download the slides, they are present though. Hopefully, the player will be fixed someday.
Exploring Blocks
| Label | Bytes | Description |
|---|---|---|
version |
4 | Block version information |
prev_block |
32 | Hash of the previous block |
merkle_root |
32 | Hash of Merkle tree of all transactions |
timestamp |
4 | When block was created (overflows in 2106) |
bits |
4 | Difficulty target used for this block |
nonce |
4 | Nonce found to generate this block |
{
"hash":"000000000000000002b32e242989056214fef31c5aac08ae517840db3e3e7fd2",
"ver":2,
"prev_block":"000000000000000014a97984448f2b3e5b8582ece719be1a1ea7db1d1fce5561",
"mrkl_root":"d634ceec0d9a8b065ad3203555b74877d0476e0b302972be41671a6b92a0a066",
"time":1422830051,
"bits":404399040,
"nonce":527809407,
"n_tx":1511,
"size":760657,
"tx":[
{
"hash":"57db55dadb51ceeee6417af30946f234b2f77613e40586a2c03ce5e3a2be8bbb",
"ver":1,
...
"size":3533,
"in":[
{
"prev_out":{
"hash":"0000000000000000000000000000000000000000000000000000000000000000",
"n":4294967295
}, ...
],
"out":[
{
"value":"1.00076629", ...
},
{
"hash":"675e40df163d5ae4556774b325cdd7b0885d552bf7989d5e24f7039fce315a5b",
...
"in":[
{
"prev_out":{
"hash":"04e9c75d42093094a486a1c898527f4b50e1788fe4fda3ecb2574662b75b6f90",
...
}
],
"out":[
{
"value":"0.00100000",
"scriptPubKey":"OP_DUP OP_HASH160 9e21abc1748a1df63b4016ac313c0f88e557d5fd ..."
},
{
"value":"0.00710182",
"scriptPubKey":"OP_DUP OP_HASH160 e37cd341540dd1e912568ae5b004d62422bd6b38 ..."
}
]
},
...
],
"mrkl_tree":[
"57db55dadb51ceeee6417af30946f234b2f77613e40586a2c03ce5e3a2be8bbb",
"66a3eea4610dfb7d7987ad4fc22392c7964340d21006c1eea4c88174fd660c58",
...
"675e40df163d5ae4556774b325cdd7b0885d552bf7989d5e24f7039fce315a5b",
...
]
}
Merkle Trees
https://github.com/btcsuite/btcd/blob/master/blockchain/merkle.go (some comments removed)
// HashMerkleBranches takes two hashes, treated as the left and right tree
// nodes, and returns the hash of their concatenation.
func HashMerkleBranches(left *btcwire.ShaHash, right *btcwire.ShaHash) *btcwire.ShaHash {
var sha [btcwire.HashSize * 2]byte
copy(sha[:btcwire.HashSize], left.Bytes())
copy(sha[btcwire.HashSize:], right.Bytes())
newSha, _ := btcwire.NewShaHash(btcwire.DoubleSha256(sha[:]))
return newSha
}
func BuildMerkleTreeStore(transactions []*btcutil.Tx) []*btcwire.ShaHash {
nextPoT := nextPowerOfTwo(len(transactions))
arraySize := nextPoT*2 - 1
merkles := make([]*btcwire.ShaHash, arraySize)
// Create the base transaction shas and populate the array with them.
for i, tx := range transactions { merkles[i] = tx.Sha() }
// Start the array offset after the last transaction and adjusted to the
// next power of two.
offset := nextPoT
for i := 0; i < arraySize-1; i += 2 {
switch {
case merkles[i] == nil:
merkles[offset] = nil
case merkles[i+1] == nil:
newSha := HashMerkleBranches(merkles[i], merkles[i])
merkles[offset] = newSha
default:
newSha := HashMerkleBranches(merkles[i], merkles[i+1])
merkles[offset] = newSha
}
offset++
}
return merkles
}
What is needed to verify T2 in Hroot?
What must be recomputed if T3 is replaced?
What must be computed if a new node, T5, is added?
How many SHA-256 hashes must be computed to verify Block 341537?
Comments