Block Chain Foundation (i)

Lecture 1.1 1.2
Author: bao_zijian@163.com Cryptographic Hash Functions property: 1.collision Free Nobody can find X and y Sun that x!=y and H ( x) =h (y) applies: If H (x) =h (y) then x=y. Here h (x) and H (Y) are only 236bits, so it saves space. 2.Hiding given H (x), it is infeasible to find X. 3. Puzzle-Friendly (the nature of the bitcoin needs) if the K is chosen for any n-bit output value Y, it is assumed that a feasible method could not be found if it is less than 2 of n times. Inside find x, guarantee H (k| | x) =y is established, then we call hash function h as a puzzle friendly.
Lecture 1.3 Author: bao_zijian@163.com Hash pointers and authenticated data structures
Key Idea:1. Take any pointer-based data structure 2. Replace Pointers with cryptographic hashes

Modifications to any block would propagate forever
Merkle tree:binary tree with hash pointers




Lecutre 1.4 Author: bao_zijian@163.com Digital signatures
1. (SK, pk): = Genkey (keysize) Sk:secret signing key Pk:public verification key 2.sig: = sign (SK, message) 3.isValid: = Verify (PK, message, SIG) where 1.2.can is randomized algorithms, I understand that 1 this generating key is a random algorithm, sign is also a random algorithm.
Requirements 1.correctness SK, pk = Genkey (keysize) →verify (PK, message, sign (SK, message)) = = True 2.unforgeability (EUF-CMA Securit Y) adversary given PK may adaptively query Oracle for sign (MI) cannot output a valid signature pair (σ, M ') to any new me Ssage m '



Lecture 1.5 Author: bao_zijian@163.com
Public key is a identity anybody can get a identity with genkey collisions statistically negligible to "Speak" as PK, sign using SK Keys are pseudonyms here is a better blog introduction: http://blog.csdn.net/qishuo_java/article/details/48137989

1. First use the random number generator to generate a "private key". In general, this is a 256bits number, with this number can be the corresponding "wallet address" in the bitcoin operation, so must be safely saved.
2. The "Private key" is processed by the SECP256K1 algorithm to generate the "public key". SECP256K1 is an elliptic curve algorithm, which can be counted as "public key" through a known "private key", while "public key" cannot be calculated backwards by "private key" when it is known. This is the basis of the algorithm to guarantee the security of the bit currency.
3. Like SHA256, RIPEMD160 is also a hash algorithm, by which the "public key" can be computed with a "public key hash", which in turn is unworkable.
4. Connect a byte address version number to the "Public key Hash" header (for the PubKey address of the Bitcoin network, this byte is "0" and then it is two times SHA256, and the first 4 bytes of the result are used as the checksum of the "public key hash" to connect to its tail.
5. The last step results are encoded using BASE58 (a custom version of Bitcoin), and the "wallet address" is obtained. For example, 1a1zp1ep5qgefi2dmptftl5slmv7divfna