Chapter A2 Flashcards
Permissionless blockchains are…
Public and
Slow
Security issues of the Bitcoin blockchain include…
Syblic attack and
51% attack
What is a Sybil attack?
With Bitcoin, because identities are based on anonymous public
keys, a user can run multiple nodes and have many accounts. The proof of work
mechanism is essential to prevent users from taking advantage of this - their
voice in the system is proportional to their computational power.
What is a 51% attack?
Because the consensus mechanism “longest chain adoption” is
effectively a majority vote, an adversary controlling 51% of the computation power
of the system can subvert the protocol, even allow double-spend. This is
considered an unlikely scenario for a sufficiently widely-adopted protocol like
Bitcoin.
The ideal properties of cryptographic hash function include the following characteristics:
- Deterministic: always same output hash for the same input
- Fast: quick to obtain the hash value
- Secure: hard to find an input that will generate a given ouput hash
- Discontinuous: a small change in input should change hash substantially
- Low Collision: hard to find two inputs that give the same output hash
Distributed Ledger Technology is a type of immutable database to record transactions in chronological order (typically, in the form of a blockchain), that is…
shared
replicated
synchronized
A _____ is a set of steps that are taken by most or all nodes in a blockchain to agree on a proposed state or value.
consensus mechanism
The ______ states that any distributed system cannot have consistency, availability, and partition tolerance simultaneously.
CAP theorem
Proof of Work, Proof of Stake and Proof of Capacity are examples of
consensus algorithms
What is POW (Proof of Work)?
consensus mechanism relies on proof that
adequate computational resources have been spent before proposing a value for
acceptance by the network.
What is POS (Proof of Stake)?
algorithm works on the idea that a node or user has an
adequate stake in the system; that is, the user has invested enough in the system
so that any malicious attempt by that user would outweigh the benefits of
performing such an attack on the network.
What is POC (Proof of Capacity)?
scheme uses hard disk space as a resource to mine
the blocks.
Via _____ coins can be moved from one blockchain to another and moved back again.
sidechains or
“pegged” sidechains
Any application or database that is shared by the public is a _____
shared ledger
True/False: The primary challenge of distributed systems is the coordination between nodes and fault tolerance.
True
