Distributed Systems

Question 1

What is the name of the protocol that uses an iterative application of the Diffie-Hellman algorithm for distributed group key management?

Answer 1

The protocol that uses an iterative application of the Diffie-Hellman algorithm for distributed group key management is called the Tree-based Group Diffie-Hellman (TGDH) protocol.

Question 2

What are the advantages of the Needham-Schroeder protocol for dynamic pairwise key establishment?

Answer 2

1.The Needham-Schroeder protocol is simple and efficient for establishing pairwise keys in a distributed system.

2.It provides mutual authentication between the communicating parties.

Question 3

What are the disadvantages of the Needham-Schroeder protocol for dynamic pairwise key establishment?

Answer 3

1.The protocol assumes that the communication channel between the group controller and the users is secure, which may not always be the case.

2.It relies on a trusted group controller for key distribution, which can be a single point of failure.

3.The protocol is vulnerable to replay attacks if timestamps or sequence numbers are not used.

Question 4

What is the difference between a multi-signature and a group signature algorithm?

Answer 4

A multi-signature algorithm requires all or a certain number of users to sign a message, and anyone can verify the signatures and know who the signers are. It is often used in scenarios where joint approval from multiple parties is required.

A group signature algorithm allows any group member to sign a message on behalf of the group, and anyone can verify the signature but cannot identify the signer. It is often used in scenarios where signer anonymity is required.

Question 5

What is the purpose of a proof-of-work in a blockchain-based distributed ledger

Answer 5

The purpose of a proof-of-work in a blockchain-based distributed ledger is to deter denial of service attacks and other service abuses such as spam on a network by requiring some work from the service requester, usually meaning processing time by a computer.

Question 6

How can Shamir’s secret sharing be used to implement a (k,n) threshold signature algorithm?

Answer 6

Shamir’s Secret Sharing can be used to implement a (k,n) threshold signature algorithm in the following way:

*The secret (e.g., a private key) is split into n shares using Shamir’s Secret Sharing.
Each of the n users holds one share.

*To sign a message, each user signs the message with their share of the secret.

*Any k out of n signatures can be combined to produce the original signature.

*The original signature can be verified with the public key corresponding to the secret.

*This way, any k out of n users can jointly sign a message, but any fewer than k users cannot.

Question 7

What is the role of a group controller in the Needham-Schroeder protocol?

Answer 7

In the Needham-Schroeder protocol, the group controller (GC) plays a crucial role. It is responsible for generating and distributing keys to the users. The GC acts as an intermediary, enabling users to establish pairwise keys with each other.

Question 8

How does the tree-based group Diffie-Hellman (TGDH) protocol work?

Answer 8

The Tree-based Group Diffie-Hellman (TGDH) protocol is a decentralized approach to manage keys in distributed systems. It allows users to create a group key using the Diffie-Hellman algorithm iteratively. The users are organized in a binary tree, where each user is a leaf node. Each node in the tree (including the leaf nodes) holds a group key, which is the result of the Diffie-Hellman operation between the keys of its child nodes. When a user wants to join or leave the group, only the keys of the nodes on the path from the user to the root need to be updated.

Question 9

What are the advantages of centralized key management in distributed systems?

Answer 9

Simplicity and efficiency. The group controller can easily distribute keys and handle authentication.

Question 10

What are the disadvantages of centralized key management in distributed systems?

Answer 10

Single point of failure (the group controller), potential bottleneck in large systems, and trust issues (all users must trust the group controller).

Question 11

What are the advantages of decentralized key management in distributed systems?

Answer 11

No single point of failure, better scalability, and does not require trust in a single entity.

Question 12

What are the disadvantages of decentralized key management in distributed systems?

Answer 12

More complex to implement, and key updates (due to users joining or leaving) can be more computationally intensive.

Question 13

What is the purpose of Shamir’s Secret Sharing in the context of distributed systems?

Answer 13

Shamir’s Secret Sharing is a method by which a secret can be divided into parts, giving each participant its own unique part. The unique property of this method is that you need a minimum number of parts to reconstruct the whole secret. In the context of distributed systems, it can be used to implement secure multi-party computations and threshold cryptosystems.

Question 14

How does a blockchain-based distributed ledger ensure the integrity and authenticity of transactions?

Answer 14

Blockchain uses cryptographic hash functions to ensure the integrity of transactions. Each block contains a hash of all its transactions, and each new block contains the hash of the previous block, creating a chain of blocks. This makes it nearly impossible to alter a transaction once it has been added to the blockchain. For authenticity, blockchain uses public-key cryptography. Transactions are signed with the sender’s private key, and anyone can verify the signature with the sender’s public key.

Question 15

What is the role of miners in the operation of a blockchain-based distributed ledger?

Answer 15

Miners play a crucial role in the operation of a blockchain-based distributed ledger. They validate and add new transactions to the blockchain. They do this by solving a complex mathematical problem (proof-of-work), which requires significant computational resources. Once a miner solves the problem, they add the new block of transactions to the blockchain. In return for their work, miners are rewarded with cryptocurrency.

Question 16

How does a multi-signature wallet enhance the security and control of funds in a blockchain-based system?

Answer 16

A multi-signature wallet requires multiple parties to sign a transaction before it can be executed. This adds an extra layer of security because even if one party’s private key is compromised, the attacker cannot execute transactions without the other required signatures. It also provides better control of funds, especially in an organization, as it requires consensus before funds can be spent.

Question 17

What is the difference between a linear secret sharing scheme and a threshold secret sharing scheme?

Answer 17

In a linear secret sharing scheme, all shares are required to reconstruct the secret. In a threshold secret sharing scheme, any subset of shares of a certain size (the threshold) can reconstruct the secret. The latter is more flexible and can tolerate the loss or unavailability of some shares.

Question 18

How can the storage space and bandwidth required for a blockchain-based distributed ledger be optimized?

Answer 18

There are several ways to optimize the storage space and bandwidth required for a blockchain-based distributed ledger1. One way is through “pruning” the blockchain, which involves removing certain parts of the data that are no longer needed (like spent transactions). Another way is through the use of more efficient data structures, like Merkle trees, which can store large amounts of data compactly and securely.

Question 19

What are some applications of group signatures in distributed systems?

Answer 19

Group signatures are useful in any scenario where anonymity is important. For example, they can be used in electronic voting systems to ensure that votes are anonymous but still verifiable. They can also be used in anonymous credential systems, where users can prove membership in a group without revealing their identity. Another application is in vehicular ad hoc networks (VANETs), where vehicles can send anonymous but authenticated messages to each other for traffic safety and efficiency.

Question 20

What operations must be supported for groups in Security of Distributed Systems?

Answer 20

User join, User leave, User eject, Group Merge, Group Partition

Question 21

What are some of the reasons to use distributed security mechanisms?

Answer 21

Secrets are too important to be kept by one user

It is easier to trust many than one user

Robustness is an important factor if multiple users are involved

Question 22

What is the main protection mechanism against eavesdropping?

Answer 22

Encryption

Question 23

What is the name of the protocol that specifies how network traffic is encrypted?

Answer 23

IPSec

Question 24

What is the mathematical function that transforms a message and a key into an encrypted message?

Answer 24

The mathematical function that transforms a message and a key into an encrypted message is called encryption function. It can be denoted as E(m,k), where m is the message, k is the key, and E(m,k) is the encrypted message.

Question 25

What are the two methods that IPsec defines for IP packet authentication and encryption?

Answer 25

The two methods that IPsec defines for IP packet authentication and encryption are IP Authentication Header (AH) and IP Encapsulating Security Payload (ESP). AH provides integrity and authenticity for the IP packet header and payload, while ESP provides confidentiality and optionally integrity and authenticity for the IP packet payload.

Question 26

What is the name of the dynamic key protocol that is used for establishing a pairwise key between two users?

Answer 26

The name of the dynamic key protocol that is used for establishing a pairwise key between two users is Needham-Schroeder protocol. It is a classical protocol that uses symmetric encryption and a trusted third party to generate and distribute keys.

Question 27

What are the roles of the users u1 and u2 and the group controller GC in the Needham-Schroeder protocol?

Answer 27

The roles of the users u1 and u2 and the group controller GC in the protocol are as follows:
- u1 and u2 are the two users who want to communicate securely with each other. They share secret keys with the GC, denoted as k1,GC and k2,GC respectively.
- GC is the group controller or the trusted third party that generates and distributes the pairwise key for u1 and u2, denoted as k12. It also issues tickets that contain the pairwise key and the identity of the users, encrypted with their secret keys.

Question 28

What are the five steps of the message exchange in the Needham Schroeder protocol?

Answer 28

• Step 1: u1 sends a request to GC, containing its identity, the identity of u2, and a nonce nu1. A nonce is a random number that is used to prevent replay attacks.
  
  • Step 2: GC responds to u1, sending back the nonce nu1, the pairwise key k12, the identity of u2, and a ticket for u2 that contains the pairwise key k12 and the identity of u1, encrypted with k2,GC. All these are encrypted with k1,GC.
  • Step 3: u1 decrypts the message from GC, extracts the pairwise key k12 and the ticket for u2, and forwards the ticket and a challenge to u2. The challenge is the nonce nu1 encrypted with k12.
  • Step 4: u2 decrypts the ticket, extracts the pairwise key k12 and the identity of u1, and verifies the challenge by decrypting it with k12 and comparing it with nu1. Then u2 sends back a response to u1, containing the decremented nonce nu1-1 and a new nonce nu2, encrypted with k12.
  • Step 5: u1 decrypts the response from u2, verifies the decremented nonce nu1-1, and sends back the decremented nonce nu2-1, encrypted with k12.

Question 29

What are some of the disadvantages of the Needham-Schroeder protocol?

Answer 29

Some of the disadvantages of the Needham-Schroeder protocol are:
- All users have to trust the GC, which may not be desirable or feasible in some scenarios.
- The GC is a single point of failure, which means that if it is compromised or unavailable, the whole system is vulnerable or disrupted
-The protocol does not support handling of network separation and fusion, which means that it cannot cope with dynamic changes in the network topology or group membership⁵[5].
- The protocol has a limited scalability, which means that it requires a large number of pairwise keys and messages for a large group of users

Question 30

What is the term that describes the trust relationship between the users and the GC?

Answer 30

The term that describes the trust relationship between the users and the GC is trust assumption. It means that the users assume that the GC is honest and reliable, and that it will not reveal or misuse their keys or identities.

Question 31

What is the term that describes the point in a system that can cause the whole system to fail?

Answer 31

The term that describes the point in a system that can cause the whole system to fail is single point of failure. It means that the system depends on a single component or entity, and that if it fails, the system cannot function properly or at all

Question 32

How can efficient confidentiality in distributed systems be achieved by using a shared group key?

Answer 32

Efficient confidentiality in distributed systems can be achieved by using a shared group key for the encryption E(m,k), where m is the message, k is the group key, and E(m,k) is the encrypted message. This way, only one key is needed for the whole group, instead of multiple pairwise keys

Question 33

What is the condition that must be satisfied for providing the group key to the users?

Answer 33

The condition that must be satisfied for providing the group key to the users is that the users must be
authorized. It means that they must have the right or permission to join the group and access the group key and the encrypted messages.

Question 34

What is the term that describes the process of altering the group key in dynamic groups?

Answer 34

The term that describes the process of altering the group key in dynamic groups is rekeying. It means that the group key is changed or updated whenever a user joins or leaves the group, in order to maintain the security requirements of the group key

Question 35

What are the four security requirements that must be satisfied by a group key?

Answer 35

• The four security requirements that must be satisfied by a group key are:
  
  • Key secrecy: Only authorized users receive the group key, and no unauthorized users can obtain or derive the group key.
  • Forward secrecy: Users who join the group after the group key is established do not receive any old group key or any encrypted messages that were sent before they joined the group.
  • Backward secrecy: Users who leave the group do not receive any new group key or any encrypted messages that are sent after they leave the group.
  • Key independence: The group key is independent of any previous or future group keys, and no group key can be derived from another group key.

Question 36

What are the terms that describe the situations where a user joins or leaves the group?

Answer 36

• The terms that describe the situations where a user joins or leaves the group are join operation and leave operation respectively. They are the membership operations that affect the group composition and the group key.

Question 37

What are the terms that describe the situations where a user receives no old or new group key?

Answer 37

• The terms that describe the situations where a user receives no old or new group key are forward secrecy and backward secrecy respectively. They are the security properties that prevent a user from accessing the encrypted messages that are not intended for them.

Question 38

What is the main concept of distributed group key management?

Answer 38

The main concept of distributed group key management is that every user contributes to the session key for encryption, and the key establishment and update mechanisms are based on an iterative application of the Diffie-Hellman algorithm. This way, the group key is generated and distributed without a single point of failure or a trusted third party.

Question 39

What is the name of the algorithm that is used for the key establishment and update mechanisms in group signature (tree based)?

Answer 39

• The name of the algorithm that is used for the key establishment and update mechanisms is Tree-based Group Diffie-Hellman (TGDH) protocol. It is a distributed group key management protocol that arranges the users in a tree structure and uses the Diffie-Hellman algorithm to generate and update the group key.

Question 40

What are some of the advantages and disadvantages of distributed group key management?

Answer 40

• Some of the advantages and disadvantages of distributed group key management are:
  
  • Advantages:
    
    • It is easier to trust many users than one GC, as the users have more control and transparency over the group key.
    • The key establishment is done without a single point of failure, as the users do not depend on a single entity or component for the group key.
    • The mechanisms can handle network partition and merge, as the users can adapt to the changes in the network topology or group membership.
  • Disadvantages:
    
    • Difficult key establishment in networks with high packet losses, as the users may not receive or send the necessary messages for the group key.
    • High communication and computation overhead, as the users have to exchange and process more messages and keys for the group key.

Question 41

What is the main goal of the Diffie-Hellman algorithm?

Answer 41

The main goal of the Diffie-Hellman algorithm is to generate a shared secret key over public channels, without revealing the key to any eavesdroppers or attackers.

Question 42

What are the mathematical elements that are used in the algorithm?

Answer 42

The mathematical elements that are used in the algorithm are:
- ℤp: A group with multiplication modulo p as the operation, where p is a large prime number and * denotes the multiplication operator.
- g: A generator of ℤp, which means that every element of ℤp can be obtained by raising g to some power modulo p.
- k1 and k2: The secret keys of the users u1 and u2, which are randomly chosen from ℤp.
- bk1 and bk2: The blind keys of the users u1 and u2, which are calculated by raising g to the power of k1 and k2 modulo p, respectively.
- k12: The shared secret key of the users u1 and u2, which is calculated by raising the blind key of one user to the power of the secret key of the other user modulo p, respectively.

Question 43

What are the names of the keys that are generated and exchanged by the users in the algorithm? Blind Key Sharing

Answer 43

• The names of the keys that are generated and exchanged by the users in the algorithm are:
  
  • The secret keys k1 and k2, which are generated by the users u1 and u2, and are not exchanged or revealed to anyone.
  • The blind keys bk1 and bk2, which are generated by the users u1 and u2, and are exchanged between them over public channels.
  • The shared secret key k12, which is generated by the users u1 and u2, and is not exchanged or revealed to anyone.

Question 44

How are the users arranged in a tree in the TGDH protocol?

Answer 44

The users are arranged in a tree according to the hierarchical structure of the group, where each node represents a user or a subgroup of users

Question 45

What is the name of the user that is selected for handling the membership operation? In TGDH

Answer 45

The user that is selected for handling the membership operation is called the sponsor. The sponsor is usually the closest user to the new or leaving user in the tree.

Question 46

What is the name of the key that is used for application data encryption? TGDG

Answer 46

The key that is used for application data encryption is called the root key. The root key is derived from the keys of all the users in the group.

Question 47

What are the four steps of the join operation in the TGDH protocol?

Answer 47

The four steps of the join operation in the TGDH protocol are:

Handshake: The new user sends a message to the sponsor with its public key and blind key.
Group key calculation: The sponsor and the other users update their keys and blind keys according to the new user’s information.
Update: The sponsor sends a message to the other users with the new user’s information and the updated tree structure.
Verification: The new user verifies that it has received the correct root key from the sponsor.

Question 48

What are the three steps of the leave operation in the TGDH protocol?

Answer 48

The three steps of the leave operation in the TGDH protocol are:

Leave: The leaving user sends a message to the sponsor with its public key and blind key.
Group key calculation: The sponsor and the other users update their keys and blind keys according to the leaving user’s information.
Update: The sponsor sends a message to the other users with the leaving user’s information and the updated tree structure.

Question 49

What are the two situations that can cause network fusion or separation?

Answer 49

Network fusion: When two or more groups of users come into communication range and decide to merge their groups.
Network separation: When one or more users lose communication with the rest of the group and form a new group.

Question 50

What is the name of the technique that is used to support network fusion?

Answer 50

The name of the technique that is used to support network fusion is key tree merge. This technique involves creating a new common root node for the merged groups and adjusting the keys and blind keys accordingly.

Question 51

What is the name of the technique that is used to support network separation?

Answer 51

The name of the technique that is used to support network separation is key tree split. This technique involves removing the nodes that are no longer in the group and adjusting the keys and blind keys accordingly.

Question 52

What is the main protection mechanism against content modifications?

Answer 52

The main protection mechanism against content modifications is integrity Protection. Integrity protection ensures that data is not altered in transit and that it arrives at the receiving party exactly as it was sent.

Question 53

What are the two types of secret sharing that are discussed in this chapter?

Answer 53

The two types of secret sharing discussed in this chapter are linear secret sharing and threshold secret sharing.

Question 54

What is the main purpose of secret sharing?

Answer 54

The main purpose of secret sharing is to protect a secret by dividing it into multiple parts and distributing them among a group of participants. No subset of participants can reconstruct the secret unless they combine a certain number of parts.

Question 55

What is the difference between linear secret sharing and threshold secret sharing?

Answer 55

Linear secret sharing requires all parts to reconstruct the secret, while threshold secret sharing allows the secret to be reconstructed from a subset of parts.

Question 56

Can you give an example of a situation where secret sharing would be useful?

Answer 56

An example of a situation where secret sharing would be useful is in a distributed system where a group of servers need to store a sensitive piece of information, such as an encryption key, but we don’t want any single server to have access to the whole key.

Question 57

How does linear secret sharing work?

Answer 57

In linear secret sharing, a secret is divided into parts in such a way that all parts are required to reconstruct the secret. Each part does not provide any information about the secret unless combined with all other parts.

Question 58

What is the role of the dealer in linear secret sharing?

Answer 58

The dealer in linear secret sharing is the entity that initially possesses the secret and divides it into parts.

Question 59

What is the role of the users in linear secret sharing?

Answer 59

The users in linear secret sharing are the entities that each receive a part of the secret from the dealer.

Question 60

What is collaborative authentication?

Answer 60

Collaborative authentication is a process where multiple entities work together to authenticate an action. It is often used to add an extra layer of security for sensitive operations.

Question 61

How does collaborative authentication enhance the security of a system?

Answer 61

Collaborative authentication enhances the security of a system by ensuring that no single entity can authenticate an action on their own, which reduces the risk of fraudulent activities.

Question 62

Can you give an example of a system that uses collaborative authentication?

Answer 62

An example of a system that uses collaborative authentication is a multi-signature cryptocurrency wallet, where a transaction must be signed by multiple parties before it can be executed.

Question 63

How does an e-voting system ensure the integrity and authenticity of votes?

Answer 63

An e-voting system ensures the integrity and authenticity of votes by using cryptographic techniques. For example, each vote could be encrypted with the voter’s private key, allowing anyone to verify the vote with the voter’s public key but preventing anyone from altering the vote.

Question 64

Can you give an example of an e-voting system that uses secret sharing?

Answer 64

An example of an e-voting system that uses secret sharing is a system where the decryption key for the votes is shared among a group of authorities. Each authority gets a part of the key, and a certain number of them must work together to decrypt the votes. This ensures that no single authority can decrypt the votes on their own.

Question 65

What is a blind signature?

Answer 65

A blind signature is a cryptographic technique that allows a user to obtain a signature from an authority without revealing the content of the message to the authority.

Question 66

How does a blind signature enhance the privacy of a system?

Answer 66

A blind signature enhances the privacy of a system by allowing the user to prove the authenticity of a message without disclosing its content or identity to the authority or anyone else.

Question 67

Can you give an example of a system that uses blind signatures?

Answer 67

An example of a system that uses blind signatures is an electronic voting system, where the voter can obtain a signature from the election authority on a ballot without revealing the vote or the identity of the voter

Question 68

How does an e-voting system use linear secret sharing and blind signatures?

Answer 68

An e-voting system uses linear secret sharing and blind signatures to provide confidentiality and integrity of the votes. The election authority shares the secret signature key among several authorities using linear secret sharing. The voter blinds the vote with a random number and obtains a signature from each authority using blind signatures. The voter then unblinds the signature and sends the vote and the signature to the authorities for verification and counting.

Question 69

What is the role of the voter in this system?

Answer 69

The role of the voter in this system is to choose a vote, blind it, obtain signatures from the authorities, unblind the signature, and send the vote and the signature to the authorities.

Question 70

What is the role of the authorities in e vote system?

Answer 70

The role of the authorities in this system is to generate and share the secret signature key, sign the blinded votes, verify and count the votes, and reveal the identity of the voter if needed.

Question 71

What is threshold secret sharing?

Answer 71

Threshold secret sharing is a cryptographic technique that allows a dealer to share a secret among a group of users such that any subset of k or more users can reconstruct the secret, but any subset of less than k users cannot.

Question 72

How does threshold secret sharing work?

Answer 72

Threshold secret sharing works by the dealer choosing a polynomial of degree k-1 with the secret as the constant term and giving each user a point on the polynomial as a share. The users can then use interpolation to recover the secret from k or more shares.

Question 73

What is the role of the dealer in threshold secret sharing?

Answer 73

The role of the dealer in threshold secret sharing is to generate and distribute the shares of the secret to the users.

Question 74

How can a secret be reconstructed from a subset of shares in threshold secret sharing?

Answer 74

A secret can be reconstructed from a subset of shares in threshold secret sharing by using Lagrange interpolation, which is a method of finding a polynomial that passes through a given set of points. The users can then evaluate the polynomial at zero to obtain the secret.

Question 75

What is the role of the users in threshold secret sharing?

Answer 75

The role of the users in threshold secret sharing is to keep their shares secret and cooperate with other users to reconstruct the secret when needed.

Question 76

Can you give an example of a situation where threshold secret sharing would be useful?

Answer 76

An example of a situation where threshold secret sharing would be useful is a distributed signature scheme, where a group of users can jointly sign a message using a shared secret key without revealing the key to anyone.

Question 77

What is DNSSEC?

Answer 77

DNSSEC is the Domain Name System with security features, which associates information such as IP addresses with domain names and provides authentication and integrity of the information.

Question 78

How does DNSSEC use threshold signatures?

Answer 78

DNSSEC uses threshold signatures to protect the secret signature key for the root zone, which is the top level of the DNS hierarchy. The key is split into several pieces and distributed among different entities using threshold secret sharing. Signatures are possible with a certain number of pieces using a threshold signature algorithm.

Question 79

Can you give an example of a DNSSEC operation that uses threshold signatures?

Answer 79

An example of a DNSSEC operation that uses threshold signatures is the signing of the root zone file, which contains the information about the top-level domains. The entities that hold the pieces of the root key collaborate to generate a signature on the root zone file using a threshold signature algorithm.

Question 80

What is the main difference between linear secret sharing and threshold secret sharing?

Answer 80

The main difference between linear secret sharing and threshold secret sharing is that linear secret sharing requires the cooperation of all users to reconstruct the secret, while threshold secret sharing allows any subset of k or more users to reconstruct the secret.

Question 81

Can you give an example of a system that uses both secret sharing and blind signatures?

Answer 81

An example of a system that uses both secret sharing and blind signatures is an electronic cash system, where the user can obtain digital coins from a bank using blind signatures and spend them anonymously using secret sharing.

Question 82

What is the main advantage of using distributed ledger technology to document transactions in a group with no trusted third party?

Answer 82

The main advantage of using distributed ledger technology to document transactions in a group with no trusted third party is that it provides transparency, security, and immutability of the transaction history without relying on a central authority or intermediary.

Question 83

What is the name of the technique that links blocks by SHA256 hashes in a distributed ledger?

Answer 83

The name of the technique that links blocks by SHA256 hashes in a distributed ledger is blockchain. Each block contains the hash of the previous block, creating a chain of blocks that can be traced back to the genesis block.

Question 84

What is the term for the verification of transactions in a distributed ledger?

Answer 84

The term for the verification of transactions in a distributed ledger is consensus. Consensus is the mechanism that ensures that all nodes in the network agree on the same state of the ledger and follow the same rules.

Question 85

What are the two types of actors involved in the operation of a blockchain-based distributed ledger?

Answer 85

The two types of actors involved in the operation of a blockchain-based distributed ledger are users and miners. Users are the ones who initiate and broadcast transactions, while miners are the nodes with large computing capacity that create and validate blocks.

Question 86

What is the name of the process that miners perform to find a proof-of-work for a candidate block?

Answer 86

The name of the process that miners perform to find a proof-of-work for a candidate block is mining. Mining is the process of solving a cryptographic puzzle that requires a lot of computational power and random guessing. The first miner who finds a valid solution broadcasts the block to the network and receives a reward.

Question 87

What is the criterion that nodes use to accept the valid version of the ledger in case of branching?

Answer 87

The criterion that nodes use to accept the valid version of the ledger in case of branching is the longest chain rule. The longest chain rule states that the valid version of the ledger is the one that has the most accumulated proof-of-work, or the most blocks. Nodes discard any shorter or conflicting branches and extend the longest chain with new blocks.

Question 88

What is the name of the consensus mechanism that requires miners to solve a cryptographic puzzle to create a valid block?

Answer 88

The name of the consensus mechanism that requires miners to solve a cryptographic puzzle to create a valid block is Proof-of-Work (PoW). This mechanism ensures that only blocks that have a certain level of difficulty are accepted by the network.

Question 89

What is the main parameter that determines the difficulty of finding a proof-of-work?

Answer 89

The main parameter that determines the difficulty of finding a proof-of-work is the target value. The target value is a number that the hash of the block must be lower than in order to be valid. The lower the target value, the harder it is to find a hash that satisfies it.

Question 90

What is the advantage of using a nonce as a random factor in the proof-of-work calculation?

Answer 90

The advantage of using a nonce as a random factor in the proof-of-work calculation is that it allows the miner to vary the input and try different combinations until they find a hash that meets the target value. The nonce is a number that is added to the block header and can be changed by the miner.

Question 91

What is the name of the phenomenon that occurs when two miners find two valid blocks at the same time?

Answer 91

The name of the phenomenon that occurs when two miners find two valid blocks at the same time is branching or forking. This happens when the network is not synchronized and different nodes have different versions of the ledger.

Question 92

What is the rule that nodes follow to resolve the branching of the ledger?

Answer 92

The rule that nodes follow to resolve the branching of the ledger is to accept the longest chain as the valid version. The longest chain represents the most amount of work that has been done by the network and is therefore more likely to be correct.

Question 93

What happens to the transactions that are included in the discarded branch of the ledger?

Answer 93

The transactions that are included in the discarded branch of the ledger are orphaned or stale. These transactions are not confirmed and may be included in future blocks if they are still valid.

Question 94

What is the name of the (crypto-)currency that is based on a blockchain-based public distributed ledger?

Answer 94

The name of the (crypto-)currency that is based on a blockchain-based public distributed ledger is Bitcoin2. Bitcoin is the first and most popular decentralized digital currency that allows peer-to-peer transactions without intermediaries.

Question 95

What is the name of the program that is needed to send and receive bitcoins?

Answer 95

The name of the program that is needed to send and receive bitcoins is a wallet. A wallet is a software that manages the user’s private and public keys, generates bitcoin addresses, and signs and verifies transactions.

Question 96

What is the name of the hash function that is used to generate bitcoin addresses from public keys?

Answer 96

The name of the hash function that is used to generate bitcoin addresses from public keys is SHA256. SHA256 is a secure hash algorithm that produces a 256-bit output from any input. Bitcoin addresses are derived from public keys by applying SHA256 twice and adding a checksum and a prefix.

Question 97

What are the two components of a transaction in bitcoin?

Answer 97

The two components of a transaction in bitcoin are inputs and outputs. Inputs are former outputs that are being consumed, and outputs are the creation of new coins and the transfer of coins to other addresses.

Question 98

What is the name of the data structure that is used to store transactions in a block in an efficient way?

Answer 98

The data structure that is used to store transactions in a block in an efficient way is called a Merkle hash tree. It is a binary tree where each leaf node contains the hash of a transaction, and each non-leaf node contains the hash of the concatenation of its children. The root hash of the tree is included in the block header and serves as a summary of all the transactions in the block.

Question 99

What is the name of the operation that can be performed to reduce the storage space of old transactions without affecting the rest of the tree or changing the hashes?

Answer 99

The operation that can be performed to reduce the storage space of old transactions without affecting the rest of the tree or changing the hashes is called pruning2. It involves deleting the leaf nodes that contain the transactions that have been spent and are no longer needed, and replacing their parent nodes with their sibling nodes. This way, the tree height is reduced and the storage space is saved, while the root hash remains the same.

Question 100

What is the name of the type of wallet that requires multiple users to collaboratively control funds?

Answer 100

The name of the type of wallet that requires multiple users to collaboratively control funds is a multi-signature wallet. It is a wallet that has multiple public keys associated with it, and requires a certain number of signatures (e.g. 2 out of 3) from the corresponding private keys to spend the coins in the wallet.

Question 101

What is the name of the algorithm that can be used to share a secret signature key among the cosigners of a multi-signature wallet?

Answer 101

The name of the algorithm that can be used to share a secret signature key among the cosigners of a multi-signature wallet is Shamir’s Secret Sharing. It is a (k, n)-threshold algorithm that splits a secret into n shares, such that any k of them can reconstruct the secret, but any k-1 of them cannot. The secret can be the private key of the multi-signature wallet, and the shares can be distributed among the cosigners.

Question 102

What is the name of the plugin that can be used to electronically exchange partially signed transactions among the cosigners of a multi-signature wallet?

Answer 102

The name of the plugin that can be used to electronically exchange partially signed transactions among the cosigners of a multi-signature wallet is Cosigner Pool Plugin. It is a plugin for the Electrum wallet that allows the cosigners to communicate with each other via a server and send their partial signatures to complete a transaction.

Question 103

What is the name of the type of signature algorithm that enables a user to sign a message on behalf of a group?

Answer 103

The name of the type of signature algorithm that enables a user to sign a message on behalf of a group is a group signature. It is a signature scheme that allows a member of a group to sign a message in such a way that the verifier can only tell that the signature comes from a member of the group, but not which one. The signer’s identity can be hidden or revealed depending on the context and the policy of the group.

Question 104

What is the name of the technique that allows a user to blind a message with a random number before sending it to an authority for signing?

Answer 104

The name of the technique that allows a user to blind a message with a random number before sending it to an authority for signing is a blind signature. It is a signature scheme that allows a user to obtain a valid signature from an authority without revealing the content of the message to the authority. The user blinds the message with a random factor, sends it to the authority, receives the signature of the blinded message, and then unblinds it to get the signature of the original message.

Question 105

What is the name of the algorithm that can be used to reveal the identity of the signer in a group signature?

Answer 105

The name of the algorithm that can be used to reveal the identity of the signer in a group signature is Elgamal Signature algorithm with random contribution from a Group Controller5. It is a group signature scheme that uses the Elgamal public key cryptosystem and a Group Controller that provides a random contribution to each signature. The Group Controller can also reveal the identity of the signer by disclosing the random contribution and the corresponding public key.

Question 106

What is the main challenge of documenting transactions in a group with no trusted third party?

Answer 106

The main challenge of documenting transactions in a group with no trusted third party is achieving consensus1. In a distributed system, all nodes must agree on the validity and order of transactions. This is difficult because each node has its own copy of the transaction history and can have different views of which transactions have occurred. To solve this problem, blockchain uses a consensus mechanism such as Proof-of-Work (PoW) or Proof-of-Stake (PoS) to ensure that all nodes agree on the same transaction history.

Question 107

What are the six steps involved in the operation of a blockchain-based distributed ledger?

Answer 107

The six steps involved in the operation of a blockchain-based distributed ledger are:2

Transaction: Users send each other digital tokens where the transactions are broadcasted to all nodes.
Block: Transactions are bundled into a block and miners verify them.
Proof-of-Work: Miners compete to solve a mathematical puzzle, which requires computational resources.
Validation: Once a miner solves the puzzle, its solution is sent to all nodes for validation.
Consensus: If a majority of nodes agree that the solution is correct, the block is added to the ledger.
Reward: The successful miner is rewarded with tokens (e.g., bitcoins).

Question 108

What is the name of the decentralized platform that runs smart contracts based on a blockchain-based ledger?

Answer 108

The name of the decentralized platform that runs smart contracts based on a blockchain-based ledger is Ethereum. Ethereum allows developers to build and deploy smart contracts, which are self-executing contracts with the terms of the agreement directly written into code. These smart contracts run on the Ethereum Virtual Machine (EVM), ensuring they benefit from the security and decentralized nature of the Ethereum blockchain.