Kripto 2, Drugi Kol

The correct answer is "Problem autentifikacije je moguce resiti sa digitalnim potpisom" (The problem of authentication can be solved with a digital signature). A digital signature is a cryptographic technique that provides authentication and integrity to digital documents or messages. It ensures that the sender of the message is verified and that the message has not been tampered with during transmission. Therefore, using a digital signature can effectively solve the problem of authentication.

Authentication is a security service that ensures that the message is sent by an authorized person. It verifies the identity of the sender and ensures that the message has not been tampered with during transmission. This helps in preventing unauthorized access and ensures the integrity of the communication.

The correct answer is "Problem autentifikacije je moguce resiti sa digitalnim potpisom." The explanation is that a digital signature is a cryptographic mechanism that provides authentication and integrity of digital documents. It ensures the identity of the sender and verifies that the document has not been tampered with during transmission. Therefore, it is possible to solve the problem of authentication using a digital signature.

Authentication refers to the process of verifying the identity of the sender or the source of a message. In this context, the correct answer states that authentication involves checking whether the received cryptogram (encrypted message) is sent from an authorized person. This means that the authentication process is focused on ensuring that the sender of the message is indeed authorized to send it, thus confirming the authenticity and integrity of the message.

The correct answer is "Verifikovan je digitalni potpis" because the sentence translates to "The digital signature has been verified." This suggests that the verify() method called on the Signature class instance successfully confirmed the authenticity and integrity of the digital signature.

The scenario for secret sharing states that it is not possible to reconstruct the key without one part of the key. This means that each part of the key is essential for reconstructing the original key. Therefore, if one part of the key is missing, it is not possible to reconstruct the complete key.

The question states that the ciphertext (C) is 1000 and the key (K) is 1111. The correct answer, P=0111, can be obtained by performing a bitwise XOR operation between C and K. XORing 1 with 1 gives 0, XORing 0 with 1 gives 1, and XORing 0 with 0 gives 0. Therefore, XORing 1 with 0 gives 1. By applying this operation to each corresponding bit of C and K, we get the result P=0111.

The correct answer is "sesijskog ključa". The explanation for this answer is that a protocol for authentication may require the establishment of a session key. A session key is a temporary encryption key that is generated for a specific session or communication session between two entities. It is used to encrypt and decrypt the data exchanged during that session, ensuring the confidentiality and integrity of the communication. By using a session key, the security of the communication is increased as it is unique to that session and not used for any other session or communication.

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The correct answer is 3 faze. The explanation for this is that the satellite scenario protocol consists of three phases. This means that there are three distinct stages or steps involved in the protocol. The question does not provide any additional information or context to suggest that the number of phases depends on the number of participants in the scenario. Therefore, the answer "3 faze" is the most accurate and logical choice.

The given answer suggests that the process being described in the Java code fragment is the initialization of an initialization vector. An initialization vector is commonly used in encryption algorithms, such as AES, to add randomness and enhance the security of the encryption process. It is used to initialize the state of the encryption algorithm before encrypting or decrypting data.

By calling the getPrivate() method on an instance of KeyPair, the method will return the private key. This means that the getPrivate() method is specifically designed to retrieve and return the private key associated with the KeyPair instance.

The correct answer is Kerberosu. Kerberos is a network authentication protocol that uses timestamps as part of its authentication process. It is commonly used in computer networks to provide secure authentication for users and services. The use of timestamps, or "vremenski pecat" in Serbian, helps to prevent replay attacks by ensuring that authentication requests are only valid for a certain period of time.

The given command "keytool -export -alias RSAsertifikat -keystore /c:\Users\sadamovic\Desktop\skladiste.keystore -file /c:\Users\sadamovic\Desktop\RSAsertifikat.der" is used to export an RSA certificate in DER format. The command specifies the alias of the certificate as "RSAsertifikat" and the keystore file location as "/c:\Users\sadamovic\Desktop\skladiste.keystore". It exports the certificate to a file named "RSAsertifikat.der" at the specified location "/c:\Users\sadamovic\Desktop\".

The correct answer is "za uzajamnu autentifikaciju sa simetricnim kljucem" which translates to "for mutual authentication with symmetric key" in English. This suggests that the protocol design shown in the picture is for a communication process where both parties authenticate each other using a shared symmetric key.

The correct answer is Vajnerov Wire-Tap kanal. The image represents Vajner's Wire-Tap channel, which is a type of communication channel that allows a third party to eavesdrop on the communication between two parties without their knowledge. This channel is often used in cryptography to simulate real-world scenarios and test the security of encryption algorithms.

The correct answer is 3 because the question asks how many phases of the protocol are shown in the picture. Since the answer provided is 3, it implies that there are three distinct phases of the protocol depicted in the image. However, without the image or a more detailed description, it is difficult to provide a comprehensive explanation.

The correct answer is that the system cannot be broken even with unlimited computer resources. This means that no matter how much computational power is available, the encryption algorithm used in the system is so strong that it cannot be cracked or decrypted. This level of security ensures that the system is completely safe and cannot be compromised, making it unconditionally secure.

In the authentication protocol with a symmetric key, Alisa and Bob exchange a symmetric key in advance. This means that they both have the same key, which they can use for encryption and decryption. This allows them to securely communicate by encrypting and decrypting messages using the shared key. Sharing the same symmetric key ensures that only Alisa and Bob can access and understand the encrypted messages.

The given scenario of opening a safe with two keys and launching a rocket requiring three authorizations indicates the concept of "Deljenje tajni" or "Sharing secrets." In this scenario, multiple individuals hold different pieces of information or keys, and their collaboration is necessary to achieve the desired outcome. This concept emphasizes the need for sharing classified information or access to restricted resources among trusted parties to accomplish a specific task or goal.

This answer suggests that the term "bezbednost" refers to security against an adversary who has unlimited time and computational resources. This means that the level of security being discussed is focused on protecting against attacks from an adversary who has the ability to dedicate unlimited resources to breaking the security measures in place.

The correct answer states that protocols for mutual authentication with symmetric keys are not always safe and that there is a possibility of an attack. This implies that while these protocols may provide security in some cases, they are not foolproof and can still be vulnerable to certain attacks.

The correct answer is "Da napadac prima zasumljenu verziju signala legitimnog prijemnika". This means that the only condition for the safe operation of the Vajner Wire-Tap channel is that the attacker receives a noisy version of the legitimate receiver's signal.

The blue dashed horizontal line on the graph represents the boundary of the attacker. This means that any data or actions that lie beyond this boundary are considered to be outside of the attacker's control or influence. It signifies the limit or extent to which the attacker can potentially cause harm or compromise the system's security.

Senon razlikuje dve vrste bezbednosti: računarsku i bezuslovnu.

The correct answer is "Postoji kljuc koji preslikava svaku poruku u bilo koji sifrat sa jednakom verovatnocom." This means that there is a key that can map any message to any cipher with equal probability. In other words, each message has an equal chance of being encrypted into any possible cipher. This ensures that the encryption process is unbiased and random, making it difficult for an attacker to determine the original message based on the cipher.

The question is asking about the characteristics of the codes shown in the picture. The correct answer is "Perfektni sifarski algoritam" which translates to "Perfect cipher algorithm" in English. This suggests that the codes in the picture are an example of a perfect cipher algorithm, which is a type of encryption algorithm that provides perfect secrecy and is unbreakable even with infinite computational power.

The correct answer is "privatni i javni kljuc." This is because the class KeyPair in Java typically represents a pair of cryptographic keys, which consists of both a private key and a public key. These keys are used for various encryption and decryption operations in cryptography.

The correct answer is "Bob autentifikuje Alisu sa simetricnim kljucem". This means that Bob is authenticating Alice using a symmetric key. This implies that Bob and Alice share the same key, and Bob is verifying Alice's identity using this key.

The correct answer is "mogucnost ponovnog slanja" (possibility of replay attacks). A replay attack occurs when an attacker intercepts and maliciously retransmits data that was previously valid. In the context of the given question, it refers to the possibility of an attacker intercepting and resending data, potentially compromising the security of the system. This could lead to unauthorized access or other malicious actions.

The given statement is discussing the requirements for authentication and confidentiality in a cryptographic system. It states that in order to guarantee authentication, the probability of incorrect decryption (PI) must be low, which means that the mutual information between the ciphertext (C) and the key (K) must be high. On the other hand, to ensure absolute confidentiality, it must hold that I(C;M) = 0, which contradicts the requirement for authentication. Therefore, the statement is true because the requirements for authentication and absolute confidentiality are contradictory.

The correct answer is "Protokol za obostranu autentifikaciju koji implementira PFS." This means that the cryptographic protocol shown in the picture is a protocol for mutual authentication that implements Perfect Forward Secrecy (PFS). PFS ensures that even if the long-term secret key is compromised, past sessions remain secure.

The correct answer is "Autentifikacija sa simetricnim kljucem" (Authentication with symmetric key). This is indicated by the image, which suggests that a symmetric key is being used for authentication. Symmetric key authentication involves using the same key for both encrypting and decrypting data, ensuring that the sender and receiver have the same key to authenticate each other.

PFS (Perfect Forward Secrecy) podrazumeva korišćenje sesijskog ključa koji se koristi samo jednom, a zatim trajno uništava. Ovo je važno za obezbeđivanje sigurnosti komunikacije, jer se svaki put kada se uspostavi nova sesija generiše novi ključ koji se ne može rekonstruisati iz prethodnih sesija. Na taj način, čak i ako se jedan ključ kompromituje, prethodne sesije ostaju sigurne. Uništavanje ključeva nakon korišćenja sprečava njihovo eventualno otkrivanje i zloupotrebu.

Cryptographic systems for absolute secrecy cannot provide authentication because authentication involves verifying the identity of the sender or recipient of a message. While cryptographic systems can ensure confidentiality by encrypting the message, they do not have the capability to verify the authenticity of the sender or recipient. Authentication requires additional mechanisms such as digital signatures or certificates to ensure the integrity and authenticity of the communication.

The given command "keytool - export -alias DSAsertifikat -keystore /c:\Users\sadamovic\Desktop\skladiste.keystore -rfc -file /c:\Users\sadamovic\Desktop\DSAsertifikat.b64" exports the DSA certificate in BASE64 format. This means that the DSA certificate will be encoded using the BASE64 encoding scheme, which represents binary data in ASCII format. The exported certificate will be saved in the file named "DSAsertifikat.b64" on the desktop of the user "sadamovic".

In the given protocol for authentication with a timestamp, the correct sequence of steps is to first sign the message, then calculate the timestamp, and finally encrypt the message. This order ensures that the message is securely signed before the timestamp is added and the entire message is encrypted. If the steps were performed in a different order, the security and integrity of the authentication process could be compromised.

The correct answer is "Maksimalna brzina pri kojoj se A I B dogovore o tajnom kljucu S." This means that the maximum speed at which A and B can agree on a secret key S is the correct answer. This suggests that there is a certain speed limit or threshold that A and B need to meet in order to establish a secure secret key. It implies that if their speed is below this maximum limit, they will not be able to successfully agree on the secret key.

DES (Data Encryption Standard) and AES (Advanced Encryption Standard) are both symmetric cryptographic algorithms that can be used for authentication. Symmetric cryptographic functions use the same key for both encryption and decryption, making them suitable for verifying the authenticity of data. DES and AES are widely used and trusted encryption standards, with AES being the more secure and commonly used algorithm in modern cryptographic systems.

Authentication and confidentiality are theoretically incompatible. This means that in theory, it is difficult to achieve both authentication and confidentiality simultaneously. Authentication ensures that the user or entity is who they claim to be, while confidentiality ensures that the information is kept private and secure. In practice, implementing strong authentication measures can sometimes compromise confidentiality, and vice versa. However, this answer suggests that in theory, it is not possible to achieve both authentication and confidentiality without some trade-offs or challenges.

The expression I(M;C)=0 guarantees that the ciphertext does not reveal any information about the plaintext.

In a satellite scenario, the transmission error refers to the error that occurs during the transmission of data from the sender to the receiver, while the attacker's error refers to any error introduced by an attacker trying to disrupt the communication. The correct answer states that the attacker's error is 0, meaning that there is no error introduced by the attacker. This implies that the communication is not compromised by any malicious activity, making the satellite scenario possible.

Satelitski scenarij se koristi za razmenu tajnog ključa preko javnog kanala. Tajni ključ je ključ koji se koristi za enkripciju i dekripciju podataka. Javni kanal je komunikacijski kanal koji je otvoren za sve korisnike i na kojem se mogu razmenjivati podaci. Tajni ključ se šalje preko javnog kanala kako bi se obezbedila sigurna komunikacija između dve strane.

The correct answer is "nije namenjen za autentifikaciju na mreži." This is because TCP protocol is not designed specifically for network authentication purposes. TCP (Transmission Control Protocol) is a reliable transport protocol that ensures the delivery of data packets in a network. It handles the segmentation, reassembly, and flow control of data. However, authentication in a network typically requires protocols like RADIUS or LDAP, which are specifically designed for authentication purposes. TCP does not provide built-in authentication mechanisms.

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Senonov ideal tajnog komuniciranja podrazumeva da pošiljalac koristi True Random Number Generator (TRNG) za generisanje nasumičnih ključeva ili brojeva koje koristi za enkripciju poruke. Ovi nasumični ključevi su potpuno nepredvidivi i neponovljivi. Primalac takođe koristi isti TRNG za generisanje istih ključeva kako bi dešifrovao poruku. Ovaj pristup osigurava visok nivo tajnosti i sigurnosti u komunikaciji između pošiljaoca i primaoca.

The correct answer is "nemoguca ili mit" which translates to "impossible or myth" in English. This suggests that the statement is claiming that proving computer security is either impossible or just a myth. It implies that achieving complete and foolproof security in the realm of computers is extremely challenging, if not unattainable.

In the given protocol, both Alisa and Bob are required to know the password. This is indicated by the statements "Alisa mora da zna lozinku" (Alisa must know the password) and "Bob mora da zna lozinku" (Bob must know the password). Therefore, the correct answer is that both Alisa and Bob must know the password.

Difi-Helman se koristi za implementaciju PFS (Perfect Forward Secrecy) u zastitni protokol. PFS je sigurnosna karakteristika koja osigurava da, čak i ako se privatni ključ kompromituje u budućnosti, prethodne komunikacije ostanu sigurne. Difi-Helman protokol omogućava razmenu tajnih ključeva između dvije strane koje komuniciraju, bez da te ključeve razmjenjuju preko mreže. Na taj način, čak i ako napadač presretne komunikaciju i dobije trenutne ključeve, neće biti u mogućnosti dešifrovati prethodne poruke.

The correct answer states that unconditional security implies that for a given cryptographic system, it can be rigorously proven to have nominated security against an adversary with unlimited time resources. This means that no matter how much time the adversary has, they will not be able to break the security of the system.