Kripto 2

The correct answer includes two options: "Simetricni" (Symmetric) and "Asimetricni" (Asymmetric). This suggests that "Sifarski sistemi" (Number systems) can be either symmetric or asymmetric.

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The correct answer is "Simetricne sisteme,Asimetricne sisteme". The question is asking for the basic division of cipher systems according to the type of key. The answer states that the division includes symmetric systems and asymmetric systems. Symmetric systems use the same key for both encryption and decryption, while asymmetric systems use different keys for encryption and decryption.

The correct answer is "Napad tipa covek u sredini" (Man-in-the-middle attack). The Diffie-Hellman algorithm for establishing a shared secret is vulnerable to this type of attack. In a man-in-the-middle attack, an attacker intercepts the communication between two parties and impersonates each party to the other, allowing them to intercept and modify the messages exchanged. This can compromise the security of the shared secret established through the Diffie-Hellman algorithm.

The given expression "52 (mod 17)" represents the remainder when 52 is divided by 17. To find this remainder, we divide 52 by 17 and see what is left over. In this case, 52 divided by 17 is 3 with a remainder of 1. Therefore, the correct answer is 1.

The correct answer is "Mala promena na ulazu izazvace veliku promenu na izlazu." This statement describes the Lavinski effect, which is defined as a small change at the input causing a large change at the output. This phenomenon is commonly observed in amplifiers and electronic circuits, where a small input signal can result in a much larger output signal.

The correct answer is 1000 times. This means that RSA is 1000 times slower than AES. RSA is a public-key encryption algorithm that is primarily used for secure data transmission, while AES is a symmetric encryption algorithm that is commonly used for encrypting data at rest. The slower speed of RSA is due to its more complex mathematical operations, such as modular exponentiation, which require more computational resources and time compared to the simpler operations used in AES.

The correct answer is "Runda". In block ciphers, the encryption process is divided into multiple rounds, where each round applies a specific set of operations to the input data. These operations typically include substitution, permutation, and mixing of the data. Therefore, the term "runda" refers to the specific step or iteration within the encryption process of a block cipher.

The correct answer is the set of key lengths used in PKI systems: 1024, 2048, 4096. These key lengths are commonly used in PKI systems to ensure secure encryption and authentication. The larger the key length, the stronger the encryption and the more secure the system. Therefore, using longer key lengths such as 1024, 2048, and 4096 provides a higher level of security in PKI systems.

The given answer states that the key (K) is calculated as Bi raised to the power of a, modulo p. This means that Alisa takes the value received from Bob (Bi) and raises it to the power of her own secret value (a), and then takes the remainder when divided by p. This calculation allows Alisa to generate a shared key with Bob using the Diffie-Hellman key exchange algorithm.

The given expression is (25*13)(mod 6). First, we multiply 25 and 13, which gives us 325. Then, we take the modulus of 325 with 6. The modulus operation gives us the remainder when 325 is divided by 6. In this case, 325 divided by 6 gives a remainder of 1. Therefore, the correct answer is 1.

Double DES (2DES) uses a key length of 112 bits. Double DES is a variant of the Data Encryption Standard (DES) algorithm that applies DES encryption twice to increase security. In Double DES, two 56-bit keys are used consecutively. Since each key is 56 bits long, the total key length becomes 112 bits. This increases the complexity of the encryption process and makes it more difficult for attackers to crack the encryption.

Autentifikacija je neophodna kako bi se sprečio napad na DH algoritam. Autentifikacija je proces provere identiteta korisnika ili uređaja, čime se osigurava da samo legitimni korisnici imaju pristup sistemu. U kontekstu DH algoritma, autentifikacija se koristi kako bi se osiguralo da komunicirajuće strane zaista jesu one koje tvrde da jesu, čime se sprečava prisustvo neovlašćenih korisnika koji bi mogli pokušati da izvrše napad na algoritam.

RSA algoritam koristi javni ključ za enkripciju podataka i privatni ključ za dekripciju podataka. Javni ključ je dostupan svima i koristi se za enkripciju podataka koje samo vlasnik privatnog ključa može dekriptovati. Privatni ključ se čuva tajno i koristi se za dekripciju podataka koje su enkriptovane javnim ključem. Ova kombinacija javnog i privatnog ključa omogućava sigurnu razmenu podataka između korisnika RSA algoritma.

The length of a block in the AES algorithm can be 128 bits, 192 bits, or 256 bits. This means that the AES algorithm can process data in blocks of these sizes. The choice of block size depends on the specific application and security requirements. A larger block size generally provides stronger security but may also result in slower processing speed.

In a brute-force attack, all keys are equally likely to be the correct key. This means that the attacker has to try all possible keys until they find the correct one. This is because the brute-force attack method involves systematically trying every possible combination until the correct key is found. Therefore, there is no bias towards any specific key in a brute-force attack.

CBC (Cipher Block Chaining) is a block cipher mode of operation that provides confidentiality and message authentication. In CBC mode, each plaintext block is XORed with the previous ciphertext block before encryption. This ensures that even if two plaintext blocks are identical, the corresponding ciphertext blocks will be different. Additionally, CBC mode uses an Initialization Vector (IV) to provide randomness and prevent patterns in the ciphertext. The IV is XORed with the first plaintext block before encryption. Therefore, CBC mode not only encrypts the message but also provides authentication by ensuring the integrity of the ciphertext.

The given answer consists of the variables p and g. These variables are mentioned in the question as the public parameters for the DH protocol. The variable p represents a prime number, while g represents a generator. These parameters are essential for the DH protocol as they help in generating the shared secret key between two parties.

The correct answer is C = E(D(E(P,K1),K2),K1). This is the correct notation for 3DES sa EDE2. It shows that the plaintext (P) is first encrypted with key K1, then decrypted with key K2, and finally encrypted again with key K1. This triple encryption process provides stronger security compared to single DES encryption.

The question is asking for the additive inverse of the number 3 (mod 7). In modular arithmetic, the additive inverse of a number is the number that, when added to the original number, gives a sum that is congruent to 0 modulo the given modulus. In this case, the modulus is 7. The additive inverse of 3 (mod 7) is 4, because 3 + 4 = 7, which is congruent to 0 modulo 7.

The AES algorithm allows for different key lengths to be used, including 192 bits, 128 bits, and 256 bits. These key lengths determine the level of security provided by the algorithm. A longer key length generally provides stronger security, as there are more possible combinations for the key. Therefore, 192 bits, 128 bits, and 256 bits are all valid key lengths for the AES algorithm.

The correct answer states that symmetric cipher systems are faster and the key of the asymmetric system is longer compared to the key of the symmetric system. This means that symmetric cipher systems are faster in terms of encryption and decryption processes. Additionally, asymmetric systems require longer keys for encryption and decryption compared to symmetric systems, which adds to the complexity and security of the asymmetric system.

Cut and paste is a possible attack on block ciphers in ECB mode. In this attack, the attacker intercepts the ciphertext and rearranges the blocks to create a new ciphertext. By doing so, the attacker can manipulate the plaintext without knowing the encryption key. This attack is possible because ECB mode encrypts each block independently, allowing the attacker to rearrange the blocks without affecting the decryption process. This can lead to serious security vulnerabilities, which is why ECB mode is not recommended for secure encryption.

The given correct answer states that the functions in the AES algorithm are invertible. This means that for every output of the function, there exists a unique input that produces that output. In other words, it is possible to reverse the function and obtain the original input from the output. This property is crucial in encryption algorithms like AES, as it allows for the decryption process to retrieve the original message from the encrypted data.

The correct answer is "Man in the middle" because the DH algorithm is vulnerable to this type of attack. In a man-in-the-middle attack, an attacker intercepts communication between two parties and impersonates each party to the other, allowing them to intercept and manipulate the data being transmitted. This can compromise the security of the DH algorithm, as the attacker can potentially gain access to the shared secret key and decrypt the communication.

PKI (Public Key Infrastructure) predstavlja sisteme koji koriste javne i privatne ključeve. Javni ključ se koristi za šifrovanje podataka, dok se privatni ključ koristi za dešifrovanje podataka. Ova kombinacija ključeva omogućava sigurnu razmenu podataka između korisnika, jer samo osoba sa odgovarajućim privatnim ključem može dešifrovati podatke koji su šifrovani javnim ključem. Ovo omogućava autentifikaciju korisnika i bezbednu komunikaciju na internetu.

The given correct answer states that the encryption process for RSA algorithm is C = M^e mod N. In RSA encryption, the ciphertext (C) is calculated by raising the plaintext (M) to the power of the public exponent (e) and then taking the modulo N. This process ensures that the ciphertext is only decryptable with the corresponding private key.

The correct answer is "Samo strani koja digitalno potpisuje" (Only the party that digitally signs). In the process of digital signing using the RSA algorithm, the private key is only known to the party that is digitally signing the message. This ensures that the digital signature is unique to that party and verifies the authenticity and integrity of the message. The private key should not be known to any other party, including the party receiving the message or the certification authority.

The correct answer is "Tip blokovske sifre" because Fejstel sifra (Feistel cipher) is a type of block cipher. In a Feistel cipher, the plaintext is divided into blocks and each block undergoes a series of transformations using a round function and a key. This type of cipher is commonly used in symmetric encryption algorithms to ensure confidentiality and security of data.

Triple DES with three independent keys uses a key size of 168 bits. This means that each key used in the encryption process is 56 bits long. Triple DES is a symmetric encryption algorithm that applies the Data Encryption Standard (DES) algorithm three times in a row to provide enhanced security. By using three keys, it increases the key size and makes it more difficult for attackers to decrypt the encrypted data.

The correct answer is C = E(D(E(P,K1),K2),K3). This answer correctly represents the notation for triple DES, where P is the plaintext, K1, K2, and K3 are the three keys used for encryption and decryption, E represents the encryption function, and D represents the decryption function. The notation shows that the plaintext P is first encrypted with K1, then decrypted with K2, and finally encrypted again with K3 to produce the ciphertext C.

The number of rounds in the DES algorithm is 16.

The correct answer is "Diskretnog logaritma." The secrecy of the Diffie-Hellman (DH) algorithm is based on the computational complexity of calculating discrete logarithms. In DH, two parties can exchange public keys over an insecure channel and use those keys to establish a shared secret key without directly exchanging the key itself. This is possible because calculating the discrete logarithm in a finite field is computationally difficult, making it hard for an attacker to determine the shared secret key even if they have access to the public keys.

The correct answer is N,e. In the RSA algorithm, the public key consists of two parts: N and e. N represents the modulus, which is the product of two large prime numbers p and q. e represents the public exponent, which is a smaller prime number that is coprime with (p-1) * (q-1). The public key is used for encryption, while the private key (not mentioned in the question) is used for decryption.

The principle of diffusion refers to the characteristic of encryption with a random sequence. In this principle, each bit of the ciphertext is a function of all the bits of the plaintext and all the bits of the key. This principle is historically significant and represents a characteristic of classical cipher systems. Therefore, the correct answer is that each bit of the ciphertext is a function of all the bits of the plaintext and all the bits of the key.

The given answer includes a list of block ciphers, which are encryption algorithms that operate on fixed-size blocks of data. The ciphers mentioned in the answer, IDEA, AES, Blowfish, 3DES, and DES, are all well-known and widely used block ciphers in the field of cryptography. These ciphers provide varying levels of security and have been extensively studied and analyzed for their strength against various attacks. The inclusion of these ciphers in the answer suggests that they are considered reliable and effective for securing data.

In block ciphers, encryption is applied to a message divided into fixed-length blocks, and the resulting ciphertext blocks have the same length as the input message blocks. This means that each block of the plaintext message is encrypted into a corresponding block of the ciphertext, maintaining the same length.

We use the private key in digital signature. The private key is used to generate a unique digital signature for a document or message. This signature can be verified using the corresponding public key, ensuring the authenticity and integrity of the data. The private key is kept secret and known only to the owner, while the public key is shared with others for verification purposes. Therefore, the private key is the correct answer for this question.

When Alice and Bob apply the DH algorithm, they establish a secret value that can be used as a symmetric key. The DH algorithm allows two parties to agree upon a shared secret value without directly transmitting it over an insecure channel. This secret value can then be used as a symmetric key for encryption and decryption purposes, ensuring secure communication between Alice and Bob.

A digital certificate can contain the name and surname of the owner as well as their public key. The name and surname of the owner are important pieces of information that can be used to identify the owner of the certificate. The public key is necessary for encrypting and verifying digital signatures. Therefore, both the name and surname of the owner and the public key are commonly included in a digital certificate.

The correct answer is "Koristi javni kljuc posiljaoca." When a message is digitally signed, the sender uses their private key to create a unique signature for the message. The recipient can then use the sender's public key to verify the integrity of the message by comparing the signature with the message itself. By using the sender's public key, the recipient can ensure that the message has not been tampered with during transmission.

The correct answer is that an error in transmission does not accumulate beyond 2 blocks, and an error of 1 bit in transmission affects two blocks in the OT decoding process. This means that if there is an error in the transmission of data, it will only affect a maximum of 2 blocks and will not propagate further. Additionally, if there is a single bit error in transmission, it will impact the decoding of two blocks in the OT process.

The correct answer is that for calculating the MAC code for message integrity verification using block cipher, the CBC mode of operation is used and the MAC represents the last block of the cipher. This means that the message is divided into blocks and each block is encrypted using the CBC mode, where the ciphertext of each block is dependent on the previous block. The MAC code, which is used to verify the integrity of the message, is then derived from the last block of the ciphertext.

The correct answer is "Potpunu pretragu kljuceva" (Brute-force attack). The DES algorithm is vulnerable to a brute-force attack, where an attacker systematically tries all possible keys until the correct one is found. This is because DES has a relatively small key size of 56 bits, making it computationally feasible to try all possible keys within a reasonable amount of time.

3DES sa EDE2 koristi ključ dužine 112 bita. 3DES (Triple Data Encryption Standard) je kriptografski algoritam koji koristi blokovsku šifru DES tri puta za povećanu sigurnost. EDE2 (Encrypt-Decrypt-Encrypt 2) je način implementacije 3DES algoritma koji koristi dva koraka šifriranja i jedan korak dešifriranja. Ključ dužine 112 bita se sastoji od tri ključa od po 56 bita, što ukupno čini 168 bita. Međutim, samo prvih 112 bita se koristi za šifriranje i dešifriranje podataka.

In a hybrid cipher system, the acceptable parameters are a secret key of length 256 bits, a hash value of length 256 bits, and a private and public key of length 2048 bits. This combination ensures a strong level of security for the encryption and decryption process.

The correct answer is the order in which the blocks are listed: P box, S box, K box, E box. This is the correct order of the regular blocks in the DES algorithm. The P box is responsible for permuting the input bits, the S box is responsible for substituting groups of bits, the K box is responsible for generating the round keys, and the E box is responsible for expanding the input bits.

The length of the key in the DES algorithm is 56 bits. DES (Data Encryption Standard) is a symmetric encryption algorithm that uses a 56-bit key to encrypt and decrypt data. This key length was chosen to strike a balance between security and efficiency. However, due to advances in computing power, a 56-bit key is now considered relatively weak and vulnerable to brute-force attacks. As a result, DES is no longer widely used and has been replaced by more secure encryption algorithms with longer key lengths.

The correct answer is "Poverljivost poruke" (Confidentiality of the message). This means that encrypting the plaintext ensures that the message is kept confidential and cannot be accessed or understood by unauthorized individuals.

Simetricni sifarski sistemi koriste isti tajni kljuc za sifrovanje i desifrovanje. U ovakvim sistemima, isti kljuc se koristi kako bi se podaci sifrovali i desifrovali. Ovo omogucava efikasno sifrovanje i desifrovanje podataka, ali zahteva bezbedan nacin deljenja tajnog kljuca izmedju komunikacionih strana.