II. Match the word to its explanation

1) cryptography

2) password

3) scheme

4) message

5) mailbox

6) access

7) authorization

8) signature

9) malware

10) solution

a) the approach of entering

b) official permission to have access

c) malicious software

d) a box into which mail is delivered

e) a means of solving a problem or dealing with a difficult situation

f) a string of characters that allows someone access to a computer system

g) a person's name written in a distinctive way as a form of identification

i) a verbal, written, or recorded communication sent to a recipient

j) a systematic plan for a course of action

k) the art of writing or solving codes

III. Match the English and Ukrainian equivalents

1) lock-up a) пароль; ключ доступу

2) proof listing в) перехід з блокуванням

3) mailbox service с) закрита база даних

4) pass key d) розраховане значення

4) authenticity e) передача повідомлень

5) private database f) контрольний роздрукований матеріал

6) mail group g) асиметричне відношення

7) algorithm scheme h) тупик, тупикова ситуація

8) message passing i) служба почтових скриньок

9) locking escape j) достовірність

10) calculated value k) група електронної пошти

11) asymmetric relation l) схема алгоритмів

IV. Read and translate the following text Data security

Public key cryptography, also known as asymmetric cryptography, is a form of cryptography in which a user has a pair of cryptographic keys - a public key and a private key. The private key is kept in secret, while the public key may be widely distributed. A message encrypted with the public key can be decrypted only with the corresponding private key. Secret key cryptography, also known as symmetric cryptography uses a single secret key for both encryption and decryption. The two main branches of public key cryptography are:

- public key encryption — a message encrypted with a recipient's public key can be decrypted by the recipient possessing the corresponding private key. This is used to ensure confidentiality.

- digital signatures — a message signed with a sender's private key can be verified by anyone who has access to the sender's public key. This is used to ensure authenticity.

An analogy for public-key encryption is similar to a locked mailbox with a mail slot. The mail slot is exposed and accessible to the public; its location (the street address) is the public key. Anyone knowing the address can go to the door and drop a message through the slot. However, only the person who possesses the key can open the mailbox and read the message. An analogy for digital signatures is an envelope with a personal wax seal. The message can be opened by anyone, but the seal authenticates the sender. A central problem for public-key cryptography is to prove that a public key is authentic, and has not been tampered with or replaced by a malicious third party. The usual approach to this problem is to use a public-key infrastructure (PKI), known as certificate authorities. Another approach, used by Pretty Good Privacy (PGP), is the "web of trust" method to ensure authenticity of key pairs. Public key techniques are much more computationally intensive than purely symmetric algorithms. In practice, public key cryptography is used with secret-key methods for different reasons. For encryption, the message may be encrypted with secret-key algorithm using a randomly generated key, and that key encrypted with the user's public key. For digital signatures, a message is hashed (using a cryptographic hash function) and the smaller "hash value" is signed; before verifying the signature, the recipient computes the hash of the message and compares this hash value with the signed hash value to check that the message has not been tampered with.

The most obvious application of a public key encryption system is confidentiality; a message which a sender encrypts using the recipient's public key can only be decrypted by the recipient's private key. Public-key digital signature algorithms can be used for sender authentication. For instance, a user can encrypt a message with his own private key and send this key. If another user can successfully decrypt it using the corresponding public key, this provides assurance that the first user sent it. In practice, a cryptographic hash value of the message is calculated, encrypted with the private key and sent with the message. Then the receiver can verify message integrity by calculating the hash value of the received message and comparing it against the decoded signature (the original hash). If the sender and receiver’s hash do not match, the received message is not identical to the message which the sender "signed" or the sender's identity is wrong. To achieve authentication and confidentiality the sender would first encrypt the message using his private key, then the next encryption is performed using the recipient's public key.

An analogy which can be used to understand the advantages of an asymmetric system is to imagine two people, Alice and Bob, sending a secret message through the public mail. In this example, Alice has the secret message and wants to send it to Bob, after which Bob sends a secret reply. With a symmetric key system, Alice first puts the secret message in a box, and then locks the box using a padlock to which she has a key. Then she sends the box to Bob through regular mail. When Bob receives the box, he uses an identical copy of Alice's key (which he has obtained previously, maybe by a face-to-face meeting) to open the box and reads the message. Then Bob can then use the same padlock to send his secret reply. In an asymmetric key system, Bob and Alice have separate padlocks. First, Alice asks Bob to send his open padlock to her through regular mail. When Alice receives the massage she uses the key to lock a box containing her message, and sends the locked box to Bob. Bob can unlock the box with his key and read Alice’s message. To reply, Bob must similarly get Alice's open padlock to lock the box before sending it back to her. The critical advantage of an asymmetric key system is that Bob and Alice never need to send a copy of their keys to each other. This prevents a third party from copying a key while it is in transit.

In a secure asymmetric key encryption scheme, the decryption key should not be deducible from the encryption key. This is known as public-key encryption, since the encryption key can be published without compromising the security of encrypted messages. In the analogy above, Bob might publish instructions on how to make a lock ("public key"), but the lock is such that it is impossible (so far as is known) to deduce from these instructions how to make a key which will open that lock ("private key"). Those wishing to send messages to Bob use the public key to encrypt the message; Bob uses his private key to decrypt it.