Explore topic-wise InterviewSolutions in .

Correct option is (c) a and m are coprime

For explanation: While choosing the VALUES of a and m it should be ensured that a and m are coprime. OTHERWISE DECODING the ciphered TEXT WOULD be difficult.

Correct option is (c) srt

The BEST EXPLANATION: AFFINE cipher uses linear algebra for the purpose of ENCRYPTION It uses the formula a^-1(x-b)%26 for decryption of ciphered text. So the plain text will be “srt”.

Right option is (a) wkxjcgxzra

Easiest EXPLANATION - Affine cipher uses LINEAR ALGEBRA for the PURPOSE of ENCRYPTION. It uses the formula(ax+b)%26 for this purpose. So the ciphered text will be “wkxjcgxzra”.

The CORRECT option is (B) false

Explanation: Affine CIPHER is a very weak cipher as it can be EASILY broken using frequency analysis. It can be easily cracked EVEN if 2 characters are known.

Right choice is (a) Mono ALPHABETIC cipher

The best I can explain: Affine cipher FALLS in the category of mono alphabetic substitution cipher. It uses linear ALGEBRA for encrypting the plain text.

The correct option is (a) a^-1(x-b)%26

To EXPLAIN: Affine cipher uses LINEAR ALGEBRA for the purpose of encryption. It uses the formulaa^-1(x-b)%26 for DECRYPTION of ciphered TEXT.

The correct choice is (b) (ax+b)%26

To explain: AFFINE cipher uses LINEAR algebra for the purpose of ENCRYPTION. It uses the FORMULA (ax+b)%26 for this purpose.

Correct answer is (c) AFFINE cipher

The EXPLANATION is: Affine cipher is the weakest cipher out of the GIVEN options as it is a mono alphabetic cipher and other options are poly alphabetic ciphers. So it is QUITE vulnerable to frequency analysis.

Correct ANSWER is (a) Affine CIPHER

For explanation: Asymmetric cipher makes use of 2 keys for the PURPOSE of encryption. As affine cipher is the only SYMMETRIC cipher out of the given options so it requires only one KEY.

Correct answer is (b) AFFINE CIPHER

The best explanation: Affine cipher is the only cipher out of the GIVEN options that MAKE use of linear algebra for the purpose of encryption. It is a type of mono alphabetic cipher.

The correct choice is (c) it cannot be combined with other ciphers

Easiest explanation - Although columnar TRANSPOSITION cipher is a WEAK cipher in itself. But it can be combined with other substitution ciphers so as to improve its SECURITY. The probability of error remains high while decoding columnar cipher as it is a lengthy PROCESS.

Right option is (b) 2

The explanation is: The NUMBER of columns in the table used for the purpose encryption in columnar transposition cipher will always be equal to the number of letters in the keyword.So when we will write the letters of the plain TEXT row wise then there will be 2 ROWS of plain text in this CASE. The table is shown below :-

S E C R E T

1 S A N F O U

2 N D R Y

The correct answer is (d) LFSECIAISD

Easiest explanation - For encrypting USING columnar cipher we have to arrange the letters of the plain text in a table which has the same NUMBER of columns as the letters of the KEYWORD. Then the letters of the keyword are arranged in alphabetical order and we read along each column.

3 1 4 2 5

G A M E S

C L A S S

I F I E D

So the ciphered text will be “IFSECIAISD”.

The correct answer is (c) 6

The explanation is: The NUMBER of columns in the table used for the PURPOSE encryption in columnar transposition cipher will always be equal to the number of letters in the keyword. So in this case it will be equal to 6.

The correct CHOICE is (B) false

The BEST explanation: Double transposition cipher is formed by applying columnar transposition cipher twice. So it is harder to crack than a simple columnar transposition cipher.

The CORRECT OPTION is (d) additive cipher

To explain: In TRANSPOSITION cipher, the letters remain the same in ciphered and plain text. Their position is only changed whereas in SUBSTITUTION cipher the letters become different in encrypted text. As additive cipher is the only non transposition cipher out of the given OPTIONS so it will be the correct option.

The correct option is (c) Double transposition CIPHER

Explanation: Double transposition cipher is formed by applying columnar transposition cipher twice. For the purpose of encryption, we may USE the same KEY twice or we can use two different KEYS.

Correct answer is (c) DTIPRC

The BEST explanation: We know that TRANSPOSITION CIPHER encrypts the plain text by shuffling the letters of the plain text. So out of the given options, only “DTIPRC” does not have the same set of letters as “CIPHER”.

Right answer is (c) transposition CIPHER

The BEST I can EXPLAIN: COLUMNAR cipher is a transposition cipher. It falls under the CATEGORY of transposition cipher as it encrypts the plain text by rearranging its letters.

The correct choice is (b) PUBLIC KEY cryptography

Explanation: Asymmetric encryption is ALSO known as public key cryptography. Asymmetric CIPHER makes use of 2 keys for the purpose of encryption.

Right ANSWER is (a) Alfred Vail

For EXPLANATION: Alfred Vail ALONG with Samuel Morse developed Morse code. While Jedidiah Morse, Lucretia Pickering Walker were his father and spouse RESPECTIVELY.

Correct option is (b) 2004

The BEST I can explain: On May 24, 2004, the SYMBOL @ was added to the official Morse CHARACTER SET by International TELECOMMUNICATION Union.

Right CHOICE is (d) !

Best explanation: There is no STANDARD representation for the exclamation mark (!) in Morse code. The other symbols have been DEFINED by the International Telecommunication UNION.

The RIGHT choice is (a) Dollar symbol

The explanation is: The symbol 'Dollar symbol' and & are not defined INSIDE the ITU RECOMMENDATION on Morse code. INTERNATIONAL Telecommunication Union is a union that mandated Morse code worldwide.

Correct option is (C) 3 Units

Easiest EXPLANATION - The letters of a word are SEPARATED by a space of 3 UNIT. The representation of dot symbol has 1 unit, while the DASH symbol has 2 units.

The correct OPTION is (a) 1

The explanation is: Since the duration of Space Signal is equal to DOT Duration. So, the space signal is of 1 UNIT. While a dash is 3 units and space between LETTERS is also three units.

Right answer is (b) Aldis

The best EXPLANATION: Prosigns are SPECIAL unwritten PROCEDURAL SIGNALS which are used to show changes in communications protocol STATUS or white space text.

The CORRECT option is (b) CODEX

The EXPLANATION is: CODEX word OFFERS a word RATE that is typical of 5-letter code groups. PARIS is a standard word to measure the operator transmission speed of Morse Code.

Right CHOICE is (d) E

Best explanation: The most COMMON LETTER in English, the letter “E”, has a single dot. Morse code was designed so that the length of each SYMBOL is inverse to FREQUENCY of occurrence in text.

Right OPTION is (d) FRIEDRICH Clemens Gerke

The BEST explanation: It was created by Friedrich Clemens Gerke in 1848 and INITIALLY USED for telegraphy in Germany. Samuel Morse is the inventor of the telegraph after whom Morse code was named.

The correct ANSWER is (a) True

Best explanation: Morse code speed is measured in characters per minute (cpm) as well as in WORDS per minute (wpm). The transmission rate of the Morse code is also measured is GROUPS per UNIT (gpm).

The correct answer is (a) PARIS

Best explanation: PARIS tells about word rate that is TYPICAL of natural language words and reflects the benefits of Morse code’s shorter code DURATIONS for common CHARACTERS such as “E” and “t”.

The correct answer is (b) 1844

Best EXPLANATION: Morse system for telegraphy was first USED in 1844 to MAKE indentations on a PAPER TAPE when electric currents were received.

Right answer is (a) Telegraphy

For EXPLANATION: A CODE was NEEDED to transmit natural language using only the pulses in a TELEGRAPH system. Morse developed the modern INTERNATIONAL Morse code.

The correct option is (a) 3 Dots, 3DASHES, and 3 Dots

For EXPLANATION: In an EMERGENCY the DISTRESS signal is SOS– 3 dots, 3 dashes, and 3 dots – internationally recognized by treaty. It is used to call emergency help when someone is in need.

Correct option is (b) T

Easiest explanation - The common letter in ENGLISH, the letter “T”, has the shortest dash CODE: a single dash. While the letter in English, “E”, has a single dot. It is considered to be the smallest Morse Code EVER DEFINED till now while other LETTERS are larger in time duration.

The CORRECT answer is (a) True

The best I can explain: Morse code was designed so that the length of each SYMBOL is inverse to the frequency of occurrence in TEXT. Therefore, the letter the letter “E”, has a SINGLE dot.

Right answer is (C) 7

For explanation: The WORDS are separated by a SPACE of 7 dot durations. Since the dot duration is of 1 Unit. So, the words are separated by a space of 7 Unit.

The correct option is (c) 3 Dot DURATION

Easiest explanation - The letters of a WORD are separated by a space of 3 dot durations. SINCE the dot duration is of 1 Unit. So, the letters of a word are separated by a space of 3 Unit.

The CORRECT ANSWER is (a) EQUAL to DOT Duration

For explanation: The duration of Space SIGNAL is 1 Unit and Dot Duration is also 1 Unit. So the duration of Space Signal is equal to Dot Duration.

The CORRECT answer is (b) Space

For explanation: Each dot or dash within a character is FOLLOWED by a period of signal absence called Space Signal which is of 1 Unit. The space signal is used after every word in Morse Code.

Correct OPTION is (c) 3

The best I can explain: The duration of a dash is 3 times the duration of a dot as duration of dot is defined to be 1 UNIT in MORSE Code and duration of dash is 3 units in Morse Code.