C839 - Intro Into Cryptology 1-5
Combined WGU with 100%
correct answers
Mono-Alphabet Substitution Cipher - answer Algorithms that simply
substitute one character of cipher text for one character of plain
text, these are the most primitive algorithms
Affine Cipher - answer Any single substitution alphabet ciphers
where each letter in the alphabet is mapped to some numeric value,
permuted with some relatively simple mathematical function, and
then converted back to a letter.
The formula for any basic cipher of this type is ax+b(modM), M
being the size of the alphabet, so for example Caeser cipher would
be 1x+3(mod26)
Scytale Cipher - answer Physical cylinder that was used to encrypt
messages. Turning the cylinder produced different ciphertexts.
Required a cylinder of the same diameter as the cylinder used to
create the message to read the message.
Single substitution weaknesses - answer Literacy rates have risen
since ancient times, all languages have certain word and letter
frequencies, underlying word and letter frequencies lead to
vulnerability to cryptanalysis
Examples of Multi-Alphabet Substitution - answer Cipher Disk,
Vigenere Cipher
Vigenere Cipher - answer Once considered very secure, invented by
Giovan Battista Bellaso in 1553. Used until early 1900's. Encrypts
text by using a series of different Caesar cipher based on a keyword.
,Friedrich Kasiski - answer First person to carry out a successful
attack on a Vigenere cipher
Playfair Cipher - answer Invented by Charles Wheatstone in 1854.
Encrypts two letters instead of one, this makes it more complex.
Uses a 5x5 table containing a keyword. No more secure than any
other older ciphers.
ADFVGX Cipher - answer A transposition cipher invented 1918 by
Fritz Nebel, used a 36 letter alphabet and a modified Polybius
square with a single columnar transposition
Homophonic Substitution - answer Early attempt to make
substitution ciphers more robust, masks letter frequencies, plain
text letters map to multiple cipher text symbols
Null Ciphers - answer Message hidden in unrelated text. Sender and
receiver have pre-arranged to use a pattern to remove certain
letters from the message which leaves only the true message
behind
Book Ciphers - answer Sender and receiver agree on a particular
book, coordinates are then used to locate words of an intended
message in the book
Rail Fence Cipher - answer Most widely known transposition cipher,
encrypts the message by altering each letter on a different row,
message must then be written down left to right and put into rows
Information Theory - answer Modern cryptography began in 1949
when Claude Shannon published a paper about the Mathematical
Theory of Communication. This idea improved cryptography.
,Diffusion - answer Changes to one character in the plain text affect
multiple characters in the cipher text, unlike in historical algorithms
where each plain text character only affect one cipher text
character.
Confusion - answer Occurs by using a complex substitution
algorithm. Attempts to make the relationship between the
statistical frequencies of the cipher text and the key as complex as
possible.
Avalanche - answer A desirable effect where a change to one bit
leads to large change in output. This is Fiestel's take on Claude
Shannon's concept of diffusion. Fiestel's ideas are important when
discussing block ciphers.
How symmetric algorithm encryption is expressed mathematically -
answer C=E(k,p)
Cipher Text (C) is equal to the encryption function (E) with the key
(k) and plain text (p) being passed as parameters to that function.
How symmetric algorithm decryption is expressed mathematically -
answer P=D(k,c)
The plain text (P) is equal to the encryption function (E) with the
key (k) and the cipher text (c) being passed as parameters to that
function.
Substitution - answer Changing some part of the plain text for some
matching part of cipher text. Historical algorithms typically use this.
Two things all modern block cipher algorithms use - answer
Substitution and Transposition
, Binary AND - answer Asks if there is a one in both the first and
second number. Numbers are compared one digit at a time.
Example:
Number A 1101
Number B 0110
returns a result of
Number C 0100
Binary OR - answer Asks if there is a one in the first number, or the
second, or in both numbers. Each place is compared one at a time.
Example:
Number A 1101
Number B 1001
returns a result of
Number C 1101
Binary XOR (exclusive OR) - answer Important because it reversible.
Asks if there is a 1 in one of the numbers but not both. Each place is
compared one at a time. To reverse XOR your result back with your
second number and you will get the first number.
Example:
Number A 1101
Number B 0110
returns a result of
Number C 1011
Combined WGU with 100%
correct answers
Mono-Alphabet Substitution Cipher - answer Algorithms that simply
substitute one character of cipher text for one character of plain
text, these are the most primitive algorithms
Affine Cipher - answer Any single substitution alphabet ciphers
where each letter in the alphabet is mapped to some numeric value,
permuted with some relatively simple mathematical function, and
then converted back to a letter.
The formula for any basic cipher of this type is ax+b(modM), M
being the size of the alphabet, so for example Caeser cipher would
be 1x+3(mod26)
Scytale Cipher - answer Physical cylinder that was used to encrypt
messages. Turning the cylinder produced different ciphertexts.
Required a cylinder of the same diameter as the cylinder used to
create the message to read the message.
Single substitution weaknesses - answer Literacy rates have risen
since ancient times, all languages have certain word and letter
frequencies, underlying word and letter frequencies lead to
vulnerability to cryptanalysis
Examples of Multi-Alphabet Substitution - answer Cipher Disk,
Vigenere Cipher
Vigenere Cipher - answer Once considered very secure, invented by
Giovan Battista Bellaso in 1553. Used until early 1900's. Encrypts
text by using a series of different Caesar cipher based on a keyword.
,Friedrich Kasiski - answer First person to carry out a successful
attack on a Vigenere cipher
Playfair Cipher - answer Invented by Charles Wheatstone in 1854.
Encrypts two letters instead of one, this makes it more complex.
Uses a 5x5 table containing a keyword. No more secure than any
other older ciphers.
ADFVGX Cipher - answer A transposition cipher invented 1918 by
Fritz Nebel, used a 36 letter alphabet and a modified Polybius
square with a single columnar transposition
Homophonic Substitution - answer Early attempt to make
substitution ciphers more robust, masks letter frequencies, plain
text letters map to multiple cipher text symbols
Null Ciphers - answer Message hidden in unrelated text. Sender and
receiver have pre-arranged to use a pattern to remove certain
letters from the message which leaves only the true message
behind
Book Ciphers - answer Sender and receiver agree on a particular
book, coordinates are then used to locate words of an intended
message in the book
Rail Fence Cipher - answer Most widely known transposition cipher,
encrypts the message by altering each letter on a different row,
message must then be written down left to right and put into rows
Information Theory - answer Modern cryptography began in 1949
when Claude Shannon published a paper about the Mathematical
Theory of Communication. This idea improved cryptography.
,Diffusion - answer Changes to one character in the plain text affect
multiple characters in the cipher text, unlike in historical algorithms
where each plain text character only affect one cipher text
character.
Confusion - answer Occurs by using a complex substitution
algorithm. Attempts to make the relationship between the
statistical frequencies of the cipher text and the key as complex as
possible.
Avalanche - answer A desirable effect where a change to one bit
leads to large change in output. This is Fiestel's take on Claude
Shannon's concept of diffusion. Fiestel's ideas are important when
discussing block ciphers.
How symmetric algorithm encryption is expressed mathematically -
answer C=E(k,p)
Cipher Text (C) is equal to the encryption function (E) with the key
(k) and plain text (p) being passed as parameters to that function.
How symmetric algorithm decryption is expressed mathematically -
answer P=D(k,c)
The plain text (P) is equal to the encryption function (E) with the
key (k) and the cipher text (c) being passed as parameters to that
function.
Substitution - answer Changing some part of the plain text for some
matching part of cipher text. Historical algorithms typically use this.
Two things all modern block cipher algorithms use - answer
Substitution and Transposition
, Binary AND - answer Asks if there is a one in both the first and
second number. Numbers are compared one digit at a time.
Example:
Number A 1101
Number B 0110
returns a result of
Number C 0100
Binary OR - answer Asks if there is a one in the first number, or the
second, or in both numbers. Each place is compared one at a time.
Example:
Number A 1101
Number B 1001
returns a result of
Number C 1101
Binary XOR (exclusive OR) - answer Important because it reversible.
Asks if there is a 1 in one of the numbers but not both. Each place is
compared one at a time. To reverse XOR your result back with your
second number and you will get the first number.
Example:
Number A 1101
Number B 0110
returns a result of
Number C 1011
