Introduction to Cryptography –
C839 Course Lecture Notes and
Practice Material
Cryptography - ANSWER-The science of altering communication so that it cannot
be understood without having the key.
cipher - ANSWER-The algorithm(s) needed to encrypt and decrypt a message.
Mono-alphabet substitution - ANSWER-Substitute one character of cipher text for
each character of plain text.
Caesar cipher - ANSWER-Every letter is shifted a fixed number of spaces to the left
or the right in the alphabet.
Ciphertext - ANSWER-The resultant text after being subjected to the algorithm
and key.
Atbash Cipher - ANSWER-Reverses the alphabet ( A becomes Z, B becomes Y ... ) -
Mono-Alphabet Substitution Cipher. Hebrew code.
,Affine Cipher - ANSWER-single substitution cipher. Each letter is mapped to a
numerical value, permuted with a math function and then converted back to a
letter.
Affine cipher formula - ANSWER-ax + b (mod M)
ROT13 - ANSWER-One type of substitution cipher in which the entire alphabet is
rotated 13 characters.
Scytale - ANSWER-Physical cylinder used to encrypt messages. Turning the
cylinder produced different ciphers.
Single substitution weaknesses - ANSWER-Preserve the underlying letter and word
frequency. A low-end PC is more than enough to brute force crack a single sub
cipher.
Multi-Alphabet Substitution - ANSWER-Rotates through various keys.
Cipher disk - ANSWER-a physical device used to encrypt. Invented by Leon Alberti
in 1466. The cipher disk was polyalphabetic; each time you turned the disk, you
used a new cipher.
Vignere cipher - ANSWER-Invented in 1553 by Giovan Battista Bellaso. A method
of encrypting text by applying a series of different mono-alphabet ciphers based
on the letters of a keyword.
,Playfair Cipher - ANSWER-Invented by Charles Wheatstone in mid 1800s. Lord
Playfair pushed use of it. Uses a 5x5 table and a key word. Rest of the alphabet is
placed on table in alphabetic order, skipping letters used in the keyword. You
break up the message into two character chunks and return a single character
value. If the letters appear on the same row of your table, replace them with the
letters to the right. If it is on the same column, replace them with the letters
below.
ADFGX Cipher - ANSWER-First cipher used by the German army during WWI. Uses
a modified Polybus 6 x 6 square. Single columnar transposition, 36 letter alphabet.
Polybus square - ANSWER-A 6 x 6 square, used by the ADFGVX cipher. The letters
ADFGVX are used as coordinates for the square.
Homophonic substitution - ANSWER-attempt to make substitution ciphers more
robust by masking the letter frequencies.
nomenclator - ANSWER-Combines a codebook that had a table of homophonic
substitutions.
Null cipher - ANSWER-Hiding the message in unrelated plaintext, and using a
prearranged pattern to take certain letters from the plaintext to uncover the true
message.
Book cipher - ANSWER-Both parties agree to use a particular book as the basis.
Then send coordinates for words.
, Rail Fence Cipher - ANSWER-Encrypt a message by altering each letter on a
different row. then write down the text reading from left to right. The recipient
writes the text on two rows, then reconstructs the message.
The Enigma Machine - ANSWER-Electro-mechanical cipher machine used to
decode messages. This machine was used mostly by Nazi Germany When the
operator pressed a key the encrypted cipher text for that plaintext was different
every time.
TypeX - ANSWER-British cipher machine used in WWII. Similar to Enigma but with
improvements and more security.
SIGABA - ANSWER-Rotor machine used by the United States through World War II
into the 1950s. Similar to Enigma but with improvements and more security.
Cryptanalysis - ANSWER-The study of techniques for attempting to defeat
cryptographic techniques and, and attempt to derive the key.
Frequency Analysis - ANSWER-Tool for breaking most classical ciphers by
examining the ciphertext looking for frequencies of letter combinations.
Kasiski Method - ANSWER-A method of attacking polyalphabetic substitution
ciphers, such as Vignere. It's used to try to discover patterns and use that
information to decrypt the cipher.
C839 Course Lecture Notes and
Practice Material
Cryptography - ANSWER-The science of altering communication so that it cannot
be understood without having the key.
cipher - ANSWER-The algorithm(s) needed to encrypt and decrypt a message.
Mono-alphabet substitution - ANSWER-Substitute one character of cipher text for
each character of plain text.
Caesar cipher - ANSWER-Every letter is shifted a fixed number of spaces to the left
or the right in the alphabet.
Ciphertext - ANSWER-The resultant text after being subjected to the algorithm
and key.
Atbash Cipher - ANSWER-Reverses the alphabet ( A becomes Z, B becomes Y ... ) -
Mono-Alphabet Substitution Cipher. Hebrew code.
,Affine Cipher - ANSWER-single substitution cipher. Each letter is mapped to a
numerical value, permuted with a math function and then converted back to a
letter.
Affine cipher formula - ANSWER-ax + b (mod M)
ROT13 - ANSWER-One type of substitution cipher in which the entire alphabet is
rotated 13 characters.
Scytale - ANSWER-Physical cylinder used to encrypt messages. Turning the
cylinder produced different ciphers.
Single substitution weaknesses - ANSWER-Preserve the underlying letter and word
frequency. A low-end PC is more than enough to brute force crack a single sub
cipher.
Multi-Alphabet Substitution - ANSWER-Rotates through various keys.
Cipher disk - ANSWER-a physical device used to encrypt. Invented by Leon Alberti
in 1466. The cipher disk was polyalphabetic; each time you turned the disk, you
used a new cipher.
Vignere cipher - ANSWER-Invented in 1553 by Giovan Battista Bellaso. A method
of encrypting text by applying a series of different mono-alphabet ciphers based
on the letters of a keyword.
,Playfair Cipher - ANSWER-Invented by Charles Wheatstone in mid 1800s. Lord
Playfair pushed use of it. Uses a 5x5 table and a key word. Rest of the alphabet is
placed on table in alphabetic order, skipping letters used in the keyword. You
break up the message into two character chunks and return a single character
value. If the letters appear on the same row of your table, replace them with the
letters to the right. If it is on the same column, replace them with the letters
below.
ADFGX Cipher - ANSWER-First cipher used by the German army during WWI. Uses
a modified Polybus 6 x 6 square. Single columnar transposition, 36 letter alphabet.
Polybus square - ANSWER-A 6 x 6 square, used by the ADFGVX cipher. The letters
ADFGVX are used as coordinates for the square.
Homophonic substitution - ANSWER-attempt to make substitution ciphers more
robust by masking the letter frequencies.
nomenclator - ANSWER-Combines a codebook that had a table of homophonic
substitutions.
Null cipher - ANSWER-Hiding the message in unrelated plaintext, and using a
prearranged pattern to take certain letters from the plaintext to uncover the true
message.
Book cipher - ANSWER-Both parties agree to use a particular book as the basis.
Then send coordinates for words.
, Rail Fence Cipher - ANSWER-Encrypt a message by altering each letter on a
different row. then write down the text reading from left to right. The recipient
writes the text on two rows, then reconstructs the message.
The Enigma Machine - ANSWER-Electro-mechanical cipher machine used to
decode messages. This machine was used mostly by Nazi Germany When the
operator pressed a key the encrypted cipher text for that plaintext was different
every time.
TypeX - ANSWER-British cipher machine used in WWII. Similar to Enigma but with
improvements and more security.
SIGABA - ANSWER-Rotor machine used by the United States through World War II
into the 1950s. Similar to Enigma but with improvements and more security.
Cryptanalysis - ANSWER-The study of techniques for attempting to defeat
cryptographic techniques and, and attempt to derive the key.
Frequency Analysis - ANSWER-Tool for breaking most classical ciphers by
examining the ciphertext looking for frequencies of letter combinations.
Kasiski Method - ANSWER-A method of attacking polyalphabetic substitution
ciphers, such as Vignere. It's used to try to discover patterns and use that
information to decrypt the cipher.
