D830 Study Guide Question with Verified
Correct Answers
Cryptology
The art and science of making and breaking "secret codes
Cryptography
The making of "secret codes."
Cryptanalysis
The breaking of "secret codes."
Crypto
A synonym for any or all of the above (and more), where the precise meaning should be clear
from context.
cipher or cryptosystem
used to encrypt data.
plaintext
normal text that has not been encrypted
Cryptosystem
it is an implementation of cryptographic techniques to provide information security services
(such as confidentiality and integrity).
Ancient Egypt
The earliest known encrypted text found in Egypt dates back to (nearly) 1900 BC.
Hieroglyphics on pharaohs and dignitaries tombs had been hiding secrets, and were disclosed
,(nearly) four millennia later. Secrets were represented as symbols (i.e. hieroglyphics),
unreadable to those who did not (and still do not) know the hieroglyphics alphabet.
Greece.
In 500s BC, Greeks developed cylinder messages. The cipher made use of a baton (called
scytale). Each baton round had the capacity to write letters. represents the secret key. First, a
parchment was wound up in spiral around the baton. Second, the text to be encrypted was
written on the parchment in straight lines (in rows). Third, the parchment was unrolled; and it
represented the ciphertext. The recipient of the ciphertext was required to possess a baton
(with the same diameter than that of the sender) on which the received parchment was wound
up to recover the plaintext. Figure 2.3.2 illustrates an example of a message encryption using
the Greek scytale. The plaintext is TWO THOUSAND SOLDIERS ONSITE ON
SATURDAY; spaces are removed before writing the plaintext on a parchment wound up
around a baton with a diameter of six letters. When the parchment is unrolled, the yielded
ciphertext is TUOSEUWSLOOROADNNDTNISSAHDEIAYOSRTT.
Rome
With no doubt, the most known cipher was developed in Rome 2000 years ago, and referred
to as Caesar's cipher. The code was mainly used to secure communications between
commanders and troops on battlefields or between Rome and provincial governors. Caesar's
cipher is a substitution cipher, where a letter is shifted by some fixed position number; i.e.
letter at position in alphabet is replaced by letter at position . This number, , was the secret
key of the cipher. Caesar's cipher is presented in more detail in Section 5.8.
Vigenere's cipher
In the 1500s, Blaise de Vigenere made improvements to Caesar's cipher. A 26-by-26 table is
used to substitute letters, so that the same letter is not always replaced by the same letter as
, Caesar's cipher does. This is the base concept of polyalphabetic ciphers, which are harder to
break than Caesar's cipher. Vigenere's cipher is presented in more detail in another chapter.
Jefferson's wheel cipher.
In the late 1700s, Thomas Jefferson came up with a cipher system similar to that of Vigenere,
but with higher security, because it has much more combinations to select keys. As illustrated
by Figure 2.3.3, Jefferson's cylinder is composed of 36 disks (or wells), stacked on top of
each other around an axle. The 26 Latin letters are randomly inscribed on each disk. The
disks are numbered; they are removable and can be mounted on the axle in any desired order.
The order of disk mounting represents the secret key. Both the sender and receiver of a
message had to mount the disks in the same way.
Enigma machine.
The Enigma machine, invented during World War I and improved during World War II, was
mainly used by the army of the third Reich. Enigma is one of the first electromechanical
devices used for encryption and decryption; and the most used in practice at that time. It is a
very sophisticated version of Jefferson's cylinder. Enigma was very hard to break; but Alan
Turing did it. Enigma machine is presented in more detail in another chapter.
Vernam's cipher.
In 1917, the one-time pad (OTP) cipher was (re)invented by Gilbert Vernam and patented in
the US. OTP cannot be cracked, because a single-use random key is required for each
message, and the key must be at least of the same bit-length than that of the message to
encrypt. Vernam's cipher was a cipher that combined a message with a key read from a paper
tape or pad; hence, the word pad in the name of the cipher. OTP was used in limited number
of applications, including military applications, because a new key is required for each
message. OTP is discussed in more detail in another chapter.
Correct Answers
Cryptology
The art and science of making and breaking "secret codes
Cryptography
The making of "secret codes."
Cryptanalysis
The breaking of "secret codes."
Crypto
A synonym for any or all of the above (and more), where the precise meaning should be clear
from context.
cipher or cryptosystem
used to encrypt data.
plaintext
normal text that has not been encrypted
Cryptosystem
it is an implementation of cryptographic techniques to provide information security services
(such as confidentiality and integrity).
Ancient Egypt
The earliest known encrypted text found in Egypt dates back to (nearly) 1900 BC.
Hieroglyphics on pharaohs and dignitaries tombs had been hiding secrets, and were disclosed
,(nearly) four millennia later. Secrets were represented as symbols (i.e. hieroglyphics),
unreadable to those who did not (and still do not) know the hieroglyphics alphabet.
Greece.
In 500s BC, Greeks developed cylinder messages. The cipher made use of a baton (called
scytale). Each baton round had the capacity to write letters. represents the secret key. First, a
parchment was wound up in spiral around the baton. Second, the text to be encrypted was
written on the parchment in straight lines (in rows). Third, the parchment was unrolled; and it
represented the ciphertext. The recipient of the ciphertext was required to possess a baton
(with the same diameter than that of the sender) on which the received parchment was wound
up to recover the plaintext. Figure 2.3.2 illustrates an example of a message encryption using
the Greek scytale. The plaintext is TWO THOUSAND SOLDIERS ONSITE ON
SATURDAY; spaces are removed before writing the plaintext on a parchment wound up
around a baton with a diameter of six letters. When the parchment is unrolled, the yielded
ciphertext is TUOSEUWSLOOROADNNDTNISSAHDEIAYOSRTT.
Rome
With no doubt, the most known cipher was developed in Rome 2000 years ago, and referred
to as Caesar's cipher. The code was mainly used to secure communications between
commanders and troops on battlefields or between Rome and provincial governors. Caesar's
cipher is a substitution cipher, where a letter is shifted by some fixed position number; i.e.
letter at position in alphabet is replaced by letter at position . This number, , was the secret
key of the cipher. Caesar's cipher is presented in more detail in Section 5.8.
Vigenere's cipher
In the 1500s, Blaise de Vigenere made improvements to Caesar's cipher. A 26-by-26 table is
used to substitute letters, so that the same letter is not always replaced by the same letter as
, Caesar's cipher does. This is the base concept of polyalphabetic ciphers, which are harder to
break than Caesar's cipher. Vigenere's cipher is presented in more detail in another chapter.
Jefferson's wheel cipher.
In the late 1700s, Thomas Jefferson came up with a cipher system similar to that of Vigenere,
but with higher security, because it has much more combinations to select keys. As illustrated
by Figure 2.3.3, Jefferson's cylinder is composed of 36 disks (or wells), stacked on top of
each other around an axle. The 26 Latin letters are randomly inscribed on each disk. The
disks are numbered; they are removable and can be mounted on the axle in any desired order.
The order of disk mounting represents the secret key. Both the sender and receiver of a
message had to mount the disks in the same way.
Enigma machine.
The Enigma machine, invented during World War I and improved during World War II, was
mainly used by the army of the third Reich. Enigma is one of the first electromechanical
devices used for encryption and decryption; and the most used in practice at that time. It is a
very sophisticated version of Jefferson's cylinder. Enigma was very hard to break; but Alan
Turing did it. Enigma machine is presented in more detail in another chapter.
Vernam's cipher.
In 1917, the one-time pad (OTP) cipher was (re)invented by Gilbert Vernam and patented in
the US. OTP cannot be cracked, because a single-use random key is required for each
message, and the key must be at least of the same bit-length than that of the message to
encrypt. Vernam's cipher was a cipher that combined a message with a key read from a paper
tape or pad; hence, the word pad in the name of the cipher. OTP was used in limited number
of applications, including military applications, because a new key is required for each
message. OTP is discussed in more detail in another chapter.
