A Brief History of
Cryptography
______________
Florian Deckert
23.03.2007

Encyclopedia Britannica:
“Cryptography: Practice of the enciphering and
deciphering of messages in secret code in order
to render them unintelligible to all but the intended
receiver.”
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Early Cryptography
• 3500 BC: Sumerians
– Cuneiform writings
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Early Cryptography
• 1900 BC: Egypt
– First known use of cryptography
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Early Cryptography
• 500 – 600 BC:
ATBASH Cipher
– Used by Hebrew
scribes
– Substitution cipher
(reversed alphabet)
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Early Cryptography
• 486 BC: Greece
– σκυτάλη – skytale
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Early Cryptography
• 60 – 50 BC: Julius Caesar
– substitution cipher
– Shift letters by X positions:
• E.g. X = 3: A D, B E,
C F, ...
– Weakness?
• Frequency analysis (1000 AD)
– 1466: Leon Albertini: cipher
disk
• Used until 16th century
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Medieval Cryptography
• 1587: Vigenère Cipher
– Polyalphabetic: one to
many relationship
– Example
• Encrypt: lamp
• Keyword: ubc
• Ciphertext: fboj
• Apart from that...
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Modern Cryptography
• 1845: Morse Code
– Represention by code
signal
– States (on and off)
composed into 5
symbols
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Modern Cryptography
• 1863: Kasiski breaks Vigenere:
– Find length of keyword
– Divide message into substitution cryptograms
– Use frequency analysis to solve these
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Modern Cryptography
• 1918: ADFGVX Cipher
– Used in the German army in WWI
A D F G X
B T A L P
A
D H O Z K
D
Q F V S N
F
G J C U X
G
M R E W Y
X
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Modern Cryptography
• 1918: The Enigma
– Arthur Scherbius
– Business: confidential
docs
– No codebooks
– Rotors multi
substitution
– Wireing changes as-you-
type
– German forces in WWII
– Room 40
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Modern Cryptography
• 1937 – 1945: Navajo Code Talkers
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Modern Cryptography
• 1949: Shannon:
– Communication
Theory of Secret
Systems
– Proved: One time pad
unbreakable
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Modern Cryptography
• Until mid 70‘s
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Modern Cryptography
• 1976: Diffie – Hellman Key Exchange
– Whitfield Diffie and Martin Hellman
– Discrete logarithm problem:
• G: finite cyclic group with n elements
• Modulo n multiplication
• b: generator of G: every element g of G can be
written as g = bk for some integer k
• Goal: find k given g and b and n!
• Very hard problem
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Modern Cryptography
• So how does it work?
• Exploits?
– Man in the middle
– Fix: additional authentication
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Modern Cryptography
• Public Key Crypto
– Key exchange problem
– Asymmetric key algorithm
– E.g: RSA, MIT, 1977
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Modern Cryptography
• 1991: PGP Pretty Good Privacy
– Protocol, uses RSA
– Encryption & decryption
– Digital signatures
• How does that work?
– Web of Trust
• Third party signs (public) key to attest association
between person and key
– Other Possibility: Hierarchical, CA based
• E.g.: X.509 Certificates in SSL
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Thank You!
Let’s go to Koerner’s.