Session 1. Classical Cryptography. Basic concepts. Cryptology kryptos =secret + logos =(word, language, meaning, science) Cryptology = Cryptography + Cryptanalysis Opposite and complementary at the same time. Basic concepts. Cryptography
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Session 1
Classical Cryptography
KEY
KEY
encipher
Ciphertext
decipher
Plaintext
Plaintext
A
B
Cryptanalysis
decrypt
Gaius Julius Caesar,
100-44 B.C.
Enciphering:
Deciphering:
Note that the modulus of a negative value is computed by repeatedly adding the base until a positive value is obtained.
Blaise de Vigenère (1523-1596)
Sir Francis Beaufort (1774-1857)
Encipherment and decipherment are the same(involution)
Enciphering:
Deciphering:
M
Q
Rotor machines – principle of operation
Source: http://en.wikipedia.org/wiki/Enigma_machine
Binary DecimalLETTERSNUMBERSBinary DecimalLETTERSNUMBERS--------------------------------------------------------------------------------------------------------- 00000 0 BLANK BLANK10000 16 T 5 00001 1 E 310001 17 Z " 00010 2 LF LF10010 18 L ) 00011 3 A -10011 19 W 2 00100 4 SP SP10100 20 H # 00101 5 S BELL10101 21 Y 6 00110 6 I 810110 22 P 0 00111 7 U 710111 23 Q 1 01000 8 CR CR11000 24 O 9 01001 9 D $11001 25 B ? 01010 10 R 411010 26 G & 01011 11 J ‘11011 27 FIGS FIGS 01100 12 N ,11100 28 M . 01101 13 F !11101 29 X / 01110 14 C :11110 30 V ; 01111 15 K (11111 31 LTRS LTRS
P(X = x | Y = y) = P(X = x)
Source: Cipher Systems – Henry Beker, Fred Piper, Northwood Books, 1982.
Source: Kryptografi – Ben Johnsen, Tapir Akademisk Forlag, Trondheim, 2005.