Post on 14-Dec-2015
Jeff Ehme
Spelman College
jehme@spelman.edu
Chris Christensen
Northern Kentucky University
christensen@nku.edu
Public- and Private-Key Cryptography
DROSX DOBOC DSXQW KDROW KDSMK VKCZO MDCYP ZELVS FUOIM SZROB CRKFO CZKBU ONSXD OBOCD LIWKD ROWKD SMCPK MEVDI SXDRO COMSZ ROBCK CKZZV SMKDS YXCYP WKDRO WKDSM CDRKD MKXLO ZBOCO XDONS XEXNO BQBKN EKDOM YEBCO CYPDO XSQXY BONRY GOFOB KBODR OWYNO BXZBS FKDOU OIMSZ ROBCD ROGYB URYBC OCYPM BIZDY QBKZR IWYNO BXZBS FKDOS OIMSZ ROBCK BOOAE KVVIW KDROW KDSMK VVISX DOBOC
DSXQ
Simple Substitution Cipher
If the solution to a problem can be quickly verified by a computer, can the computer also
solve that problem quickly?
P vs NP
Data Encryption Standard 1977Horst Feistel (1915 – 1990)
Simplified DES: Wade Trapp and Lawrence Washington
DES
64-bit block56-bit key (8 parity bits)8 S-boxes 6 x 416 roundsFeistel cipher
12-bit block9-bit key2 S-boxes 4 x 34 roundsFeistel cipher
DES
Simplified DES
9 bits of key 111 010 110
Use the 8 bits on the left for k1 1110 1011 Rotate to the left one bit 110 101 101Use the 8 bits on the left for k12 1101 0110 Rotate to the left 1 bit 101 011 011Use the 8 bits on the left for k3 1010 1101 Rotate to the left 1 bit 010 110 111Use the 8 bits on the left for k4 0101 1011
Key Schedule
S-Box1 0 1 2 3 4 5 6 7
0 101 010 001 110 011 100 111 000
1 001 100 110 010 000 111 101 011
S 2 0 1 2 3 4 5 6 7
0 100 000 110 101 111 001 011 010
1 101 011 000 111 110 010 001 100
S
DES Decryption
1 1
1 1
,
,
i i i ii i
i i i ii i
L R R L f R K
L R f R K R L
1 1,
i i
i i i ii i
L R
L R R L f R K Encryption
Decryption
Perfect SecurityRandom key, as long as the message, and used only
once.
Computational Security
Today112
Security Level
Symmetric Key RSA and DH ECC80 1024 160
112 2048 224128 3072 256192 7680 384256 15360 521
Skipjack/Clipper ChipSkipjack declassified 1998
Clipper Chip 1993 -1996
64-bit block80-bit key32 roundsUnbalanced Feistel cipher
Diffusion: “… the statistical structure of [the message] which leads to its redundancy is dissipated into long range statistics.”
Wire crossing, S-box
Confusion: “… make the relation between the simple statistics of [the ciphertext] and the simple description of [the key] a very complex and involved one.”
Permutation, P-box
“The Theory of Secrecy Systems 1949
Advanced Encryption Standard 2001Joan Daemen and Vincent Rijmen
Simplified AES: Mohammad Musa, Edward Schaefer, and
Stephen Wedig
AES
128-bit block128-bit, 192-bit, or 256-bit key10, 12, or 14 roundsSPN
16-bit block16-bit key
2 roundsSPN
AES (Rijandael)
Simplified AES
Simplified IDEAHoffman, N. 2007.“A Simplified IDEA Algorithm,”Cryptologia 31(2), 143 – 151.
TEAHolden, J. 2013.“Demitasse: A ‘Small’ Version of the Tiny Encryption Algorithm and Its Use in a
classroom Setting.”Cryptologia 37(1), 74 – 83.
Simplified Symmetric Key Block Ciphers
Simplified DESTrappe, W. and Washington, L.Introduction to Cryptography with Coding Theory
Simplified IDEAHoffman, N. 2007.“A Simplified IDEA Algorithm,”Cryptologia 31(2), 143 – 151.
References
PRESENTBoganov, A. and others. 2007.“PRESENT: An Ultra-Lightweight Block
Cipher.”(Search the net.)
Simplified AESMusa, A., Schaefer, E., and Wedig, S.
2010.“A Simplified AES Algorithm and Its
Linear and Differential Cryptanalysis,”Cryptologia 27(12), 148 – 177.
References