Encryption for Programmers

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Encryption for
Programmers
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Points of Discussion

• Intro to Crypto
• Code vs Cipher
• Concepts / Examples
• Legalities

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Intro To Crypto

• What is it?
• Language and math techniques for securing
  information
• So, what is encryption?
• Conversion from plaintext to ciphertext
• Historically used for military purposes
• Now, digital signatures, voting, cash, etc
• Everywhere

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Intro To Crypto

• Code
• Substitution
• Whole words, phrases
• Cipher
• Algorithm
• Normally controlled by key

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Intro To Crypto

• Symmetric Key Algorithms
• Private key
• ie, DES and AES
• Asymmetric Key Algorithms
• Public key
• ie, RSA

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Symmetric Key Encryption

• AKA private key
• Same key for encryption and decryption
• Blocks and streams
• Examples DES, AES, and RC4

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Blocks and Streams

• Block cipher, fixed length of bits
• Transformation controlled by secret key

• Stream cipher, each bit or byte

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Asymmetric Key Encryption

• AKA public key
• No transfer of secret key
• 2 keys used
• Public encryption
• Private decryption
• Digital signing
• DSA and ElGamal

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Algorithms

• Alberti, Vigenère, ROT13
• DES / AES
• BLOWFISH
• RSA
• RC5
• RC6
• One Time Pads

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Alberti, Vigenère, ROT13

• Polyalphabetic substitution

ABCDEFGHIJKLMNOPQRSTUVWXYZ BCDEFGHIJKLMNOPQRSTUVWX
YZA CDEFGHIJKLMNOPQRSTUVWXYZAB DEFGHIJKLMNOPQRSTUV
WXYZABC EFGHIJKLMNOPQRSTUVWXYZABCD
FGHIJKLMNOPQRSTUVWXYZABCDE GHIJKLMNOPQRSTUVWXYZABC
DEF HIJKLMNOPQRSTUVWXYZABCDEFG IJKLMNOPQRSTUVWXYZA
BCDEFGH JKLMNOPQRSTUVWXYZABCDEFGHI
KLMNOPQRSTUVWXYZABCDEFGHIJ LMNOPQRSTUVWXYZABCDEFGH
IJK MNOPQRSTUVWXYZABCDEFGHIJKL NOPQRSTUVWXYZABCDEF
GHIJKLM...ZABCDEFGHIJKLMNOPQRSTUVWXY
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Alberti, Vigenère, ROT13

• 1466 Renaissance scholar
• 1586 French Diplomat, crypto
• Good example bad encyption

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Alberti, Vigenère, ROT13
perl -pe tr/A-Za-z/N-ZA-Mn-za-m/ lt input_file gt
output_file
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DES

• DES is insecure
• First published in 1975 (77 standard)
• 64 bit block size, 56 bit key size
• Feistel structure with 16 rounds

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Feistel

• Operations are very similar
• Requires only a reversal of key schedule
• Repeated operations
• Bit shuffling (P-boxes)
• Non-linear functions (S-boxes)
• Linear mixing using XOR

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DES

• Expansion half block is expanded
• Key mixing result is combined with subkey. 16
  subkeys from key schedule.
• Substitution block is then divided into 8
  pieces, s-boxes go to work.
• Permutation outputs are then rearranged to a
  fixed p-box

S1
Half Block
32bit
P-box
.......
Subkey
S8
48bit
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AES

• aka Rijndael
• US Government standard
• First published in 1998 (2001 standard)
• 128 bit block, 128, 192, or 256 bit key size
• Substitution permutation structure
• 10, 12, and 14 rounds

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AES

• 4x4 array, state
• SubBytes substitution with lookup table
• ShiftRows transposition
• MixColumns mix and combine
• AddRoundKey each byte with key using key
  schedule
• Final round does not MixColumns

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AES
Lookup Table
SubBytes
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AES
ShiftRows
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AES
MixColumns
c(x)
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AES
AddRoundKey
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AES

• Implementation

http//fp.gladman.plus.com/cryptography_technology
/rijndael/
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RSA

• Asymmetric
• First for signing and encryption
• 1973 Clifford Cocks, GCHQ
• 1977 by R. Rivest, A. Shamir, L. Adleman

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RSA
p 61 (first prime, kept secret or delete) q
53 (second prime, kept secret or delete) n pq
3233 (modulus, public) e 17 (public exponent,
public) d 2753 (private exponent, private)
Public key is (e, n), private key is d. To
encrypt, where m is plaintext encrypt(m) me
mod n m17 mod 3233 To decrypt, where c is
ciphertext decrypt(c) cd mod n c2753 mod
3233 To encrypt plaintext value 123
encrypt(123) 12317 mod 3233 855 To decrypt
ciphertext 855 decrypt(855) 8552753 mod 3233
123
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RSA

• Padding schemes
• m0 or m1 always 0 or 1
• Low exponents may be less than mod. Thus
  decryption through eth root of ciphertext
• Digital Signing
• Hash d mod n x
• x e mod n hash?

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BLOWFISH

• 1993 by Bruce Schneier
• Block size of 64bit, key size from 32-448 bits
• Feistel structure with 16 rounds
• Implementation
• http//www.schneier.com/blowfish.html

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BLOWFISH
8 bits
8 bits
8 bits
8 bits
32 bits
32 bits
32 bits
32 bits
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RC5

• Block cipher
• First published 1994, R. Rivest
• Block size of 32, 64, or 128bit. Key size up to
  2040 bits.
• Feistel structure, 12 rounds

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RC6

• Block cipher
• R.Rivest,M.Robshaw, R.Sidney, Y.Lisa Yin
• Block size of 128, key sizes of 128, 192, 256 bit.

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One Time Pads

• Vernam Cipher, Unbreakable
• Plaintext combined with pad
• Pad has at least same length
• Drawbacks
• Random Pads
• Secure exchange of pad
• ONE TIME USE
• Integrity

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One Time Pads
A0B1Z25
QIADJ
HELLO
H (7) E (4) L (11) L (11) O (14)
JEPSW

J (9) E (4) P (15) S (18) W (21)
Q (16) I (8) A (26) D (29) J (35)
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One Time Pad
A0B1Z25
HELLO
QIADJ
Q (16) I (8) A (26) D (29) J (35)
JEPSW
-
J (9) E (4) P (15) S (18) W (21)
H (7) E(4) L (11) L (11) O (14)
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Legal

• US Import laws none
• Export Wassenaar Agreement
• Software is not included as a restricted
  technology if it is "generally available to the
  public" or "in the public domain".

• http//rechten.uvt.nl/koops/cryptolaw/
• http//www.wassenaar.org

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Questions?
Contact me riscphree_at_gmail.com http//riscit.info