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history of cryptography

Nov 24, 2014

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Steganography and History of CryptographyDr. Ron Rymon Efi Arazi School of Computer Science IDC, Herzliya. 2010/11Pre-Requisites: None1

Overviewj Steganography j History of Cryptography j Modern Cryptography j General Model of Modern Cryptography

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Steganography

Main source: The Code Book / Singh3

Steganographyj In Greek Steganos = covered Graphein = to write

j Steganography is about hiding messages j Historically, secret messages were often hidden (or

memorized)j Today, steganography is used primarily to protect digital

rights watermarking copyright notices fingerprinting a serial ID4

History of Steganography (Physically Hiding)j Runners were memorizing messages Sometimes killed after delivering the message

j Demaratus tells Athens of Persias attack plans Writes the secret message on a tablet, and covers it with wax

j Greek Histaiaeus encouraged Aristagoras of Miletus to

revolt against the Persian King.

Writes message on the shaved head of the messenger, and sends him after his hair grew

j Chinese silk balls Message is written on silk, turned into wax-covered ball that was swallowed by the messenger

j Invisible ink-jet technology Ink that is too small for human eye (Univ of Buffalo, 2000)5

History of Steganography (cont.)j Invisible Ink Certain organic fluids (milk, fruit juice) are transparent when dried but the deposit can be charred and is then visible Romans used to write between the lines A mixture of alum and vinegar may be used to write on hardboiled eggs, so that can only be read once shell is broken

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History of Steganography (cont.)j Microdots WW2 Germany - documents shrunk to the size of a dot, and embedded within innocent letters DNA microdot, embedding synthetically formed DNA sequence (secret) into a normal DNA strand, then posting as microdot Inkjet dots, smaller than human eye can see Microdots with barcode-like information j Easter eggs Programmers embed in software See http://www.eeggs.com

Claims that Beatles embedded secret messages in their music

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Hiding a message within a textj An actual message from a German spy read second letter in each word

Apparently, neutrals protest is thoroughly discounted and ignored. Isman hard hit. Blockade issue affect pretext for embargo on by products, ejecting suets and vegetable oils. Pershing Sails from NY June 18

Hiding a message within a text (more)j Shift some words by one point/pixel. Shifted words (or their first letters) make the sentence j Use different fonts Letter by letter or word by word (Francis Bacon Cipher) j Lexical steganography uses the redundancy of the

English language I feel well and I feel fine seem the same, but one may be used to encode SOS

j Chaffing and winnowing Riddle text with extra parts that the receiver will know how to remove (e.g., those that dont authenticate)9

Modern Steganographyj Hiding one message within another (container) j Most containers are rich media Images, audio, video are very redundant, can be tweaked without affecting human eye/ear US argued that Bin Laden implanted instructions within taped interviews j Copyright notices embedded in digital art Prove ownership Serial number embedded to prevent replication Seek infringements on the web using spiders j Digital cameras EXIF tags Not secretive, but hidden from the eye Embed info such as camera type, date, shutter speed, focal length,.. j Similarly, possible to embed messages in invisible parts of html pages

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Hiding a Message in an Imagej Example: use 1-2 Least Significant Bits (LSB) in each pixel human eye wont notice the difference message can be compressed to reduce number of bits needed only half the bits are likely to change on average prefer containers with a lot of variations j Message (M1) in an Image Steganography is the art and science of communicating in a way which hides the existence of the communication. In contrast to cryptography, where the "enemy" is allowed to detect, intercept and modify messages without being able to violate certain security premises guaranteed by a cryptosystem, the goal of steganography is to hide messages inside other "harmless" messages in a way that does not allow any "enemy" to even detect that there is a second secret message present [Markus Kuhn 1995-07-03].

j Check out Steganos (www.steganos.com), Digimarc

(www.digimarc.com)

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Example (Steganos)Original Picture Embedded Picture

With embedded picture

JPG version

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Steganalysisj Detection: is there a hidden message? Develop signatures for known steganographic tools, e.g. in LSB method, expect local homogeneity When content is encrypted, the message should have a high entropy (white noise) Promising results: high detection rates j Decoding: recover hidden message No significant work in this area ! j Prevention: destroy or remove a hidden message Most steganographies not robust to image alterations Short messages (e.g. copyright) can be encoded redundantly and survive an alternation

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Steganography (Summary)j Steganography is arguably weaker than

cryptography because the information is revealed once the message is intercepted not hidden may attract attention, and in some cases may itself incriminate the messenger conjunction with cryptography

j On the other hand, an encrypted message that is

j In any event, steganography can be used in

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History of Cryptography

Main source: The Code Book / Singh15

Cryptographyj In Cryptography, the meaning of the message is

hidden, not its existence Kryptos = hidden in Greek

j Historically, and also today, encryption involves transposition of letters Spartas scytale is first cryptographic device (5th Century BC) Message written on a leather strip, which is then unwound to scramble the message

substitution Hebrew ATBASH ( ) Kama-Sutra suggests that women learn to encrypt their love messages by substituting pre-paired letters (4th Century AD) Cipher replace letters Code replace words

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Monoalphabetic Ciphersj Caesar Shift Cipher Each letter substituted by shifting n=3 places EXAMPLE HADP SOH

Only 25 such ciphers

j Jefferson wheel implementation Set the message across the wheels Select another line (in random) as cipher

j Substitution based on key phrase Substitution key consists of phrases letters (uniquely) followed by rest of the alphabet in order Phrase: THIS IS ALICE AND BOBS KEY Key: THISALCENDBOKY-FGJMPQRUVWXZ

26! (roughly 1026) monoalphabetic substitution ciphers17

Breaking Monoalphabetic Ciphersj The Arabs broke monoalphabetic substitution using

frequency analysis In English (Source: Beker & Piper)a b c d e f g h i 8.2% 1.5 2.8 4.3 12.7 2.2 2.0 6.1 7.0 j k l m n o p q r 0.2 0.8 4.0 2.4 6.7 7.5 1.9 0.1 6.0 s t u v w x y z 6.3 9.1 2.8 1.0 2.4 0.2 2.0 0.1

Thus, letters ciphering e, t, and a are easily discovered Subsequently can look for the rest of the letters and letter pairs

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Homophonic Substitutionj Homophonic substitution cipher can be used to

foil frequency analysis Keyed 2-digit substitutionA B C D E F G H I T H E K 06 43 71 90 07 44 72 91 08 45 73 92 09 46 74 93 10 47 50 94 11 48 51 95 12 49 52 96 13 25 53 97 14 26 54 98 J 15 27 55 99 K L M N O P Q R S T U V W X Y/Z 16 28 56 75 17 29 57 76 18 30 58 77 19 31 59 78 20 32 60 79 21 33 61 80 22 34 62 81 23 35 63 82 24 36 64 83 00 37 65 84 01 38 66 85 02 39 67 86 03 40 68 87 04 41 69 88 05 42 70 89

Reverse frequencyA B C D E F G H I J K L M N O P Q R S T U V W X Y Z 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 00 01 02 03 04 68 05 43 44 45 46 47 48 49 25 26 29 30 31 32 33 35 36 37 38 40 87 71 73 74 50 53 54 57 59 60 63 64 65 66 90 93 94 97 98 76 78 79 82 83 84 72 51 56 58 61 34 39 86 42 91 95 81 77 80 62 67 88 70 92 52 85 89 75 96 41 27 69 55 99 28

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Vigenere Polyalphabetic Cipherj Vigeneres polyalphabetic cipher (19th century) generalizes

Caesars shift cipher Use keyword to select encrypting rowsVigenere TableauA B C D E F G H I J K L M N O P Q R S T U V W X Y Z J K L M N O P Q R S T U V W X Y Z A B C D E F G H I K L M N O P Q R S T U V W X Y Z A B C D E F G H I J L M N O P Q R S T U V W X Y Z A B C D E F G H I J K M N O P Q R S T U V W X Y Z A B C D E F G H I J K L N O P Q R S T U V W X Y Z A B C D E F G H I J K L M O P Q R S T U V W X Y Z A B C D E F G H I J K L M N P Q R S T U V W X Y Z A B C D E F G H I J K L M N O Q R S T U V W X Y Z A B C D E F G H I J K L M N O P R S T U V W X Y Z A B C D E F G H I J K L M N O P Q S T U V W X Y Z A B C D E F G H I J K L M N O P Q R T U V W X Y Z A B C D E F G H I J K L M N O P Q R S U V W X Y Z A B C D E F G H I J K L M N O P Q R S T V W X Y Z A B C D E F G H I J K L M N O P Q R S T U W X Y Z A B C D E F G H I J K L M N O P Q R S T U V X Y Z A B C D E F G H I J K L M N O P Q R S T U V W Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Z A B C D E F G H I J K L M N O P S R S T U V W X Y A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z B C D E F G H I J K L M N O P Q R S T U V W X Y Z A C D E F G H I J K L M N O P Q R S T U V W X Y Z A B D E F G H I J K L M N O P Q R S T U V W X Y Z A B C E F G H I J K L M N O P Q R S T U V W X Y Z A B C D F G H I J K L M N O P Q R S T U V W X Y Z A B C D E G H I J K L M N O P Q R S T U V W X Y Z A B C D E F H I J K L M N O P Q R S T U V W X Y Z A B C D E F G I J K L M N O P Q R S T U V W X Y Z A B C D E F G H

j The Vigenere cipher is

not amenable to simple frequency analysisj Actually invented earlier

(16th century)j Called The Unbreakable