ENCRYPTION

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ENCRYPTION
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ENCRYTION

• ENCRYPTION
• CONVERTING PLAINTEXT TO CIPHERTEXT
• DECRYPTION

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STREAM VS. BLOCK

• STREAM CIPHER EACH CHARACTER IS ENCRYPTED
• BLOCKCIPHER EACH CHARACTER IS ENCRYPTED

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KEY

• MATHEMATICAL TECHNIQUE TO ENCRPT
• (IF YOU LOOKED AT A KEY -- YOU WILL SEE A SET OF
  NUMBERS)

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SINGLE KEY

• SAME KEY USED TO CRYPT AND DECRYPT
• SYMMETRIC KEY
• SECRET KEY / PRIVATE KEY

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DUAL KEY

• PRIVATE KEY KEPT WITH OWNER OF KEY
• PUBLIC KEY IN PUBLIC PLACE AND ACCESSED BY
  ANYONE
• ENCRYPT WITH ONE AND DECRYPT WITH THE OTHER.

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KEY CHARACTERISTICS

• SPEED
• ENCRYPTION / DECRYPTION HAS TO BE FAST
• KEY DISTRIBUTION / SAFETY
• MUST BE ABLE TO DISTRIBUTE KEY WITHOUT IT BEING
  STOLEN
• TAMPERING WITH KEY

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PRIVATE KEY

• SINGLE KEY -- FASTER (GENERALLY), SPEED OF
  HARDWARE MAKES THIS CRITERION LESS IMPORTANT
• SINGLE KEY -- KEY EXCHANGE IS MORE DIFFICULT
  OFFLINE EXCHANGE
• FREQUENT EXCHANGE IS A PROBLEM

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DUAL KEY

• SLOWER
• BUT PUBLIC KEY IS FREELY AVAILABLE, NO KEY
  EXCHANGE.
• DANGER OF PUBLIC KEY BEING TAMPERED WITH.

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ISSUES ADDRESSED

• PRIVACY
• AUTHENTICITY
• SIGNATURE
• DOCUMENT
• CERTIFICATION
• ELECTRONIC PAYMENT SYSTEMS

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PRIVACY

• IF WE WANT ONLY RECEIVER TO SEE THE DOCUMENT
• SINGLE KEY
• ONLY RECEIVER WILL HAVE KEY.
• DUAL KEY
• ENCRYPT WITH RECEIVER PUBLIC KEY
• ONLY RECEIVER HAS PRIVATE KEY

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EXAMPLES OF KEY SYSTEMS

• SINGLE
• DATA ENCRYPTION STANDARDS(DES)
• INTERNATIONAL DATA ENCRYPTION ALGORITHMM
• DUAL
• RSA (RIVEST SHAMIR ADELMAN)

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DES

• 64-BIT BLOCKS
• 56-BIT KEY
• THE LARGER THE SIZE OF THE KEY, THE MORE
  DIFFICULT IT IS TO BREAK
• U.S. GOVT HAS LIMITATIONS ON KEY TECHNOLOGY THAT
  MAY BE EXPORTED.
• (USED TO BE 40-BIT NOW??)

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IDEA

• 64-BIT BLOCK
• 128-BIT KEY
• ALGORITHM TO GENERATE KEY IS READILY AVAILABLE
• OUTSIDE U.S. REGULATIONS, BECAUSE INTERNATIONAL
  STANDARD

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ENHANCING SECURITY

• APPLY KEY MULTIPLE TIMES

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RSA

• BLOCK CIPHERS
• VARIABLE BIT SIZE
• RC2 -- UPTO 40-BIT
• RC5 -- UPTO 2048 BITS
• BUT SLOWER THAN DES

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RSA DIGITAL ENVELOPE

• TO GET SPEED OF DES
• BUT FLEXIBILITY OF RSA KEY DISTRIBUTION.
• STEP 1
• USE DES TO ENCRYPT MESSAGE
• RECEIVER DOES NOT HAVE DES KEY

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RSA DIGITAL ENVELOPE

• STEP 2
• USE RSA PUBLIC KEY OF RECEIVER TO ENCRYPT DES
  KEY
• ONLY RECEIVER HAS PRIVATE KEY TO DECIPHER

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RSA DIGITAL ENVELOPE

• SPEED
• RSA SLOW, BUT AMOUNT OF INFO IN DES KEY IS
  LITTLE, SO NOT AN ISSUE
• DES IS FAST, MESSAGE IS LARGE -- SO YOU NEED A
  FAST KEY

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AUTHENTICITY

• IS SIGNATURE AUTHENTIC?
• IS DOCUMENT AUTHENTIC AND UNALTERED?

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DIGITAL SIGNATURE

• PART OR ALL OF DOCUMENT IS ENCRYPTED WITH
  SENDER PRIVATE KEY.
• ONLY SENDER SHOULD HAVE ACCESS TO IT.
• SO.. ONE CAN THINK OF THAT AS A SIGNATURE

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BUT..

• A) LEGALLY, THIS HAS TO BE ACCEPTED AS A
  SIGNATURE
• B) STANDARD HAS TO BE AGREED ON.
• GOVT COMING UP WITH STANDARD
• PROPOSING DIGITAL SIGNATURE ALGORITHM (MUCH
  DISPUTE)

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ISSUES

• A) ORGANIZATIONS STANDARDIZED ON RSA
• B) DSA -- FAST ON SIGNING, SLOW ON VERIFICATION
  RSA IS REVERSE..
• C) DSA UNPROVEN

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DOCUMENT AUTHENTICATION

• ONE-WAY HASH ALGORITHM APPLIED TO DOCUMENT
• RESULT DIGEST-1
• DOCUMENT DIGEST-1 SENT.
• RECEIVER APPLIES SAME HASH ALGORITHM TO DOCUMENT
• RESULT DIGEST-2

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DOCUMENT AUTHENTICATION

• IF DIGEST-1 DIGEST-2, THEN DOCUMENT UNALTERED.
• IF NOT, DOCUMENT ALTERED. MUST RE-TRANSMIT.

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SUMMARY

• SINGLE-KEY, DUAL KEY
• USED FOR
• PRIVACY
• AUTHENTICATION
• SIGNATURE
• DOCUMENT
• POSSIBLE TO COMBINE