3. Introduction
• Cryptography
– Confidentiality: keep information secret
– Authentication: legitimate author/user?
– Integrity: Is the data compromised?
– Non-repudiation: Protect denial
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4. Introduction
• Cryptography
– Encryption/Decryption: make a cryptogram
for the unauthorized not be able to figure
out the data
– Hash (Message Digest): digest a message
into a fixed length hash value, no key is
needed
– MAC (Massage Authentication Code): make
a fixed length MAC value, key is needed
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5. Introduction
• Symmetric Algorithm
– Same key (Symmetric Key) is used for
encryption and decryption
– Example: DES, AES
– Easier and faster than asymmetric algorithm
– Must transfer key in secure manner
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6. Introduction
• Asymmetric Algorithm
– Different keys (Asymmetric Key) are used
– Key pairs (private/public keys) are
mathematically linked
– Example: RSA
– Harder and slower than symmetric algorithm
– No need to transfer decryption key
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7. Fixed Key
• Physically load a key (fixed) to the client
• The client encrypt a data with the key
• The host decrypt the data with the key
• The key is replaced on either plan or key
compromise
• Same key is used over and over for
encipherment
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9. Master / Session Key
• Share a master key between host and
client beforehand
• Host generates a session key before
transaction
• Host encrypts the session key with the
master key and send to client
• Client decrypts the encrypted session
key with the master key shared
beforehand
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10. Master / Session Key
• Must generate and share a new master
key if the master key is compromised
• Still popular because of effectiveness
• Adoption of asymmetric for master key
• Developed before asymmetric algorithm
was developed
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11. Master / Session Key
PRIVATEPUBLIC
Host Client (device)
Generate asymmetric key pair and tra
nsfer private key to client at factory
Symmetric Key
PRIVATE
Encrypted
Symmetric Key
Encrypted
Symmetric Key
encryption decryption
Symmetric Key
Network
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12. Master / Session Key
Host Client (device)
Data encryption and decryption with
symmetric key
Data
encryption
Data
Network
Data Data
decryption
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13. DUKPT
• Derived Unique Key Per Transaction
• Host has BDK (Base Derivation Key) and
generates IPEK (Initial Pin Encryption Key)
• IPEK is inserted into client
• Client generates Future Key sets and
remove IPEK
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14. DUKPT
• Future Key is used for data encryption
• The used future key is replaced with a
newly generated future key
• Client transmits key set id, client id and
transaction counter with encrypted data
• Host calculates the encryption key with
the transmitted data and decrypt
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17. Closing
• Key managements are not limited with
these three ways – can be used mingled
• The devices should be tamper proof
• Reference: ANS X9.24-1
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