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Lecture 4:Lecture 4:

Message Confidentiality and Message Confidentiality and Message Integrity Message Integrity

Prof. Sead MufticProf. Sead Muftic

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Lecture 4 :Lecture 4 : Message Confidentiality and IntegrityMessage Confidentiality and Integrity

Subjects / Topics :Subjects / Topics :

1. Basic principles of message protection 1. Basic principles of message protection 2. Message confidentiality 2. Message confidentiality 3. Message integrity 3. Message integrity

S. Muftic Computer Networks SecurityS. Muftic Computer Networks Security 33

Lecture 4 :Lecture 4 : Message Confidentiality and IntegrityMessage Confidentiality and Integrity

Subjects / Topics :Subjects / Topics :

1. Basic principles of message protection1. Basic principles of message protection 2. Message confidentiality 2. Message confidentiality 3. Message integrity 3. Message integrity

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Some confidential text (message) in clear (readable) form

Network Aspects :Network Aspects : * selection of algorithms* selection of algorithms * format of messages * format of messages * message filtering * message filtering

Message ConfidentialityMessage Confidentiality

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Aspects :Aspects :

1. Algorithms: 3DES, 3DES-CBC, 1. Algorithms: 3DES, 3DES-CBC, IDEA, ...IDEA, ... 2. Mode, padding 2. Mode, padding 3. Filtering of cryptograms 3. Filtering of cryptograms 4. Integrity of cryptograms 4. Integrity of cryptograms 5. Exchange of keys5. Exchange of keys

Significant Aspects Significant Aspects

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Solutions (standards) :Solutions (standards) :

* algorithm: * algorithm: 3DES, AES3DES, AES * mode: * mode: CBCCBC, padding: , padding: Fx, …, FxFx, …, Fx * filtering of cryptograms: * filtering of cryptograms: base64base64 * integrity of cryptograms: * integrity of cryptograms: MD2MD2 * exchange of keys: * exchange of keys: KE protocolsKE protocols

Algorithms – Defaults Algorithms – Defaults

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AA BB

Alg-2Alg-1

Negotiation protocol

Algorithms – Negotiations Algorithms – Negotiations

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Algorithms – OIDsAlgorithms – OIDs

RC2-CBC OBJECT IDENTIFIER ::= {iso(1) member-body(2) US(840) rsadsi(113549) encryptionAlgorithm(3) 2}

1 2 840 113549 3 2

RC2 – CBC :RC2 – CBC :

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ENCRYPTED {ToBeEnciphered} ::= HASHED {ToBeHashed} ::=

BIT STRING (CONSTRAINED BY { OCTET STRING (CONSTRAINED BY {

-- must be the result of -- must be the result of -- applying an encipherment -- applying a hashing

-- procedure to the BER-encoded -- procedure to the DER-encoded

-- octects of the value of -- -- octetcs of the value --

ToBeEnciphered }) ToBeHashed })

SIGNATURE {OfSignature} ::=

SEQUENCE {

AlgorithmIdentifier,

ENCRYPTED {

HASHED {OfSignature}}}

Algorithms – Coding Algorithms – Coding

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Network Topology Network Topology

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Lecture 4 :Lecture 4 : Message Confidentiality and IntegrityMessage Confidentiality and Integrity

Subjects / Topics :Subjects / Topics :

1. Basic principles of message protection 1. Basic principles of message protection 2. Message confidentiality2. Message confidentiality 3. Message integrity 3. Message integrity

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MessageMessage

Encrypted messageEncrypted message

DESDES

8 8 8 8 8 8 8 8

KK KK KK KK

8 8 8 8 8 8 8 8

IVIV

Message Confidentiality – Encryption Message Confidentiality – Encryption

DESDES DESDES DESDES

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Message Confidentiality – CiphersMessage Confidentiality – Ciphers

Symmetric:

• DES• AES• 3DES• Blowfish / Twofish• IDEA• RC2• RC4• etc...

Asymmetric:

• RSA• Elliptic Curve• ElGamal

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Input messageInput message

Output message Output message 8 8 8 8 8 8 8 8

KK KK KK KK

8 8 8 8 8 8 5 5

IVIV

Message Confidentiality – Padding Message Confidentiality – Padding

DESDES DESDES DESDES DESDES

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Block Cipher Modes – Electronic Codebook (ECB)Block Cipher Modes – Electronic Codebook (ECB)

MessageMessage

Encrypted messageEncrypted message8 8 8 8 8 8 8 8

KK KK KK KK

8 8 8 8 8 8 8 8

DESDES DESDES DESDES DESDES

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Block Cipher Modes – Cipher Block Chaining (CBC)Block Cipher Modes – Cipher Block Chaining (CBC)

MessageMessage

Encrypted messageEncrypted message8 8 8 8 8 8 8 8

KK KK KK KK

8 8 8 8 8 8 8 8

IVIV

DESDES DESDES DESDES DESDES

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Block Cipher Modes – Cipher Feedback (CFB)Block Cipher Modes – Cipher Feedback (CFB)

MessageMessage

Encrypted messageEncrypted message8 8 8 8 8 8 8 8

8 8 8 8 8 8 8 8

IVIV DESDES

KK DESDES

KK DESDES

KK DESDES

KK

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Block Cipher Modes – Counter (CTR)Block Cipher Modes – Counter (CTR)

MessageMessage

Encrypted messageEncrypted message

8 8 8 8 8 8 8 8

DES

KK

8 8 8 8 8 8 8 8

DES

KK DES

KK DES

KK

nonce + counter

nonce + counter

nonce + counter

nonce + counter

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Message Confidentiality – Important ParametersMessage Confidentiality – Important Parameters

• Key• Algorithm• Padding Mode• Cipher Mode• IV• Nonce + Counter Initial Value

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Lecture 4 :Lecture 4 : Message Confidentiality and IntegrityMessage Confidentiality and Integrity

Subjects / Topics :Subjects / Topics :

1. Basic principles of message protection 1. Basic principles of message protection 2. Message confidentiality 2. Message confidentiality 3. Message integrity3. Message integrity

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Some confidential text (message) in clear (readable) form

E n c r y p t i o n E n c r y p t i o n

D e c r y p t i o n D e c r y p t i o n

Destruction of Cryptograms Destruction of Cryptograms

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Some confidential text (message) in clear (readable) form

1101 0011 1010 10011101 0011 1010 1001

MAC MAC

General Data IntegrityGeneral Data Integrity

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1101 0011 1010 10011101 0011 1010 1001

MAC MAC

Integrity of Cryptograms Integrity of Cryptograms

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MessageMessage

MACMAC

KK KK KK KK

8 8 8 8 8 8 8 8

IVIV

8 8 8 8 8 8 8 8

Hashing Algorithms Hashing Algorithms

DESDES DESDES DESDES DESDES

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AA BB

MAC

MACMAC

Verification Procedure Verification Procedure

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Message Authentication based on MAC Message Authentication based on MAC

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Some confidential

in clear (readable) form

1101 0011 1010 10011101 0011 1010 1001

MAC MAC

Modification of Message + Hash Modification of Message + Hash

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Some confidential

in clear (readable) form

1101 0011 1010 10011101 0011 1010 1001

MAC MAC

Prevention Prevention

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AA BB

Some confidential text (message) in clear (readable) form

MAC

Some confidential text (message) in clear (readable) form

MAC

MAC

Encryption of MAC Encryption of MAC

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Encryption of MAC – using Shared Secret Encryption of MAC – using Shared Secret

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Encryption of MAC – using Secret Key Encryption of MAC – using Secret Key

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Encryption of MAC – using Private Key Encryption of MAC – using Private Key

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Lecture 4 :Lecture 4 : Message Confidentiality and IntegrityMessage Confidentiality and Integrity

Subjects / Topics :Subjects / Topics :

1. Basic principles of message protection 1. Basic principles of message protection 2. Message confidentiality 2. Message confidentiality 3. Message integrity 3. Message integrity

S. Muftic Computer Networks SecurityS. Muftic Computer Networks Security 3434

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