Bài giảng Computer Networks 1 (Mạng máy tính 1) - Lecture 11: Network Security - Phạm Trần Vũ
Lecture 11:
Network Security
Reference:
Chapter 8 - “Computer Networks”,
Hall, 2003.
2
Outline
ꢀ
Cryptography
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Introduction
Symmetric-key algorithms
Public-key algorithms
Digital Signatures
Management of Public Keys
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Apply to Computer Networks
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ꢁ
ꢁ
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Secure So
E-mail security
Web Security
3
Outline
ꢀ
Cryptography
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
Introduction
Symmetric-key algorithms
Public-key algorithms
Digital Signatures
Management of Public Keys
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Crytography(1)
ꢀ
Introduction
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Cryptography referred almost exclusively to encryption, the
process of converting ordinary information (plaintext) into
unintelligible gibberish (ciphertext)
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Crytography (2)
• Symmetric-key algorithms
– Encryption and decryption
functions that use the same
key are called symmetric
Encrypt
– In this case everyone wanting
to read encrypted data must
share the same key
– DES is an example of
symmetric-key algorithms
Decrypt
6
Crytography (3)
ꢀ
Data Encryption Standard
(a) General outline.
(b) Detail of one iteration. The circled + means exclusive OR.
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Crytography (4)
ꢀ Advanced Encryption Standard(AES)
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Rules for AES proposals
1. The algorithm must be a symmetric block cipher.
2. The full des
3. Key lengths of 128, 192, and 256 bits supported.
nondiscriminatory terms.
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Crytography (5)
ꢀ
Some common symmetric-key cryptographic algorithms
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Crytography (6)
ꢀ
Public-Key Algorithms
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So is called Asymmetric-key Algorithms
Based on some hard problems such as integer factoring, …
When data yiother key must be
used to decrypt the data, and vice versa.
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key
Public key is
Priva
given away to
known only to
the world
owner
10
Crytography (7)
ꢀ
RSA(Rivest, Shamir, Adleman)
ꢁ
Choose two large primes, p and q (typically 1024 bits).
Compute n = p x q and z = (p - 1) x (q - 1).
Choose a number relatively prime to z and call it d.
Find e such that e x d = 1 mod z.
Pair key: {(e, n), (d,n)}
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Example
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p = 3, q = 11 -> n = 33, z = 20
Choose
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e = 3
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Crytography (8)
ꢀ
RSA(Rivest, Shamir, Adleman)
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Crytography (9)
ꢀ
Digital Signatures
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Digital signatures allow the world
to verify I created a hunk of data
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e.g. email, code
Sign
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Digital signatures are created by
encrypting a hash of the data with
my private key
Encrypt
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The resulting encrypted data is the
signature
This hash can then only be
decrypted by my public key
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Crytography (10)
ꢀ
Digital Signatures
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Verify
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Given some data with my signature, if you decrypt a
signaturash of the data,
you know it was encrypted with my private key
Hash
=?
Decrypt
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Crytography (12)
• Management of Public keys
– By checking the signature, one can determine that a
public key belongs to a given user.
Hash
Subject
Public Key
Issuer
=?
Decrypt
Signature
Public Key from
Issuer
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Crytography (13)
• Public-Key Infrastructure (PKI)
(a) A hierarchical PKI. (b) A chain of certificates.
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Outline
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Apply to Computer Networks
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Terms
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Authentication
Authorization
Message Protection
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Secure Sockets Layer (SSL)
E-mail security
Web Security
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Apply to Computer Networks(1)
• Authentication
– Verification of identity.
– Many mechanisms exist:
• Username/password
• Kerberos
• Public key Cryptography
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Apply to Computer Networks(2)
• Authentication
– Authentication Using Public-Key Cryptography
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