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"Secret code" redirects here. For the Aya Kamiki album, see Secret Code."Cryptology" redirects here. For the David S. Ware album, see Cryptology (album).German Lorenz cipher machine, used in World War II to encrypt very-high-level general staff messagesCryptography (or cryptology; from Greek κρυπτός kryptós, "hidden, secret"; and γράφειν graphein, "writing", or -λογία -logia, "study", respectively)[1] is the practice and study of techniques for secure communication in the presence of third parties (called adversaries).[2] More generally, it is about constructing and analyzing protocols that block adversaries;[3] various aspects in information security such as data confidentiality, data integrity, authentication, and non-repudiation[4] are central to modern cryptography. Modern cryptography exists at the intersection of the disciplines of mathematics, computer science, and electrical engineering. Applications of cryptography include ATM cards, computer passwords, and electronic commerce.Cryptography prior to the modern age was effectively synonymous with encryption, the conversion of information from a readable state to apparent nonsense. The originator of an encrypted message shared the decoding technique needed to recover the original information only with intended recipients, thereby precluding unwanted persons to do the same. Since World War I and the advent of the computer, the methods used to carry out cryptology have become increasingly complex and its application more widespread.Modern cryptography is heavily based on mathematical theory and computer science practice; cryptographic algorithms are designed around computational hardness assumptions, making such algorithms hard to break in practice by any adversary. It is theoretically possible to break such a system, but it is infeasible to do so by any known practical means. These schemes are therefore termed computationally secure; theoretical advances, e.g., improvements in integer factorization algorithms, and faster computing technology require these solutions to be continually adapted. There exist information-theoretically secure schemes that provably cannot be broken even with unlimited computing power—an example is the one-time pad—but these schemes are more difficult to implement than the best theoretically breakable but computationally secure mechanisms.Cryptology-related technology has raised a number of legal issues. In the United Kingdom, additions to the Regulation of Investigatory Powers Act 2000 require a suspected criminal to hand over his or her decryption key if asked by law enforcement. Otherwise the user will face a criminal charge.[5] The Electronic Frontier Foundation (EFF) was involved in a case in the United States which questioned whether requiring suspected criminals to provide their decryption keys to law enforcement is unconstitutional. The EFF argued that this is a violation of the right of not being forced to incriminate oneself, as given in the fifth amendment.[6]

TRANSCRIPT

  • Cryptographic

    Algorithms

    14th May 2012

    P.R.Lakshmi Eswari

    e-Security Team

    C-DAC Hyderabad

  • Network Security

    What is it ?

    Why do we need it ?

    How is it provided ?

  • Normal Flow

    Network Security Issues

  • Normal Flow

    Interruption

    Network Security Issues

  • Normal Flow

    Modification

    Interruption

    Network Security Issues

  • Normal Flow

    Modification Interception

    Interruption

    Network Security Issues

  • Normal Flow

    Fabrication

    Modification Interception

    Interruption

    Network Security Issues

  • Normal Flow

    Fabrication

    Modification Interception

    Interruption

    Get it?

    Repudiation

    No!

    No!

    Sent it?

    Network Security Issues

  • Requirement

    Fabrication

    Modification Interception

    Get it?

    Repudiation

    No!

    No!

    Sent it?

    Availability

    Network Security Services

  • Requirement

    Fabrication

    Interception

    Get it?

    Repudiation

    No!

    No!

    Sent it?

    Availability

    Integrity

    Network Security Services

  • Requirement

    Fabrication

    Get it?

    Repudiation

    No!

    No!

    Sent it?

    Availability

    Integrity Confidentiality

    Network Security Services

  • Requirement

    Get it?

    Repudiation

    No!

    No!

    Sent it?

    Availability

    Integrity Confidentiality

    Authenticity

    Network Security Services

  • Requirement

    Availability

    Integrity Confidentiality

    Authenticity Non Repudiation

    Network Security Services

  • Security Mechanisms

    Confidentiality - Encryption

    Integrity - Hashing

    Authentication - Digital Certificates

    Non-Repudiation - Digital Signatures

  • Cryptographic Algorithms

    Types of Cryptographic algorithms

    Secret key cryptography or Symmetric Key

    Public key cryptography or Asymmetric Key

    Hash functions

  • Symmetric Cryptography

  • Asymmetric Cryptography

  • Types of Cryptosystems

    Secret Key or Symmetric Cryptography

    DES, IDEA, AES etc

    Advantages: fast, cipher text secure

    Disadvantages: must distribute key in advance, key must not be divulged

    Public-key or Asymmetric Cryptography

    RSA, Diffie-Hellman key agreement protocol etc Advantages: public key widely distributable, does digital

    signatures

    Disadvantages: slow

  • Secret Key Algorithms

    Encryption

    algorithm

    Decryption

    algorithm

    Shared Secret Key

    Plain text

    input

    Plain text

    output Transmitted

    Cipher text

    Confidentiality

  • Secret Key Encryption

    Block Cipher: Operates on a block of

    message or plaintext at a time

    Ex: DES, IDEA)

    Types

  • Data Encryption Standard (DES)

    Permutation

    Permutation

    Swap

    Round 1

    Round 2

    Round 16

    Generate keys

    Initial Permutation

    48-bit K1

    48-bit K2

    48-bit K16

    Swap 32-bit halves

    Final Permutation

    64-bit Output

    48-bit K1 64-bit Input 56-bit Key

  • Triple DES

    Uses 3 keys and 3 executions of DES algorithm.

    Encrypt

    Encryption

    Decryption

    Decrypt Encrypt

    Decrypt Encrypt Decrypt

    Plain

    text

    Cipher

    text

    Cipher

    text Plain

    text

    Key1 Key2 Key3

    Key3 Key2 Key1

    Secret Key Encryption

  • Other Secret key algorithms

    IDEA (International Data Encryption Algorithm)

    128 bit key, 8 rounds

    Blowfish

    Variable key length. (up to 448 bits). Generally 128 bit key used. 16 rounds.

    Easy to implement and high execution speed.

    Secret Key Encryption

  • Other Secret key algorithms

    CAST 128

    Key size between 40 and 128 bits.

    F varies from round to round.

    AES (Advanced Encryption Standard)

    Variable block length (128, 192, 256 bits)

    Variable key length (128, 192, 256 bits)

    Ease of implementation in software and hardware.

    Secret Key Encryption

  • Stream Cipher

    A pseudo random no. generator

    continuously generates bits known as

    running key or keystream.

    xoring the keystream to the plain text

    produces the cipher text.

    e.g. RC4, SEAL, A5/1 (used in GSM)

    Secret Key Encryption

  • Stream Cipher

    Keystream

    generator +

    + Keystream generator

    key

    key

    plaintext

    ciphertext

    plaintext

    ciphertext

    Encryption

    Decryption

    Keystream Generator is a pseudo random generator like linear feedback shift register

    Secret Key Encryption

  • Key Distribution

    Symmetric schemes require both parties to

    share a common secret key

    Issue is how to securely distribute this key

    Often secure system failure due to a break in

    the key distribution scheme

  • Public Key Cryptography

    Uses two keys: private & public

    Used for

    Confidentiality

    Authentication

    Key distribution

  • The sender encrypts using public key of

    receiver

    Only the receiver can decrypt the cipher

    message with his private key

    Public Key Cryptography

    Confidentiality

  • Public Key Algorithms

    Encryption

    algorithm

    Decryption

    algorithm

    Plain text

    input

    Plain text

    output

    Transmitted

    Cipher text

    Private Key

    Public key ring

    Confidentiality

  • RSA

    Key Generation

    Calculate n = p x q

    Calculate (n) = (p-1)(q-1)

    Select integer e such that e is relatively

    prime to (n)

    Calculate d = e-1mod (n)

    (d = multiplicative inverse of e)

    Public Key = {e, n} Private Key = {d, n}

    Public Key Cryptography

  • Encryption

    Plaintext M < n

    Cipher text C = Me(mod n)

    Decryption

    Cipher text C

    Plaintext M = Cd(mod n)

    Public Key Cryptography

    RSA

  • Strength of Cryptographic Algorithms

    Identify the weakest links

    Key length: key can be broken by brute force attack.

    For a 32 bit key max. possible combinations is 232.

    Hence size of key is crucial.

    Symmetric algorithms: key sizes currently used is 128 bits

    Public key algorithms: require much larger key sizes since

    an extra structure i.e. public key is available to

    cryptanalyst. Hence keys with 1024 bits and more are

    safer.

    Cryptography

  • Public Key Algorithms

    Encryption

    algorithm

    Decryption

    algorithm

    Plain text

    input

    Plain text

    output

    Transmitted

    Cipher text

    Private Key

    Public key ring

    Authentication

  • Public Key Algorithms

    Encryption

    algorithm

    Decryption

    algorithm

    encrypted

    key

    Private Key

    Session

    key

    Shared

    session

    key

    Public key ring

    Key Exchange

  • Enables 2 users to exchange a secret key

    securely that can be used for subsequent

    encryption of messages.

    If p is prime no., its primitive root a is such

    that a mod p, a2 p-1 mod p are

    distinct integers from 1 to p-1 in some

    permutation.

    Key Management

    Diffie-Hellman Key Exchange

  • Diffie Hellman key exchange

    User A User B

    prime p

    Public key

    pk1 = xmod p

    Public key

    pk2 = ymod p

    pk1 pk2

    Public Key Cryptography

    random no. x random no. y

    Secret Key

    K = pk2xmod p

    = xymod p

    Secret Key

    K = pk1ymod p

    = xymod p

    primitive root

    prime p

    primitive root


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