Module Four

N used in pgp n much more difficult than des rc5

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n Used in PGP n Much more difficult than DES RC5 – Family of algorithms n Developed by Ronald Rivest in 1994 n 32, 64 or 128 bit blocks, up to 0 to 255 rounds, 0 to 2048 bit keys n RSA patented in 1997 Public Key Cryptography n Employee private and public key n Public made available to anyone wanting to encrypt a message n Private key is used to decrypt n Public Key cannot decrypt the message it encrypted n Ideally private key cannot be derived from the public key n The other can decrypt a message encrypted by one of the keys n Private key is kept private n Possible through the application of one-way functions. Easy to compute in one direction but difficult to compute the other way n In order to be useful should have a trap door, a secret mechanism that enables you to accomplish the reverse function in a one way function n 1,000 to 10,000 times slower than secret key encryption n Hybrids use public key to encrypt the symmetric key
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n Important algorithms Diffie-Helllman RSA, El Gamal, Knapsack, Elliptic Curve RSA n Rivest, Shamir and Addleman n Based on difficulty of factoring a number which is the product of two large prime numbers, may be 200 digits each. n Can be used for Encryption, key exchange, and digital signatures Diffie-Hellman n Exchange secret keys over insecure medium without exposing keys n Without additional session key n Primarily key exchange El Gamal n Extended Diffie-Hellman to include signatures and encryption Merkle-Hellman Knapsack n Having set of items with fixed weights n Determining which items can be added in order to obtain a given total weight n Illustrated using Super increasing weights (all weights greater than sum of previous) Elliptic Curve n Elliptic curve discrete logarithm are hard to compute than general discrete logarithm n Smaller key size same level of security n Elliptic curve key of 160 bits = RSA of 1024 bits n Suited to smart cards and wireless devices (less memory and processing) n Digital signatures, encryption and key management Public Key Cryptosystem Algorithms n Factoring of Large Prime Numbers n RSA n Finding the discrete logarithm in a finite field n El Gamal n Diffie-Hellman n Shnorrs signature Algorithm n Elliptic Curve n Nybergrueppels signature algorithm Asymmetric and Symmetric Key Comparisons Asymmetric Key Symmetric Key 512 bits 64 bits 1792 bits 112 bits 2304 bits 128 bits Purpose of Digital Signatures n To detect unauthorized modifications and to authenticate identity and non-repudiation. n Generates block of data smaller than the original data n One way hash functions n One way has produces fixed size output (digest) n No two messages will have same digest n One way no getting original file from hash n Message digest should be calculated using all of original files data n After message digest is calculated it is encrypted with senders private key
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n Receiver decrypts using senders public key, if it opens then it is from the sender. n
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n Used in PGP n Much more difficult than DES RC5 Family of...

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