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31 Aug 16
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3.4. Why Three Encryption Techniques?
So, why are there so many different types of cryptographic schemes? Why can't we do everything we need with just one?
The answer is that each scheme is optimized for some specific application(s). Hash functions, for example, are well-suited for ensuring data integrity because any change made to the contents of a message will result in the receiver calculating a different hash value than the one placed in the transmission by the sender. Since it is highly unlikely that two different messages will yield the same hash value, data integrity is ensured to a high degree of confidence.
Secret key cryptography, on the other hand, is ideally suited to encrypting messages, thus providing privacy and confidentiality. The sender can generate a session key on a per-message basis to encrypt the message; the receiver, of course, needs the same session key to decrypt the message.
Key exchange, of course, is a key application of public-key cryptography (no pun intended). Asymmetric schemes can also be used for non-repudiation and user authentication; if the receiver can obtain the session key encrypted with the sender's private key, then only this sender could have sent the message. Public-key cryptography could, theoretically, also be used to encrypt messages although this is rarely done because secret-key cryptography operates about 1000 times faster than public-key cryptography.
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Privacy/confidentiality
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Integrity
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Non-repudiation
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symmetric encryption.
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stream ciphers
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block ciphers
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operate on a single bit (byte or computer word) at a time
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encrypts one block of data at a time using the same key on each block
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Self-synchronizing stream ciphers
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Synchronous stream ciphers
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Electronic Codebook (ECB)
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Cipher Block Chaining (CBC)
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Cipher Feedback (CFB)
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CFB mode allows data to be encrypted in units smaller than the block size
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Output Feedback (OFB)
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Data Encryption Standard (DES):
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56-bit key
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64-bit blocks
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three 56-bit keys
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Advanced Encryption Standard (AES)
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128, 192, or 256 bits
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128, 192, or 256 bits.
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one-way functions
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Multiplication vs. factorization
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Exponentiation vs. logarithms
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asymmetric cryptography.
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private key
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public key
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RSA: Th
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Digital Signature Algorithm (DSA)
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message digests
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one-way encryption
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digital fingerprint
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Message Digest (MD) algorithms
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128-bit
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byte-oriented
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Dubbed SHA-3
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hybrid cryptographic scheme
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Determining Strengths For Public Keys Used For Exchanging Symmetric Keys
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Certificates,
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Certificates
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Certificate Authorities (CA)
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Establish identity
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Assign authority
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Secure confidential information
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large prime number, n
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number g so that g<n
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two prime numbers, p and q
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n = pq.
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Select a third number, e
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d from the quotient (ed-1)/[(p-1)(q-1)]
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The minimum suggested RSA key is 1024 bits; 2048 and 3072 bits are even better.
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AES-128, AES-192, and AES-256
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Cryptography is the science of writing in secret code and is an ancient art; the first documented use of cryptography in writing dates back to circa 1900 B.C.
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Cryptography, then, not only protects data from theft or alteration, but can also be used for user authentication
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three types of cryptographic schemes typically used to accomplish these goals: secret key (or symmetric) cryptography, public-key (or asymmetric) cryptography, and hash functions, each of which is described below.
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With secret key cryptography, a single key is used for both encryption and decryption.
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Certificates and Certificate Authorities (CA) are necessary for widespread use of cryptography for e-commerce applications.
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As an example, 2 is not primitive to 7 because the set of powers of 2 from 1 to 6, mod 7 = {2,4,1,2,4,1}. On the other hand, 3 is primitive to 7 because the set of powers of 3 from 1 to 6, mod 7 = {3,2,6,4,5,1}.
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14 Dec 09
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Neal Aggarwalpaper very focused on terms, concepts, and schemes in current use
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01 Apr 09
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14 Mar 09
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Advanced Encryption Standard (AES): In 1997, NIST initiated a very publi
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07 Feb 09
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16 Dec 08
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09 Dec 08
Vipin ChandranA much shorter, edited version of this paper appears in the 1999 Edition of Handbook on Local Area Networks, published by Auerbach in September 1998. Since that time, this article has taken on a life of its own...
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07 Nov 06
Bernard NisetA much shorter, edited version of this paper appears in the 1999 Edition of Handbook on Local Area Networks, published by Auerbach in September 1998. Since that time, this article has taken on a life of its own...
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03 Nov 06
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25 Oct 06
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