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Module 22: Multi-core Computing Security
Lecture 44: Cryptography and ECB
The Lecture Contains:
Cryptography
Is Algorithm Secret?
Some Simple Ciphers
Breaking a Cipher Scheme
Secret Key Cryptography
Asymmetric Key Cryptography
Encrypting a Large Message
Threats on ECB
CBC Mode of Encryption
CBC Mode of Decryption
Threats on CBC Operation
PKI
Security Mechanism
Security Mechanism: Confidentiality
Security Mechanism: Integrity
Authentication: Symmetric Cipher Based
Owner Integrity: PKI
Authentication: PKI
Module 22: Multi-core Computing Security
Lecture 44: Cryptography and ECB
Cryptography
Cryptographers: (good guys) Invent clever algorithms Cryptanalysts: (bad guys) Attempt to break algorithms If lots of smart people have failed to solve a problem, then it probably won’t be solved, at least in near future. Cryptography systems depend upon computationally difficult problems which become simple when a secret (key) is known.
Is Algorithm Secret?
Some believe that keeping the algorithm secret enhances its security Some believe that publishing the algorithm will enhance the security. Difficult to keep the algorithm secret Common practice: Commercial algorithms are public while military applications keep it secret.
Module 22: Multi-core Computing Security
Lecture 44: Cryptography and ECB
Secret Key Cryptography
Also known as Symmetric Key Cryptography or conventional cryptography. The following is relevant Plaintext Encryption Algorithm Secret Key Decryption Algorithm Cipher-text Requirements Strong encryption algorithm (attackers may have access to the algorithm and a few cipher-text-plaintext pairs) Sender and receiver must have access to the secret key.
Module 22: Multi-core Computing Security
Lecture 44: Cryptography and ECB
Asymmetric Key Cryptography
Encrypting a Large Message
If the message is more than the size of the block, the message can be broken in multiple blocks. Let the message be known as concatenation of p1, p2, p3, …, pn. There are the following modes of operation Electronic Code Book (ECB) Cipher Block Chaining (CBC) Cipher Feedback Mode (CFB) Output Feedback Mode (OFB) Counter Mode (CTR)
Module 22: Multi-core Computing Security
Lecture 44: Cryptography and ECB
CBC Mode of Encryption
CBC Mode of Decryption
The receiver and sender must know key, and IV. Or key, and the method to compute IV.
Module 22: Multi-core Computing Security
Lecture 44: Cryptography and ECB
Threats on CBC Operation
Modification of cipher text blocks. Changing has predictable effect on. However, it also changes piin an unpredictable manner If the receiver is known to ignore pithen such attack is possible. Possible safeguard is to attach a checksum (such as CRC) to the message before encryption.
PKI
PKI Operations: Encryption, Decryption of short messages Digital signatures Authentication RSA: Uses modular exponents to make it computationally infeasible to recover message without key. Provided the message is carefully crafted. Keys are carefully selected.
Security Mechanism
Confidentiality Will an attacker make any sense out of a picked packet? Integrity Is the message unaltered? Owner Integrity Is the message really from that person? Authentication Is it you?
file:///D|/...ry,%20Dr.%20Sanjeev%20K%20Aggrwal%20&%20Dr.%20Rajat%20Moona/Multi-core_Architecture/lecture%2044/44_10.htm[6/14/2012 12:19:43 PM]
Module 22: Multi-core Computing Security
Lecture 44: Cryptography and ECB
Authentication: Symmetric Cipher Based
Challenge response Challenger sends a random number to the subject. Subject gives a response to the challenge Response derived using cryptography. For example, the encryption of the challenge using a shared key.
Owner Integrity: PKI
Digital Signature Can only be generated using the private key. Can be verified using the public key. Since private key is one person, Only the owner can generate it. A document may be hashed and the hash may be signed digitally by the owner of the private key. Any one can verify the sign. Must have access to the public key of the signer.
Authentication: PKI
Challenge-Response Challenger can ask the subject to sign a random number Challenger has access to the “certified” public key of the subject. Only subject can sign it correctly since it must have the access to the private key. Challenger can verify using public key.
