ch4 3DES, AES, and Modes of Operation questions & answers graded A+

ch4 3DES, AES, and Modes of OperationMultiple Encryption - correct answer the process of encrypting an already encrypted message one or more times Double DES - correct answer The simplest form of multiple encryption has two encryption stages and two keys Given the potential vulnerability of DES to a brute-force attack, what are the alternatives? - correct answer - design a new algorithm AES for example - to use multiple encryption with DES and multiple keys. double DES strengths? - correct answer - more security (because of key length 112) double DES vulnerabilities ? - correct answer meet in the middle attack T of F: The use of double DES results in a mapping that is equivalent to a single DES encryption - correct answer False, not equivalent The meet-in-the-middle attack algorithm - correct answer will attack this scheme (DES) and does not depend on any particular property of DES but will work against any block encryption cipher Triple-DES with three-Keys - correct answer counter to the meet-in-the-middle attack is to use three stages of encryption with three different keys This raises the cost of the meet-in-the-middle attack to 2112, which is beyond what is practical Has the drawback of requiring a key length of 56 x 3 = 168 bits, which may be somewhat unwieldy As an alternative Tuchman proposed a triple encryption method that uses only two keys 3DES with two keys - correct answer is a relatively popular alternative to DES and has been adopted for use in the key management standards ANSI X9.17 and ISO 8732 use the algorithm of encrypt-dycript-encrypt Many researchers now feel that ........... is the preferred alternative - correct answer three-key 3DES Triple DES vulnerabilities? - correct answer slower to implement doesn't work good with large amount of data AES - correct answer 1. a symmetric block cipher intended to replace DES 2. block size of 128 bit 3. key size : 128, 192, 256 AES strengths - correct answer security strength equal to or better than 3DES and significantly improved efficiency. Modes of Operation - correct answer A technique for enhancing the effect of a cryptographic algorithm or adapting the algorithm for an application five modes of operation - correct answer 1. intended to cover a wide variety of applications of encryption for which a block cipher could be used 2. intended for use with any symmetric block cipher, including triple DES and AES Electronic Codebook (ECB) - correct answer Description: Each block of 64 plaintext bits is encoded independently using the same key. application: Secure transmission of single values (e.g., an encryption key)