CIS
UVC2 STUDY MATERIAL.docx

# D identity verification an identity verification

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D. Identity verification - An Identity verification service is used by businesses to ensure that users or customers provide information that is associated with the identity of a real person. 5. Which activity is likely to be performed by an intruder watching a frequency analysis attack? In cryptanalysis, frequency analysis is the study of the frequency of letters or groups of letters in a cipher text. The method is used as an aid to breaking classical ciphers. A. Impersonating one of the intended participants in a conversation. B. Determining how frequently an attack is launched. C. Simultaneously scanning multiple radio frequency ranges. D. Identifying characters or symbols that appear most frequently in cipher text. 6. Which type of cipher applies mathematical functions to each bit individually? A. Block oriented - A block cipher algorithm is a basic building block for providing data security B. Permutation - A set of objects is an arrangement of those objects into a particular order. C. Stream - A stream cipher is a symmetric key cipher where plaintext digits are combined with a pseudorandom cipher digit stream (keystream). In a stream cipher each plaintext digit is

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encrypted one at a time with the corresponding digit of the keystream, to give a digit of the cipher text stream . D. Running key - In classical cryptography, the running key cipher is a type of polyalphabetic substitution cipher in which a text, typically from a book, is used to provide a very long keystream. Block versus Stream Cipher While both are symmetric ciphers, stream ciphers are based on generating an "infinite" Cryptographic keystream, and using that to encrypt one bit or byte at a time (similar to the one-time pad), whereas block ciphers work on larger chunks of data (i.e. blocks) at a time, often combining blocks for additional security (e.g. AES in CBC mode). •Stream ciphers are typically faster than block, but that has it's own price. •Block ciphers typically require more memory, since they work on larger chunks of data and often have "carry over" from previous blocks, whereas since stream ciphers work on only a few bits at a time they have relatively low memory requirements (and therefore cheaper to implement in limited scenarios such as embedded devices, firmware, and esp. hardware). •Stream ciphers are more difficult to implement correctly, and prone to weaknesses based on usage - since the principles are similar to one-time pad, the keystream has very strict requirements. On the other hand, that's usually the tricky part, and can be offloaded to e.g. an external box. •Because block ciphers encrypt a whole block at a time (and furthermore have "feedback" modes which are most recommended), they are more susceptible to noise in transmission, that is if you mess up one part of the data, all the rest is probably unrecoverable. Whereas with stream ciphers bytes are individually encrypted with no connection to other chunks of data (in most ciphers/modes), and often have support for interruptions on the line.
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