Exam 7: Block Cipher Operation

It is possible to convert a block cipher into a stream cipher using cipher feedback, output feedback and counter modes.

triple DES makes use of __________ stages of the DES algorithm, using a total of two or three distinct keys.

the plaintext of a sector or data unit is organized in to blocks of 128 bits.For encryption and decryption, each block is treated independently.the only exception occurs when the last block has less than 128 bits.In that case the last two blocks are encrypted/decrypted using a ___________ technique instead of padding.

__________ mode is suitable for parallel operation.Because there is no chaining, multiple blocks can be encrypted or decrypted simultaneously.Unlike CtR mode, this mode includes a nonce as well as a counter.

A __________ is a technique for enhancing the effect of a cryptographic algorithm or adapting the algorithm for an application, such as applying a block cipher to a sequence of data blocks or a data stream.

the __________ mode operates on full blocks of plaintext and ciphertext, as opposed to an s-bit subset.

OFB mode requires an initialization vector that must be unique to each execution of the encryption operation.

the __________ algorithm will work against any block encryption cipher and does not depend on any particular property of DES.

the simplest mode of operation is the ___________ mode, in which plaintext is handled one block at a time and each block of plaintext is encrypted using the same key.

the __________ standard describes a method of encryption for data stored in sector-based devices where the threat model includes possible access to stored data by the adversary.Some characteristics of this standard include: the ciphertext is freely available for an attacker, the data layout is not changed on the storage medium and in transit, and the same plaintext is encrypted to different ciphertexts at different locations.

Another important mode, XtS-AES, has been standardized by the __________ Security in Storage Working Group.

A number of Internet based applications have adopted two-key 3DES, including PGP and S/MIME.

the __________ block cipher mode of operation is a general purpose block oriented transmission useful for high speed requirements.

Once the plaintext is converted to ciphertext using the encryption algorithm the plaintext is then used as input and the algorithm is applied again.

there are no practical cryptanalytic attacks on 3DES.

"Input is processed s bits at a time.Preceding ciphertext is used as input to the encryption algorithm to produce pseudorandom output, which is XORed with plaintext to produce next unit of ciphertext", is a description of the _________ mode of operation.

A mode of operation is a technique for enhancing the effect of a cryptographic algorithm or adapting the algorithm for an application.

A typical application of Output Feedback mode is stream oriented transmission over noisy channel, such as satellite communication.

the most significant characteristic of __________ is that if the same b-bit block of plaintext appears more than once in the message, it always produces the same ciphertext.

"Each block of plaintext is XORed with an encrypted counter.the counter is incremented for each subsequent block", is a description of ___________ mode.