Which
of the following encryption algorithms is used by the Clipper chip, which supports the escrowed
encryption standard?

A.
Skipjack

B.
Blowfish

C.
AES

D.
IDEA

Explanation:
Skipjack is a block cipher, an algorithm for encryption, which was initially developed by
the U.S. National Security Agency (NSA). Skipjack is an
encryption algorithm scheme of key escrow, and the cipher was provided for use in the Clipper chip,
implemented in tamperproof hardware.
Skipjack is used only for encryption; the key escrow is achieved through the use of a separate
mechanism known as the Law Enforcement

Access Field (LEAF). Skipjack uses an 80-bit key to encrypt or decrypt 64-bit data blocks. It is an
unbalanced Feistel network with 32 rounds. It
was specially designed to replace the Data Encryption Standard (DES).
Answer option C is incorrect. The Advanced Encryption Standard (AES) is an encryption standard
adopted by the U.S. government. The
standard comprises three block ciphers, AES-128, AES-192, and AES-256. Each AES cipher has a 128-
bit block size, with key sizes of 128, 192,
and 256 bits, respectively. The AES ciphers have been analyzed extensively and are now used
worldwide, as was the case with its
predecessor, the Data Encryption Standard (DES).
AES was announced by National Institute of Standards and Technology (NIST) as U.S. FIPS PUB 197
(FIPS 197) on November 26, 2001 after a
5-year standardization process in which fifteen competing designs were presented and evaluated
before Rijndael was selected as the most
suitable. It became effective as a standard on May 26, 2002. As of 2009, AES is one of the most
popular algorithms used in symmetric key
cryptography. It is available in many different encryption packages. AES is the first publicly accessible
and open cipher approved by the NSA for
top secret information.
Answer option B is incorrect. Blowfish is a symmetric 64-bit block cipher that can support key
lengths up to 448 bits. It is included in a large
number of cipher suites and encryption products. It was designed in 1993 by Bruce Schneier and is
freely available for anyone to use. This has
contributed to its popularity in cryptographic software.
Answer option D is incorrect. International Data Encryption Algorithm (IDEA) is a block cipher. IDEA
operates on 64-bit blocks using a 128-bit
key. This algorithm was intended as a replacement for the Data Encryption Standard. IDEA was used
in Pretty Good Privacy (PGP) v2.0, and
was incorporated after the original cipher used in v1.0 was found to be insecure. It is an optional
algorithm in OpenPGP. The cipher is
patented in a number of countries but is freely available for non-commercial use. IDEA is a minor
revision of an earlier cipher, PES (Proposed
Encryption Standard). It was originally known as IPES (Improved PES).