Some block ciphers have been proposed for which the key size is approximately twice the block length. Examples in this class are FEAL-NX [228] (a FEAL version with a 128-bit key) and PES/IDEA [181, 182, 184]. Triple DES with 2 keys has a key size of 112 bits and a block length of 64 bits and could hence also be considered to belong to this class. Note that xDES1 discussed in section 5.3.2.2 is not of this type, as the key size is equal to 168 bits and the block length is 128 bits. Again one has to make a distinction between single and double length hash functions.
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