Key length

Two major sources of vibration due to mechanical imbalance in equipment with rotating parts or rotors are (1) assembly errors and (2) incorrect key length guesses during balancing. 

With a keyed-shaft rotor, the balancing process can introduce machine vibration if the assumed key length is different from the length of the one used during operation. Such an imbalance usually results in a mediocre or good running machine as opposed to a very smooth running machine. 

When balancing a keyed-shaft rotor, one half of the key s weight is assumed part of the shaft s male portion. The other half is considered part of the female portion that is coupled to it. However, when the two rotor parts are sent to a balancing shop for re-balancing, the actual key is rarely included. As a result, the balance operator usually guesses at the key s length, makes up a half key, and then balances the part. (Note A half key is of full-key length, but only half-key depth.)... 

In order to prevent an imbalance from occurring, do not allow the balance operator to guess the key length. It is strongly suggested that the actual key length be recorded on a tag that is attached to the rotor to be balanced. The tag should be attached in such a way that another device (such as a coupling half, pulley, fan, etc.) cannot be attached until the balance operator removes the tag. 

The effective key length, L is that portion of key having full bearing on hub and shaft. Note that the curved portion of the keyseat made with a rotary cutter does not provide full key bearing, so L does not include this distance. The use of an end mill cutter results in a square-ended keyseat. 

Fig. 1.16 Graphical representation of the fence model, with the key length (Aj ) and height (Ajj) parameters...

Less than 7 months. Read the note for 512-bit key length... 

The key length, in bits, determines the encryption strength of the cryptographic algorithm. Refer to Table 24-1. For example, DES, which was adopted in 1977, uses a 56-bit key length and can be cracked by specialized computers in only a few hours. In addition, the use of DES is not recommended due to the susceptibility to cryptographic exhaustion attack. One replacement for DES, is Triple DES which uses two 56-bit keys. 

Different scale features give different scale properties. At the smallest level, the lattice parameter is a key length scale parameter for atomistic simulations. Since atomic rearrangement is intimately related to various types of dislocations, Orowan [88], Taylor [89], Polyani [90], and Nabarro [91] developed a relationship for dislocations that related stress to the inverse of a length scale parameter, the... 

A similar work for authentication schemes was only published 15 years later In [GiMS74], the information-theoretic, i.e., absolute security of symmetric authentication schemes was defined. Schemes complying with this definition are often called authentication codes. Like Claude Shannon s work, [GiMS74] already contains both concrete constructions of authentication codes and lower bounds on the achievable efficiency, and in particular, the key length. In contrast to secrecy schemes, however, the upper and lower bounds are not identical furthermore, the constructions are less trivial. Therefore, there has been further research in this field. 

In particular, efficiently computable authentication codes where the key length only grows logarithmically with the length of the messages to be authenticated later were constructed in [WeCaSl]. An improvement of this scheme and an overview of the literature in this field can be found in [BJKS94]. 

Recall from Remark 10.24 that a scheihe exists where the key length and the private storage are the same as in Construction 10.22 and the signature length is only Ik, but that it has disadvantages in other respects and log2(A0 must be dominated by k in these schemes anyway. 

Although the key length of DES is now short enough to be susceptible to brute force attacks, there are variants of DES that effectively have a longer key length. It is important to note that even though these constructions are more resistant to brute force attacks, it is theoretically possible that they are more susceptible to structural attacks. However, no structural attacks are known on the two constructions presented here that are more efficient than structural attacks on DES itself. 

The reason for the encrypt/decrypt/encrypt pattern is for compatibility with regular DES triple-DES with Ki = K2 is identical to regular DES. With independently chosen keys, triple-DES has an effective key length of 128 bits. 

Even at the time of DES s standardization, there was some concern expressed about the relatively short key length, which was shortened from IBM s original proposal. Given a ciphertext/plaintext pair, or from several ciphertexts and a notion of a meaningful message, a brute force attack... 

The Rijndael algorithm supports a variable key size and variable block size of 128,192, or 256 bits, but the standard is expected to allow only block size 128, and key size 128, 192, or 256. Rijndael proceeds in rounds. For a 128-bit block, the total number of rounds performed is 10 if the key length is 128 bits, 12 if the key length is 192 bits, and 14 if the key length is 256 bits. 

For example, a good vibration level that can be obtained without following the precautions described in this section is amplitude of 0.12 inches/second (3.0 mm/sec.). By following the precautions, the orbit can be reduced to about 0.04 in./sec. (1 mm/sec.). This smaller orbit results in longer bearing or seal life, which is worth the effort required to make sure that the proper key length is used. 

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