Plaintext

See, fot example, L. Slatet, Prozac Diary (New Yotk Random House, 1998) K. Jamison, An Unquiet Mind A Memoir of Moods and Madness (New Yotk Knopf, 1995) S. Kaysen, Girl, Interrupted (New Yotk Random House, 1993) S. Plath, The Bell Jar (New York Bantam, 1972) N. Maits, Plaintext Essays (Tucson, Ariz. University of Arizona Press, 1986) W. Styron, Darkness Visible A Memoir of Madness (New York Random House, 1990) E. Wurtzel, Prozac Nation (Boston, Mass. Houghton Mifflin Co., 1994). 

Cipher Series of transformations that converts plaintext to ciphertext using the Cipher... 

Keywords Cryptography block ciphers modes of operation Counter mode (CTR) known plaintext attacks gamma period gamma overlapping... 

The most effective classes of cryptanalytical attacks on block ciphers are known plaintext and chosen plaintext attacks. They assume that cryptanalyst knows the plaintext that corresponds to the intercepted cryptogram or can control the data input of the cipher respectively. As a result of this the security of block cipher-based stream cipher depends on both the block cipher security and the properties of the mode of operation scheme. 

According to the NIST Sp. Pub. N2800-38A [1], it is specified 5 modes of operation (and see also [2,3,4,5]). The first of them (ECB) is a pure block cipher all other modes define stream ciphers. Let s consider each of them and analyze the possibility to extract the base cipher input and output values from the known plaintext and cipher text. If this is possible for some mode then the class of known plaintext attacks is applicable to this mode. 

The next block of gamma is determined by one or a few of the preceding blocks of gamma. As we can see from the expressions the output of base cipher can be obtained as XOR of cryptogram and known plaintext blocks, but input of base cipher at current step equal to its previous output. 

Therefore, the OFB mode doesn t protect the base cipher from known plaintext attacks. 

Therefore, the CFB mode doesn t protect base cipher from the known plaintext attacks too. 

In the same way as the OFB mode, the base cipher output can be obtained as XOR of cryptogram and known plaintext. Its input values can t be obtained, but the differences between them are known and potentially it can be used for mounting some differential attack. Therefore, the Counter mode also doesn t protect base cipher from the known plaintext attacks. 

Now consider the ways of security improving of stream modes of operation. As was shown above the all standard modes of operation allow application of the known plaintext attack to their base block cipher. And also synchronous OFB mode doesn t guarantee the some lower bound of gamma s period. 

Shown scheme defines strengthened stream ciphering and authentication mode. This mode is similar to previous mode but has one distinction—the feedback value N, depends on the message block too. As a result the current internal state depends on all processed plaintext blocks. 

In standard modes of operation (excluding CTR) the base block cipher is vulnerable to known plaintext attacks. 

The Counter mode with session step weight value has increased security and can be recommended for encryption of information with the random access requirement and strict limitation to gamma overlapping in the case of multi-session key usage. Both proposed schemes of improved counter mode utilize dynamic step principle and protect base block cipher from known plaintexts and differential attacks. Their performance is practically equivalent to the performance of standard Counter mode with half block size output. The implementation of Dynamic Step Counter for 128-bit block-size requires about 10 non-paralleled micro operations on the 32-bit Intel Architecture (for comparison—the standard Counter mode requires 4 non-paralleled micro operations). 

Once the key has been safely delivered to the recipient and the plaintext has been encrypted any brute force attack on the cryptotext must deal with a huge number of possible keys. For example if the key has 128 binary digits the number of all possible keys is approximately 1038. 

Nostradamus snorted. But if I break the cipher, the plaintext would lead you back to Algol, almost certainly, and would also be admissible evidence. I shall do both. What else can you tell me How long has this Algol been operating What departments of government has he penetrated How does he... 

Excellent We ll make a scribe out of you yet. Now to begin the encipherment Under the first letter of the plaintexts, you see theV ofVIRTU, yes So you findS in the normal alphabet, the one that begins withA, and go down to the alphabet that begins withV and what letter do you find ... 

With surprisingly little help from me, Vasco managed to reverse the process and start recovering the original plaintext ... 

You will show Their Excellencies the restored plaintext Circospetto demanded acidly. 

The three chiefs were still muttering together, jabbing fingers at the plaintext. 

The simple Cardano form used by this Algol person is vulnerable, the Maestro said, rubbing salt in the wound. Had he followed the subtler recommendations of the sagacious Monsieur Vigenere and used the plaintext to encode itself, then even I might have failed to break it. As it is, I showed it all to Filiberto Vasco. He will explain the technique to you. He stretched his lips in a helpful smile. 

I do not know if Guarini then taught ciphering to Dolfin I suspect not. Dolfin had little privacy in that intimate family home, and the villains would feel safer if he just kept his plaintext notes in a safe place and handed them over to his weekly contact. Guarini enciphered them later, I think... but you can establish... 

The drawback of using an All-Or-Nothing mode is its latency, namely the entire message M must be decoded before the first block of plaintext is known. This makes the technique unusable for applications that cannot tolerate such latency. 

Interestingly, in terms of the broadcast length such system hardly increases the number of bits in the header as compared with a shared-key system - the only difference is g and the description of h. Therefore this difference is fixed and does not grow with the nmnber of revocations. Note however that the scheme as defined above is not immune to chosen-ciphertext attacks, but only to chosen plaintext ones. Coming up with public-key schemes where prefix-truncation is possible that are immune to chosen ciphertext attacks of either kind is an interesting challenge . 

Choose a message M as the challenge plaintext and a set 7Z of revoked users that must include all the ones it corrupted (but may contain more). 

The bases of the risk assessments, i.e., the assumptions which underlie the process, should be elucidated in plaintext (i.e., simple, straighforward common language) as much as possible. A special section in the risk assessment document should be written to comprehensively discuss the assumptions, and could also be in plaintext. 

Agency regulatory action - which can range from public education, warning labels, etc. to interdiction and total ban, with plaintext explanations of why the particular route was chosen ... 

The message that is to be sent is called the plaintext and the message in coded form is called the ciphertext. There are two main tasks involved in sending a coded message ... 

Taking the ciphertext message and obtaining the plaintext message from it. 

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