Encryption

“ The state space is an addition on a standard encryption scheme and will allow these features to exist. As described in regards to Signal’s Double Ratchet step, this state can include information about the chain of derived keys or the new Diffie-Hellman key information. In the case of a tree structure, the state might represent the current values and nodes of the tree structure. The state could at its simplest be a simple counter of natural numbers counting the number of total messages sent between Alice and Bob. ”

“ Key Encapsulation Method Key encapsulation refers to the encapsulation of a key inside of a public/private key structure. Let be a key in the symmetric key space which Alice wants to post to other people in a secure way. Then, using public-key private key cryptography (and any algorithm of choice of a public key system) , Alice can transmit this key securely to another member. However, in a group setting, Alice needs to encrypt the key separately for each member. If Alice then wants to use a new encryption key, she needs again to re-encrypt the key separately for each member. ”

“ At the same time, democratic activists in the former Soviet Union would be able protect their messages if tyranny returns.
The name for this encryption package was PGP and by 1995 it was as much a cause as a program. Thousands had downloaded it off the Internet and other networks. Named in tribute to Ralph’s Pretty Good Grocery on Garrison Keillor’s radio show, PGP stood for Pretty Good Privacy. PGP lived up to its name—people needed it. Part of the reason was the nature of the Net itself. A skilled hacker could intercept unencrypted e-mail more easily than on the regular commercial networks. ”

“ In ElGamal encryption, as done in most public key cryptography encryption schemes, a symmetric key is established and then proceeding communication can occur using a symmetric-key based algorithm such as . ”

“ Namely, suppose that each time Alice sent Bob an encrypted message, Bob then generated a new public-key pair, replied to Alice with his new public key, and the next message from Alice to him would use the new public key. In this fashion, even if the first 3 messages get compromised, any new messages would still be secured (break-in recovery) ; and if today’s key was compromised, all the old messages were encrypted with old keys that may have been deleted by now (forward secrecy) . Each generation of a new public-key pair would be considered a ratchet step. ”

“ The probability that the adversary guesses correctly minus the probability the adversary guesses wrong, which is the adversary advantage, should be (negligibly) zero. Let be the event that the adversary guesses correctly and be the event that the adversary guesses wrongly.
Definition 2. Break-in recovery:
Break-in recovery is defined by a near equivalent game. The challenger picks a random message , and an initial key . The challenger initializes the state and then computes the cipher and sends to the adversary . As part of the encryption output the challenger is also left with a new state . ”

“ The weak form of encryption employed by CSS led some cryptographic experts to express skepticism as to “ [w] hether CSS is a serious cryptographic cipher. . . .” Frank A. Stevenson, Cryptanalysis of Contents Scrambling System (Nov. 8, 1999) , http://www.cs.cmu.edu/~dst/DeCSS/FrankStevenson/analysis.html. ↑ See Reimerdes, 111 F. Supp. 2d at 310-11 & n.60; see also DVD Copy Control Ass’n Inc. v. Bunner, 10 Cal. Rptr. 3d 185, 188 (Cal. Ct. App. 2004) (explaining content industry’s reliance on exclusive licensing scheme to limit dissemination of decryption keys) . ↑ See Reimerdes, 111 F. Supp. ”

“ Let be a group with generator used for public-key cryptography. Let be a key encapsulation method which takes a value in some space and outputs a private-public key pair of elements in the group . Then,
Where is a private key, is a public key, and is optional ciphertext in the ciphertext space containing securely encrypted information about . ”

“ The problem of "which nodes need to receive encrypted values", or as I wrote earlier, computing "the least number of common ancestors whom if they had the new values would ensure that all group members can reach the root" is quite a simple one. Since each node’s value is the hash of only one of two children, then the child that was not used to generate the parent is the one that no longer shares knowledge of the root key. ”

“ Understandably Baker began by denying that Clipper would “create a brave new world of government intrusion into the privacy of Americans.” Baker said that key escrow would merely maintain Washington’s rights to do wire-taps as presently authorized. That was a wrong; the government actually was going out of its way to make us all tap ready, as if we were back in the old Soviet Union in the KGB era. But at least in this case Baker wasn’t maligning the Net. The nastiness oozed out later when his article took on “Myth Number Two: Unreadable encryption is the key to our future liberty.” ”

“ The Clinton Administration wanted to license Clipper to the private sector, where it would show up in millions of telephones and dominate the market—displacing future encryption schemes based on technologies such as PGP. Washington hoped to make Clipper too cheap to resist and to provide a federal market for Clipper products. AT&T and the rest could put Clipper in telephones, and then, supposedly, dope peddlers couldn’t peddle and terrorists couldn’t terrorize without the Feds having a chance to intercept their conversations. The government would also work to make computers snoop friendly. ”

“ Enter keys: a cipher that uses a key is still more secure. Even if the cipher is disclosed, even if the ciphertext is intercepted, without the key (or a break) , the message is secret. Post-war, this is doubly important as we begin to realize what I think of as Schneier's Law: "any person can invent a security system so clever that she or he can't think of how to break it." This means that the only experimental methodology for discovering if you've made mistakes in your cipher is to tell all the smart people you can about it and ask them to think of ways to break it. ”

“ Even a basically weak cipher, in the hands of an expert, can be made to serve its purpose; and the strongest can be made useless when improperly used.
In the present text, we are likely to be found looking at ciphers largely from a military angle, which, apparently, has a more general interest than any other. In time of war, the cryptographic service, that is, the encipherment and transmitting service, is suddenly expanded to include a large number of new men, many of whom know nothing whatever of cryptanalysis, or the science of decryptment. ”

“ Even book cipher, notably secure, however unwieldy in use, has been decrypted because of the encipherer’s very human tendency to use a substitute more than once rather than search for a new one among the hundreds at his disposal.
In book cipher, any agreed book, or other written or printed document, will serve as a key-volume, so long as it is one that is sure to be at hand when wanted. Words, or letters, can then be represented by a series of numbers usually indicating: page, (column) , line, serial position. One letter or one word may thus have a substitute such as 20-1-4-32. ”

“ Any one of the multiple-alphabet ciphers may change keys at each new group instead of with each consecutive letter. As a rule, this kind of encipherment is never found except in connection with very simple ciphers, and the intact plaintext groups, each one standing on its own key-line, are readily discovered by the decryptor who takes the precaution of cutting out a segment from his cryptogram and “running down the alphabet,” first treating the original letters and then, if necessary, their complements. ”

“ Decryptment, too, can parallel that of the Vigenère: The period of a cryptogram can be found through repeated sequences, or, in their absence, through repeated single numbers, and individual frequency counts can be taken on the several alphabets of the period. If the arrangement of letters in the checkerboard is that of the figure, or any other strictly alphabetical one to which the order of the numbers can be adjusted, these frequency counts will all follow the graph of the normal alphabet, with allowance made for the missing letter. ”

“ The term cipher implies a method, or system, of secret writing which, generally speaking, is unlimited in scope; it should be possible, using any one given cipher, to transform any plaintext whatever, regardless of its length and the language in which it is written, into a cryptogram, or single enciphered message. ”

“ Experience shows that the most cunningly constructed cryptograph, if suspected, can and will be unriddled.
An unusually secure mode of secret intercommunication might be thus devised. Let the parties each furnish themselves with a copy of the same edition of a book--the rarer the edition the better--as also the rarer the book. In the cryptograph, numbers are used altogether, and these numbers refer to the locality of letters in the volume. For example--a cipher is received commencing, 121-6-8. ”

“ Thus the taking out of columns from the second block will, at times, select one each from two or
more different progressions of 6, and the new columns, throughout some portion of their length, will differ from one another by exactly 6, the original key-length.
We have seen, then, the general case in which the “enemy” decryptor, having several cryptograms of the same length, enciphered with the same key, is able to use a purely mechanical method in order to restore the plaintext, and afterward, by observing traces of a known cipher, to extract their key. ”

“ On what principle had these letters been arranged? He who held the paper was alone able to tell. With such cipher language it is as with the locks of some of our iron safes—in either case the protection is the same. The combinations which they lead to can be counted by millions, and no calculator’s life would suffice to express them. Some particular “word” has to be known before the lock of the safe will act, and some “cipher” is necessary before that cryptogram can be read.
He who had just reperused the document was but a simple “captain of the woods.” ”

“ The subject which we are about to study is the analysis and solution of cipher, though not including code, which is a very special form of cipher demanding something more than elementary knowledge; nor shall we enter at all into the subject of invisible inks, certainly a most important aspect of secret writing, but belonging to the province of chemistry rather than to that of cryptanalysis. Cipher machines, also, are not within our present scope. ”

“ Naturally, there are times when the matching of the columns, for one reason or another, proves troublesome. We are thrown off by errors, by the presence of nulls, initials, abbreviations, etc., or by the encipherer’s use of cover-up devices, such as the writing of YH instead of TH. Or we find that the handling of many paper strips, caused by message length, is awkward and confusing. But if, in the eyes of the decryptor, there is any good reason for finding out the contents of such messages, he can always succeed, even with only two letters per column. ”

“ So far, nothing has been said about helping ourselves to the serial numbers of [page 59] the columns, which, during the rearrangement of letters, are automatically forming in a certain sequence across the top of the set-up. Regardless of the cipher, it can do no harm to examine these, and find out what information, if any, they are able to give. In some cases, they will provide us with both the system and its key, enabling us to throw away the strips and start deciphering. ”

“ CRYPTOGRAPHY (from Gr. κρύπτος, hidden, and γράφειν, to write) , or writing in cipher, called also steganography (from Gr. στεγάνη, a covering) , the art of writing in such a way as to be incomprehensible except to those who possess the key to the system employed. The unravelling of the writing is called deciphering. Cryptography having become a distinct art, Bacon (Lord Verulam) classed it (under the name ciphers) as a part of grammar. Secret modes of communication have been in use from the earliest times. ”

“ Usually time is saved by taking cryptogram pairs just as they come and filling in as many letters as possible; in this way, patterns are sometimes brought out, and thus we come back to step 1: the identification of more pairs. With the key-square beginning to shape up, the “chart of probable position” may be used to good advantage. For instance, what about the letters H and B which were very high in the frequency list?
Once a beginning is made, the cipher is broken, though just how rapidly we may proceed with the solution depends chiefly upon the manner in which the square has been filled. ”

“ Knowing that a great many letters are going to be enciphered by B, a great many others by E, and a great many others by D, and having no wish to preserve word-divisions, we begin by writing our plaintext into three columns (or by grouping it conveniently) , and then encipher at a single writing all of those letters which are to be enciphered by any one same key-letter. That is, we apply one cipher alphabet at a time, as first explained. The modern practice will also require that the cryptogram be taken off in five-letter groups, and that the final group be made complete. ”

“ Thus, the sentence given above yields a series 1, 3, 1, 2, 1, 4, 4, 1, 4. Using a biform alphabet, these are usually considered simply as odd and even; with a triform alphabet, some disposition must be made of numbers larger than 3.
The subject is fascinating, and the literature of cryptography is rich with examples. However, we need not delve further into what, after all, is only the stepchild of a legitimate science. The matter of telegraphic transmission alone will bar these ciphers for most general purposes, or the fact that a cipher once betrayed will never serve again. ”