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40

When the world was younger, and computers weren't all glorified PCs, word sizes varied (a DEC 2020 we had around here had 36 bit words), format of binary data was a contentious issue (big endian vs little endian, and even weirder orders of bits were reasonably common). There was little consensus on character size/encoding (ASCII, EBCDIC were the main ...


24

One advantage that might be overlooked is the ability to experiment. If you're shoving bits down the tube, you're going to need to write some utility that translates EHLO into 0x18 or the like. Instead of doing that, you can simply telnet into a mail server, send EHLO and be on your way. Nothing is preventing you in this day and age from writing code in ...


13

The following diagram, from a blog post I wrote, is a visual proof that it's impossible: Notice how the packet arrival times on each side stay the same, even as the one-way latencies change (and even become negative!). The first packet always reaches the server at 1.5s on the server's clock, the second always reaches the client at 2s on the client's clock, ...


10

It's not that many internet protocols are text based. In fact, if I were to guess I'd say that text based protocols are in the minority. For almost every text based protocol you see on the internet there are at least two binary protocols that people have invented to send the same or similar data. But it's true that the majority of internet traffic use text ...


9

In the crypto community, this task is known as delegated computation, or verifiable delegation. You wish to let the server (the "cloud") to do the work for you, but you also want the cloud to give you some proof that it actually performed the computation (and didn't just output a random output, and ran away with your money). A pointer, off the top of my ...


5

This protocol seems to be insecure due to the fact that Bob sends $E(R_A,K)$. This can be used by Trudy to "generate" encryptions of $E(\langle R_A+1,P_T\rangle , K)$ that will later be used to complete the authentication protocol. Specifically, consider the following attack: Trudy picks random $R_1$ and runs the protocol with Bob in the following manner: ...


4

When you say "layer", you are probably thinking of the OSI model, also known as the seven-layer model. However, real TCP/IP implementations don't actually fit the OSI model very well. The OSI model was designed by a standards committee 30 or 40 years ago, based on how the committee members thought network stacks ought to be designed -- but that was before ...


3

is a protocol a pack of algorithms and programming source codes? (in both the computer and network) No. A protocol is an abstract description of how systems communicate. Source code could be an implementation of a protocol, but the protocol is not the same as its implementation. Basically, a protocol tells a programmer "the messages should be formatted like ...


3

well, you don't really explain what happens in each step, and how the authentication procedure works, but your first suggestion is at the right direction. However, the impersonator wishes to authenticate himself, so the attack should actually be $1. A \rightarrow E(B) : A, K_{AB}${$N_A$} $2. E(A) \rightarrow B : E(A), K_{AB}${$N_A$} $3. B \rightarrow E(A) : ...


3

Your question can be interpreted in three ways: Why is numerical data transmitted in textual representation, as if it had been printed with e.g. printf()? Why do the classical application layer protocols — e.g. the ftp control channel, smtp, http — traditionally all use a 7-bit ASCII character set? (7 bit ASCII can be considered "text" because ...


3

Structured binary also has limitations in expanding it. It my days of working with FidoNet and building a gateway between it and UUCP/USNET, Fidonet's message headers were a structured binary. Expanding it by even just trying to add a byte someplace means breaking everything out there that is trying to work with it. Having a text header or protocol means ...


3

INVALID means "not in the cache," so there is nothing to flush. When you mark a cache block as INVALID it means that the data and the tag are not relevant. Similarly, for your second question. The line is not in P2's cache, so it should treat the line the same way it treats any other cache miss: (if it's a snoopy coherence mechanism then it should ...


3

The term for the problem you seem most focused on is a Sybil attack whose typical solution is some form of identity. Another mitigation is a proof of work system that makes account creation expensive. The goal is to have the cost of creating multiple accounts not be worth the gains. This is more effective when one needs many Sybil accounts to really benefit....


2

(re-post of my comment as an answer) The only party that generates encryptions of messages $m$ such that $m$: contains 3 parts begins with a "2" is Alice. Each time she generates such a chipertext, the last component is $P_A$. If $E$ is a strong enough encryption (non malleable), then Trudy will not be able to generate by herself a an encryption $E(m)$ ...


2

Definitely, the window boundaries will be updated, in other words, the window will be shifted regardless of the fact remaining packets are strictly less than window size. But the main point is after shifting,window will not be fully occupied.The window in sliding window protocol is a buffer, which stores only those packets whose acknowledgement is not ...


2

I don't think it makes sense to use the binomial distribution. The point of using the Poisson distribution is that network nodes are assumed to want to transmit with an exponential distribution at some rate. This is a reasonable model for objects that randomly emit stuff – for example radioactive decays follow this distribution. Given a bunch of ...


2

Hint: The condition $x + y + xy = 0$ is equivalent to the condition $1 + x + y + xy = 1$, i.e. $(1 + x)(1 + y) = 1$, or in other words, $$ (1+x)^{-1} = 1+y. $$


2

I think you actually want secure multi-party computation, not zero-knowledge proofs. In secure multi-party computation, Alice has a secret input $a$, Bob has a secret input $b$, and we want to compute $f(a,b)$ so that both Alice and Bob learn $f(a,b)$ but neither one learns anything more about the other's secret. That maps directly to your situation. In ...


2

Besides RTS and CTS, there are a few other "optional" signals such as DTR, DCD,... These signals are mostly about checking if the other end of the cable is ready. Ready can mean that the internal buffer is not full, or related to some hardware condition, such as being powered or that the phone line is up ("DCD"=Data Carrier Detect). These signals can be ...


2

The space isn't used if there isn't data to send. If you're writing a letter, you write as much as you need and you don't insist that the last page must be full of writing. And you don't wait until you have something extra to say to fill that page, because that would delay the rest of the letter.


1

I don't understand why it can only output the input it has seen already. The reason is simple. Just too simple. Because it cannot output any input that it has not seen deterministically, where the input could take one of two (or more) values randomly. Let me use an example. Suppose you and I are two travellers (threads) travelling together. Each of us ...


1

As pointed out in the answer by gnasher, a packet is nothing more than a sequence of bits. The actual transmission depends on the underlying physical medium. In case of wireless networks, we transmit using radio signals or microwave signals or infrared signals. How do we send information via signals? We modulate the wave. We take the initial signal, ...


1

A packet is a sequence of bytes. Nothing more, nothing less. When transmitting packets, a signal is formed in such a way that boundaries between packets are easily identified, and that the bytes forming the packets can be transmitted and decoded by the receiver. Electrical signals at high frequencies must be formed in such a way that they are not damaged ...


1

If you want strong protections for the identity/anonymity of the participants, you might be interested in systems for anonymous communication, such as Tor. If you're just interested in systems where the destination's address isn't necessarily known under normal operating conditions (but it's not a critical security goal to ensure it can never be known), you ...


1

Take the last m bits of the hash. View it as a number in binary. That's how you convert the hashed value into a number. The position is a number. That should answer your questions 1 & 3. Now that you know how it works, you should be able to answer question 2 yourself. If not, go back and read the original paper (especially Section IV.B), which ...


1

RTS/CTS are signals used to control data flow when the input and output rates are different. When the rates are identical then there is no need for flow control.


1

There is a new field of homomorphic encryption that generally fits your requirements: Homomorphic encryption is a form of encryption that allows computations to be carried out on ciphertext, thus generating an encrypted result which, when decrypted, matches the result of operations performed on the plaintext. The processing entity cannot know "anything" ...


1

Simple answer: The 127.0.0.1 address is an IP layer concept, so it has to be handed to the IP layer for correct routing and so. More complex answer: The 127.0.0.1 address might be common enough in practical use that upper layers of the TCP/IP stack in your particular operating system cut corners and handle it specially. Even your application might figure ...


1

If the limitation is coming from the site, then it depends if the server allow you to resume partial downloads. If yes you can have two devices, one downloads the first part of the file, and the second one downloads the second part (telling the server it has already the first part). The IP-address is given to you by your internet provider and it is unique. ...


1

Hints: Try working out the binary representation of 245.248.136.0 (it's 32 bits) and of 245.248.128.0. Re-read what the /21 and /22 notation means and how CIDR works. What is the range of IP addresses included in 245.248.128.0/22? in 245.248.136.0/21? I think once you understand the concepts you'll find that this question is straightforward. Advice: ...


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