A stream cipher is an encryption algorithm which encrypts arbitrary length plain text, using a (fixed length) key. Some stream ciphers generate a key stream from only the key, which is then XOR-combined with the plain text, others feed back plain text or cryptotext into the algorithm to create the ...

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Classification of a stream cipher

How would one classify a stream cipher that is neither synchronous, nor self synchronizing? I would have thought asynchronous, but from all the sources I can find, asynchronous is synonymous with ...
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155 views

Advantages of making streamcipher stream depend on plaintext?

Most descriptions that explain how streamciphers work (like the one on Wikipedia), tend to describe a model that boils down to a simple “$ciphertext = plaintext \oplus stream$”, where the stream is ...
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Can the backdoor in Dual_EC_DRBG be used to create a public key stream cipher?

Dual_EC_DRBG has the property that if $Q = e\cdot P$, someone who knows $e$ can break the PRNG. This seems to lead to a public-key stream cipher: Alice chooses a random $P, e$, where $P$ is a ...
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1answer
132 views

How to clock a linear feedback shift register?

I have some trouble understanding what happens when a LFSR is clocked. I have tried many examples but I do not get the correct result. Can anyone point out my errors? I have the following polynomial: ...
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1answer
199 views

Any stream cipher with avalanche effect?

As far as I know, all stream ciphers work by generating a stream of pseudo random bytes, and XOR it with the plain text to get the cipher text. It has the property that one bit change in the cipher ...
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Are there known practical attacks on RC4-dropN? [duplicate]

RC4 is known to leak information about the first few bytes of the ciphertext due to keystream biases. However, are there known attacks on RC4-drop[N] where N is large enough, that leak information ...
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1answer
114 views

chacha20-poly1305 padding and length encoding

The AEAD construction for chacha20-poly1305 described in the IETF proposal encodes message lengths into the text that is to be hashed. The newer proposal goes further and pads associated data and ...
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33 views

emulation of a one-time-pad based on multiple keys of running cipher

a one-time-pad cipher is one that uses a long "truly" random key that is as long as the plain text message. the key must be only used once. the key must not be derived from pseudo random number ...
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1answer
89 views

Can somebody help me understand RC4 Spritz? (Three Questions)

So ever since I first took a stab at understanding stream Ciphers, not one stood out more than RC4, because it's so fantastically simple. As most people reading this will know, with its fantastic ...
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2answers
2k views

AES GCM vs other encryption modes in embedded environment for network traffic

I'm doing a lot of research since I'm doing an internship for a company where I need to upgrade their security level. Their own protocol needs a cryptographic upgrade and I'm leaning towards AES since ...
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2answers
85 views

Do we have anyway of knowing if avoiding self-permutation in RC4 makes it any stronger?

OK, so lots of questions get asked about RC4 but I want to make mine specific and hopefully answerable. RC4 Design as I'm sure anyone reading this knows, uses self permutation in stage 1 of the KSA. ...
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3answers
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Theoretical pi-based stream cipher

Let's pretend that all digits of pi are known and arbitrarily long sequences of digits are trivial to get. Further, some mathematician proves that there are no patterns in pi. We could create a stream ...
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106 views

Hash functions vs Stream Ciphers in terms of Speed

We know that it's possible to create a hash using a stream cipher (for instance, RC4 or AES in Counter Mode). As stated here: "A Pseudo Random Generator (PRG) and a hash function are both Pseudo ...
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1answer
583 views

Why do stream ciphers use a nonce?

My question maybe will be stupid, but my problem is that I do not understand why stream ciphers need a key and also a nonce. As far as I understand, the keystream is generated with the nonce. The same ...
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83 views

Brute force attack multiple stream cipher

Assume that a scheme used to secure a specific system $Π=(Gen,Enc,Dec)$ which is thought have indistinguishable multiple encryption in the presence of an eavesdropper. For any adversary $A$ that can ...
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How to use a stream cipher to sign a message?

Are there known constructions which allow to sign a message M (let's say it will be sent as clear text) using a stream cipher C and a symmetric secret key K? So, we have M, C, K and we want to send ...
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3answers
688 views

Brute-force attacking One Time Pads feasible?

I have a ciphertext encoded with One Time Pad. I do not know the key. How can I find the possible keys which when decoded, will result in a meaningful plain text?
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1answer
87 views

Is it interesting to design stream ciphers parametrized by a CSPRNG?

Would it be interesting to have new stream ciphers whose design is parametrized by a CSPRNG? I.e. to instantiate the stream cipher, you just have to select and plug in any CSPRNG of your choice.
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1answer
685 views

Trivium example

I started learning cryptography from Understanding Cryptography book of Christof Paar and Jan Pelzl. Here is the problem I have solved but I want to be sure that it is correct. Assume the ...
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27 views

References for combining LFSRs with different lengths and taps?

I started learning streams ciphers with the use of LFSRs. Therefore, I tried to simulate what I am learning in a C sourcecode, which combines three registers and ...
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3answers
787 views

random access stream cipher

Some time ago I was working in a pet project for a type of database engine. And I thought about securing the data in disk with encryption.. and since the main code was already developed.. I had a few ...
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2answers
110 views

Why are there so many stream ciphers out there and even ongoing research?

What make them better than OTP using a CSPRNG initialized with a secret key?
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1answer
534 views

Nonce role on stream ciphers

Modern stream ciphers usually predicts the usage of a nonce (also termed as IV) in the cryptosystem. The cost of initializing the cipher with the nonce varies from algorithm to algorithm (for ...
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1answer
661 views

What are the methods to construct a primitive binary nonlinear feedback shift register (NLFSR)?

Given a binary shift register of $n$ bits, a primitive binary nonlinear feedback shift register will generate a sequence with a period of $2^n - 1$. While I am unable to find a paper which directly ...
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1answer
92 views

Stream Ciphers and cycling questions

For all PRNGs (including CSPRNGs) lets say there is a sequence x, y, z, then when the PRNG cycles back to x, then the sequence following it will be exactly the same as before. Is this true for all ...
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1answer
44 views

Is this distributed OTP scheme secure?

This is for a distributed system: we don't want to have to maintain synchronization of random streams neither enforce uniqueness of pads because this would require some synchronization. Alice and Bob ...
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1answer
44 views

What is the significance of the Period of a Steam Cipher [duplicate]

If we only know the period of a Stream Cipher, let's say 150-200 bit in length, how can we use this information to attack a stream cipher? Taking a look at this link, What is the period of a cipher? ...
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What do we need to know in terms of plaintext/ciphertext, and how can we decrypt all ciphertext? [duplicate]

Let's say we have a cipher stream that we know has a period of 150-200bit in length. We don't know anything else about the stream cipher. If we wanted to decrypt all cipher text, what else do we ...
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2answers
277 views

Combining a keystream generator with a block cipher

I understand that: A stream cipher's security is diluted if the same key is used more than once. This is fixed by using an additional initialization vector in the keystream's computation. A block ...
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38 views

Symmetric stream cipher, is it known?

I am thinking on a simple symmetric stream cipher. My first idea is the following: The key is a set of array of random bytes ($\underline{k}_1$ ... $\underline{k}_n$), whose length is $l_1$, $l_2$, ...
4
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1answer
582 views

True Random Number Generator by milliseconds per keystroke (TRNG-Kms)

The simplest way to generate truly random numbers for OTP keys is to measure the time in milliseconds between each keystroke on a keyboard. The randomness depends on the user typing in various speeds. ...
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2answers
71 views

How to propagate error in variable-sized message?

I want to design a scheme to encrypt a variable-length message with a secret key, to provide confidentiality. The message is a short human-readable text string with byte granularity, let's say under ...
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2answers
177 views

Are all stream-ciphers IND-CPA?

A stream cipher usually generates a stream of pseudo-random bits which get XORed with the plaintext to form the ciphertext. The stream is generated using a given IV / nonce and a secret key. CTR-mode ...
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What is the PRG period of stream ciphers such as RC4 or Salsa20?

I am confused about how long a stream cipher can be used before you should change the key. To be concrete, let me use the stream cipher based on RC4 as an example. Let's say I want to encrypt a very ...
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3answers
854 views

CBC - a canonical mode, even though there are streaming modes

Why is CBC considered the canonical mode when there are streaming modes available such as CFB and OFB? One thing that I can think of is that in CBC you can easliy do range-based decryption. All you ...
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4answers
534 views

Is there a way to generate sound one-time pads out of public information?

Is there a way to 'mangle' a public data-source (for example, the current date in YYYYMMDD or the top New York Times headline) to form a one-time pad that will sufficiently hide the pad's source? ...
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When do I need to renew keys for Salsa20 or HMAC?

I currently have a system which uses two keys sourced from a single key subjected to HKDF. One key is used in the Salsa20 stream ...
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2answers
176 views

Question about the key in RC4

I am planning to develop a more secure version of the RC4 algorithm. Since I´m not an encryption expert, I´ld like you to help me find answers to the following questions: Does the value of the key ...
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2answers
399 views

Determine LFSR phase quickly?

I know it's possible with work backwards from the output bits of an LFSR to determine its feedback polynomial in a O(n) fashion. I'm also curious if, given an LFSR state and polynomial, is it ...
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1answer
135 views

Why must the sender and receiver be synchronised in synchronous stream ciphers?

I would like to know why the sender and receiver must be synchronized in synchronous stream ciphers as said in synchronous stream cipher. Why is there no synchronization between the sender and ...
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1answer
113 views

Block Cipher Modes

I have a question here asking the following: Why do block ciphers need the use of blocking modes? To encrypt messages larger than the size of the block. To avoid having the same block ...
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1answer
457 views

Dan Boneh's Cryptography lecture - problem with 802.11b

I am going through Dan Boneh's Cyprography lectures on Coursera. In Lecture 6 https://class.coursera.org/crypto-010/lecture/6 At 7:30 minutes, he discusses the problems with 802.11b design. I ...
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1answer
148 views

what are the most common stream ciphers algorithms? [closed]

say that we have an unknown stream cipher which output bytes and which have more than 10 years of existence. What can be the most probable algorithms if we consider the most 'populars' stream cipher ...
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2answers
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Distinguishing attack on stream cipher created from a block cipher in counter mode

A block cipher in counter mode creates a key stream by: $$z_i = E_K(IV || i)$$ Where $IV$ is some chosen initialisation vector (with some length $l$ less that $n$ bits) and $i$ is the binary ...
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122 views

Is it practical to use a stream cipher in a block cipher mode?

My idea is to use a stream cipher encrypting 16 bytes at a time as a primative block cipher in a mode of operation such as CBC mode. Is this practical or useful in any way?
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2answers
333 views

What does a stream cipher provide that cannot be obtained with AES CTR mode operation?

I can precompute the key stream for the CTR mode operation and the encryption at that point is similar to a stream cipher. So why are there stream ciphers still used and proposed after RC4? Recently ...
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Can you make a hash out of a stream cipher?

A comment on another question made me wonder about something: Assume you're on a rather constrained platform — say, a low-end embedded device — with no built-in crypto capabilities, ...
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XOR = Best encryption? [duplicate]

If you have a TRULY random key (in binary) and you have a text (in binary) that you want to encrypt. Can you simple XOR the key and the text? Is that secure? How secure?
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Decypting a Stream Cipher

I am trying to decrypt a stream cipher. I know what the first word of the message is when decrypted but I am unsure how to decrpyt the rest of the message. I know what the first word is because I ...
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1answer
178 views

Encryption of plain text using stream cipher algorithm

We know that in stream cipher algorithms plain text and generated key are Xored byte by byte. Generated key depends on how much plain text there is and on that basis key will generate and plain text ...