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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Can you really insert the text you want in one-time pad?

The Wikipedia article "One-time pad ~ Authentication" says : For example, an attacker who knows that the message contains "meet jane and me tomorrow at three thirty pm" at a particular point can ...
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3answers
744 views

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 ...
4
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1answer
177 views

Is it safe to assume Salsa20 to be a PRP?

Often in security proofs a certain block cipher is assumed to be a pseudorandom permutation or PRP. I wonder if this goes for stream ciphers as well, and specifically for Salsa20. If limit ourselves ...
4
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1answer
185 views

hardware and software optimizations for Salsa20

I'm using the Crypto++ implementation of Salsa20 for a software project we are working on and I'd like to know if there are any SSE or software optimizations that will increase the speed of the CSPNG? ...
4
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1answer
730 views

Fast Salsa20 in java?

For Java I'm only aware of the Bouncy Castle implementation of Salsa20. However, that version is significantly slower than AES-CTR and ARC4. There are plenty of libraries in C, but are there any good ...
2
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1answer
183 views

Security considerations on “expand 32-byte k”-magic number in the Salsa20 famility of stream ciphers?

I'm currently examining the NaCl library written by Daniel J. Bernstein and I noticed that the library hard codes the sigma: ...
7
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4answers
1k views

Is it feasible to build a stream cipher from a cryptographic hash function?

A few years ago I devised a symmetric-key system that worked like so: ...
2
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1answer
813 views

How much is slower GCM AES-128 than one of the stream chipher eSTREAM?

Evaluate the speed of the algorithm GCM AES-128 and compare it whith speed of one of the stream chipher in eSTREAM. Can someone give such an assessment?
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2answers
854 views

Which stream cipher can we replace the RC4 in the SSL?

In cryptography, the Fluhrer, Mantin and Shamir attack is a particular stream cipher attack, a dedicated form of cryptanalysis for attacking the widely-used stream cipher RC4. The attack allows an ...
7
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1answer
155 views

Specification of the scream stream cipher is unclear

I am implementing in C++ the Scream stream cipher. The Scream family is composed of Scream-0, Scream-S and Scream-F. For this question, assume that I'm using Scream-S. The specifications of the ...
2
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2answers
189 views

Stream cipher malleability

Considering a stream cipher that produces a ciphertext $c$ from a message $m$ and a key $k$ is it possible to apply operations (multiplication and/or addition) directly to $c$ without knowing the key ...
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0answers
167 views

How to perform benchmark of block/stream ciphers?

I would like to perform some benchmarking of different block and stream ciphers for general data (lossless and lossy data) encryption and decryption (with focus on power consumption). To get general ...
3
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2answers
426 views

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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3answers
388 views

Can PBKDF2 be used to create an XOR cipher key to encrypt random plaintext?

I want to encrypt a truly random plaintext (a key file) based on a user password. I'll use PBKDF2-HMAC-SHA256 to generate an encryption key from the password, but I'm wondering if I even need to ...
2
votes
1answer
64 views

Should I use distinct MACs for each user, or should I use a *direction* flag when communicating?

Alice and Bob want to communicate using a stream cipher. At the beggining, they create a session key $K_s$ and exchange it via some secure channel (using some asymmetric algorithm). After every ...
2
votes
1answer
121 views

Can stream ciphers (usually) be “run backwards”?

Is it possible to reconstruct the previous output bits of a stream cipher, e.g. RC4, when only the current state is known, or is that computationally hard, or even impossible (due to ambiguous ...
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2answers
306 views

One Time Pad Question

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?
5
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1answer
309 views

Authenticated encryption mode for stream cipher?

E. g. block ciphers have GCM or OCB, that take single cryptographic primitive (block cipher) and provide both authentication and encryption. Are there similar constructs for stream ciphers, which ...
2
votes
1answer
103 views

Using UMAC with stream cypher

I understand that most stream ciphers, due to being applied with a simple XOR, are specially fragile against data tampering, and must be used with some MAC mechanism. So I am investigating the use of ...
3
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1answer
189 views

Using same AES-GCM setup for multiple packets?

Most cryptographic libraries I've encountered uses some variant of processPlaintext(...) and then doFinal() to produce the ...
6
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1answer
290 views

Are stream ciphers no longer considered by NIST?

While reading NIST SP 800-90A, "Recommendation for Random Number Generation Using Deterministic Random Bit Generators", I noted that no stream cipher was included among the various specified ...
0
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2answers
225 views

Recommended authenticated stream cipher for minimum overhead?

I'm running my TCP/IP protocol secured by encrypting each packet with AES128/CBC, bundling a SHA256 HMAC over that packet. This causes quite a bit of space overhead for small packets, so at first I ...
2
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2answers
363 views

Combining LFSRs for Stream Ciphers: Why do we need high non-linearity?

Linear Feedback Shift Registers (LFSRs) can be excellent (efficient, fast, and with good statistial properties) pseudo-random generators. Many stream ciphers are based on LFSRs and one of the possible ...
2
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2answers
249 views

encrypt message with one digest 0-9 instead of 01-26

How much will the security of one-time pad decrease if I use one digit from 0-9 instead of 1-26? for example plaintext = "blue" and ...
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4answers
294 views

Using the output of a stream cipher, how to guarantee the integrity of 4 bytes of data?

I am designing a simple and secure stream communication protocol. My idea was to build each message sent to the wire as: (message size || clear text || UHASH(message size || clear text)) $\oplus$ ...
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2answers
85 views

Voice Call Safety [closed]

When i was dealing with an assistant of my bank through mobile call, she asked me to insert my bank login code after a beep. I was wondering if this procedure is secure against a Man In the Middle ...
2
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1answer
181 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 ...
3
votes
2answers
284 views

Number of states in a LFSR

Do all $2^{\ell}$ (where $\ell$ is the bit length of the shift register) states always occur in a LFSR or can I choose my taps badly so some states are skipped and the period is shortened? If so is ...
4
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1answer
260 views

LFSR dynamic mutation

In normal LFSR, the state is a function of the initial seed, taps positions and time, nothing else. I've seen a modification of LFSR that works like this: ...
1
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1answer
105 views

Question about use of IV in this cipher

Main cipher objective : Generate a keyed CSPRN stream, that does not expose useful information about the state of the CSPRNG, and xor this with the plaintext. To prevent an attacked who could somehow ...
7
votes
2answers
276 views

Streaming API to authenticated encryption

In regards to NaCl, I asked DJB he had any intent to add a streaming API to an authenticated cipher. His response was obvious in retrospect, that one should never release a decrypted plaintext before ...
3
votes
1answer
165 views

Non-cryptographic hash function as MAC for stream ciphers

I understand that for a stream cipher to be useful, there must be a way to verify that the message was not tampered with (bits were flipped by an attacker). So, instead of using some cryptographic ...
6
votes
3answers
284 views

Word-based stream ciphers vs “regular” stream ciphers?

Could somebody explain what is the difference between "word-based" stream ciphers and the regular ones? Those last ones use pseudo-random sequences XOR'd bit by bit with the message, as far as I know. ...
9
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4answers
2k views

What is the difference between a stream cipher and a one-time-pad?

A (synchronous) stream cipher is an algorithm which maps some fixed-length key to an arbitrary-length key-stream (i.e. a sequence of bits): $C : \{0,1\}^k \to \{0,1\}^{\infty}$. This key-stream is ...
3
votes
1answer
349 views

Are there secure stream ciphers that cannot be parallelized?

Are there any stream ciphers (or a deterministic random number generators, that should work as well I guess?) that cannot be parallelized? So for example if I seed it with a specific value, and then ...
3
votes
1answer
199 views

Stream ciphers based on discrete logs

Blum Blum Shub is a stream cipher that is provably reducible to the difficulty of factoring integers. I'm wondering whether there is a similar construction for discrete logs? For example, I could ...
2
votes
2answers
440 views

Calculating cycles per byte

Cycles per byte seems to be a critical concern in designing and choosing stream ciphers. For example, from Wikipedia, RC4 has 7 cycles/byte on original Pentium chips. How is this calculated? Do they ...
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0answers
256 views

Stream Cipher : Never use stream cipher key more than once [duplicate]

Possible Duplicate: Taking advantage of one-time pad key reuse? How does one attack a two-time pad (i.e. one time pad with key reuse)? Denote C is cipher text, m is message, and PRG(k) is ...
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0answers
378 views

Why is there a strong distinction between stream and block ciphers? [duplicate]

If I don't err, in the literature a stream cipher is one in which each plaintext bit is processed individually, commonly via xor-ing with one bit of a random or pseudo-random bit stream, while a block ...
0
votes
1answer
201 views

How to plot the distribution of a ciphertext?

Is there any plot or visualizing program that can plot the distribution of a plaintext and then the distribution of the ciphertext after applying a ciphering encryption algorithm? I am interested ...
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3answers
198 views

fixing WEP by treating all messages as one long stream

in the course of introduction to cryptography on coursera professor suggested treating all messages as a long stream XORing them with the key this way we will not need to change the key and will not ...
2
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1answer
188 views

Randomized stream cipher using multivariant quadratic equations

This is an idea I had for cipher that I thought might reduce to a known hard problem. It is efficient (compared to something like BBS) in terms of time but not in terms of space. Here's the ...
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1answer
188 views

Why RC4 used constant 24bits for initial vector

Why RC4 used 24-bits constant value + 40 bits random values to generate key?
8
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2answers
448 views

Are Stream Ciphers Less Secure?

This is by no means a scientific observation, but it seems to me that stream ciphers receive a lot less attention than block ciphers. Is there any reason for this? (Is it because block ciphers are ...
4
votes
2answers
362 views

Is any decent RNG acceptable as a stream cipher?

I have a function f(x,n) that takes a 128-bit key x, and generates n bytes of pseudo-random data. I've tested the output bytes this function for various keys with the NIST RNG testing suite (NIST ...
3
votes
3answers
260 views

Is a continuous stream of encrypted data embedded in garbage more or less secure than only encrypting the data?

Consider a communication channel that needs to be secure (Encryption can not use full "volume" encryption, since future messages are not known). Would it be better to only transmit encrypted ...
4
votes
1answer
355 views

How secure is my OTP program?

I'm writing an One-Time Pad encryption program, because I got really interested in the idea of " encryption which has been proven to be impossible to crack if used correctly". I'm writing the program ...
2
votes
2answers
285 views

Is the Blum Blum Shub PRNG suitable to create initialization vectors?

Is it a good idea to use a Blum Blum Shub Generator to create my initialization Vector (IV) in AES-OFB (Output Feedback Mode)?
5
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0answers
414 views

How can I find two strings $m_1$ and $m_2$, knowing that I know $m_1 \oplus m_2$? [duplicate]

Possible Duplicate: How does one attack a two-time pad (i.e. one time pad with key reuse)? I recently started to follow the cryptography class of Dan Boneh on coursera.org and the first ...
5
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3answers
644 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 ...