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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97 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
85 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
150 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)) $\oplus$ ...
2
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1answer
75 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 ...
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2answers
66 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 ...
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1answer
61 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 ...
2
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2answers
132 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 ...
3
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1answer
207 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:
...
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1answer
72 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 ...
2
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1answer
59 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 ...
2
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1answer
111 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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1answer
62 views
Super-symmetric Stream cipher [closed]
What I want to know is, Is there a stream cipher with two modes Mode-1 (encrypt/decrypt) and Mode-2 (decrypt/encrypt)
i.e. it should be possible to encrypt and decrypt using Mode-1 and Mode-2 ...
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2answers
178 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 ...
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1answer
73 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 ...
5
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3answers
185 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. ...
6
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4answers
920 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 ...
2
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1answer
1k views
Difference between stream cipher and block cipher
A typical stream cipher encrypts plaintext one byte at a time, although a stream cipher may be designed to operate on one bit at a time or on units larger than a byte at a time.
A block cipher ...
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1answer
180 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 ...
2
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1answer
144 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 ...
6
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2answers
299 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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2answers
191 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
63 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
99 views
Secure Pseudorandom Number Generators [closed]
Can anyone list the pseudo-random number generators used in todays stream ciphers that are considered secure or highly resistant to cryptanalysis?
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2answers
198 views
Why is there a strong distinction between stream and block ciphers?
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
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1answer
122 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
113 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 ...
1
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1answer
126 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
95 views
Why RC4 used constant 24bits for initial vector
Why RC4 used 24-bits constant value + 40 bits random values to generate key?
6
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2answers
316 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 ...
2
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2answers
183 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
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3answers
171 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 ...
1
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1answer
91 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 ...
4
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1answer
267 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 ...
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2answers
201 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)?
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0answers
380 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 ...
4
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3answers
393 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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2answers
84 views
How can I protect against the failure of a block or symmetric cipher?
Can I protect against the failure of a block or symmetric cipher by chaining different techniques together? If so what implementation details should I be aware of?
Are some combination of ciphers ...
3
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2answers
282 views
Finding the LFSR and connection polynomial for binary sequence.
I have written a C implementation of the Berlekamp-Massey algorithm to work on finite fields of size any prime. It works on most input, except for the following binary GF(2) sequence:
$0110010101101$ ...
3
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2answers
272 views
are CFB and OFB really meant for streaming?
CFB, OFB and other modes are meant for streaming and don't require padding. Are there still limitations such as the text needs to be greater than key length?
48
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10answers
3k views
Is modern encryption needlessly complicated?
RSA, DES, AES, etc. all use (relatively) complicated mathematics to encrypt some message with some key. For each of these methods, there have been several documented vulnerabilities found over the ...
2
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2answers
253 views
Simple xor cipher extension
Probably the simplest cipher is the xor cipher with a single integer. One can extend this to use more than one integer by several means. I'm wondering if there is any benefit to doing more than this:
...
9
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4answers
424 views
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, ...
3
votes
3answers
350 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 ...
3
votes
3answers
362 views
Stream cipher add instead of xor
In a stream cipher, the bytes of the plaintext are usually XORed with the keystream to produce the ciphertext. Would there be anything wrong with adding the bytes instead (with overflow), if adding ...
2
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1answer
86 views
Is the following scheme secure for different cipher
Let's say I have
two keys K1 and K2.
two messages M1 and M2 of the same length.
Cipher (E,D)
3 ciphertexts: C11, C12,C22 where Cij = E(Ki, Mj)
In situation ...
0
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3answers
260 views
Can PBKDF2 be used to create an OTP 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 both ...
3
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4answers
496 views
Stretching a random seed to maximize entropy
I'm using a random number generator that requires me to pass it a big (several kilobytes) pool of random data for initialization.
I've gathered entropy from various system metrics (free memory, ...
3
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4answers
374 views
Why isn't the alternating step generator used more often?
According to the Wikipedia entry for the Alternating Step pseudorandom number generator, there is no public cryptanalysis for this device since it was invented back in 1987 by C.G. Gunther. I have ...
12
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4answers
689 views
With sufficient randomness, is XOR an acceptable mechanism for encrypting?
I have heard criticism of various cryptosystems saying that "at their heart, they were just XOR."
Is this just ignorance, or is there something inherently wrong with XOR based ciphers?
4
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3answers
543 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:
...
