Questions tagged [stream-cipher]

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

Filter by
Sorted by
Tagged with
5
votes
2answers
1k views

LFSR Jump Ahead Algorithm

A related question has been asked and answered here. My question is specifically about figuring out C for very large J. I have searched the web and found many scholarly articles on "jump ahead" and ...
4
votes
1answer
440 views

I have this list of LibSodium primitives, which should I pick so that the implementations tend to be interoperable?

When I integrate lib sodium, into a c# project, and try to consume, encryption and decryption in a particular way, it works, but the confusion is about, which method to use while encryption or ...
2
votes
1answer
855 views

Cryptanalysis on Kasumi in A5/3 GSM algorithm— why is it broken in 2G and not in 3G?

I have read the Wikipedia article that states Dunkelman, Keller and Shamir managed in 2010 to mount a related-key attack in a pretty decent time (2hrs) with a Core 2 Duo. Why was Kasumi breakable in ...
1
vote
2answers
2k views

How can I create a stream cipher from a block cipher?

Assuming $k$ is the key (128 bit) and $m$ is the message (128 bit), how can I use the block cipher $blockenc(k,m)$ to make a stream cipher which can produce quintillion pseudo-random bits?
0
votes
0answers
45 views

Can Galois/counter mode be used for stream ciphers (Galois/stream mode)? [duplicate]

The authenticated encryption mode of operation Galois/counter mode has recently gained acceptance because of its high performance due to its inherent parallelism and no pipeline stalls. It requires a ...
1
vote
1answer
81 views

Looking for title of encryption machines book

I am looking for a title of book in the field of stream crypography. I vaguely remember, that I saw this book at online shop (maybe amazon) near 5-10 years ago. This book is devoted to electronic ...
1
vote
1answer
842 views

How does the zuc algorithm complete the synchronization?

I have already read the following documents: Specification of the 3GPP Confidentiality and Integrity Algorithms 128-EEA3 & 128-EIA3. Document 1: 128-EEA3 and 128-EIA3 Specification ...
1
vote
1answer
133 views

In what mode does Signal applies cryptography over voice and data?

I have read all of the technical documentations provided via signal and so far I have figured out that signal intitializes a common key via X3DH key agreement and manages the keys via double rachet ...
7
votes
2answers
154 views

Why is Vigenère Autokey self-synchronizing?

According to the Wikipedia, and to several of our school study materials, Vigenère autokey ciphers are considered to be self-synchronizing stream ciphers. If I understand it correctly, the main idea ...
2
votes
0answers
24 views

What happens in the MonkeyWrap-Algorithm of KetjeV2 if the input is a single block?

I am currently implementing KetjeV2 in VHDL. I have a question concerning the MonkeyWrap-Algorithm that is used in KetjeV2. The function $wrap(A, B, l)$ is supposed to work as shown below, where $A$ ...
3
votes
1answer
291 views

Message length limit induced by block counter size

Wikipedia reports the following information about the ChaCha20 algorithm: An implementation reference for ChaCha20 has been published in RFC 7539. The IETF's implementation modified Bernstein's ...
1
vote
0answers
81 views

What is the attack complexity if two stream ciphers are connected in cascade?

What is the attack complexity when Grain-128 and Trivium are cascaded? Is it 2^(256 + 128) since internal state of Grain is 256 bits and assuming that IV is unknown before encryption?
11
votes
3answers
610 views

Using weak hash functions to construct a stream cipher

I am in the awkward position of developing a secure encryption scheme that provides data-at-rest security for a very limited embedded system. The system is only guaranteed to have 4 MiB of memory (...
4
votes
2answers
809 views

What Cipher Suite in this list is the worst to use

I have a list of cipher suites I captured using Wireshark. Which one of these cipher suites would possibly be the worst to use. Here is the list. In my opinion, I choose the: ...
1
vote
1answer
2k views

What is the advantage of CFB over OFB?

I was wondering if CFB can be better than OFB in any ways. I would like to know in what cases one would use CFB over OFB.
1
vote
0answers
30 views

Would it possible to decode an intelligible but alien message? [duplicate]

I've been reading some sci-fi and there is a frequent mention of decoding alien signals. From what i read historically in ww2 for decoding enemy message the allies would transmit fake information ...
0
votes
1answer
2k views

Decryption of a file encrypted by pseudo-random number generator (The Linear Congruence rand()

How to decrypt this file: https://drive.google.com/open?id=1gZCujDYmEL-FZ5o_xBUS-Ng5979HSsZ7 Given that the only information available about it are: It has been created ‎on 21/3/‎2018, ‏‎9:05:15 AM ...
0
votes
3answers
683 views

Why don't block ciphers consist of a simple XOR operation with key like Stream ciphers?

If the construction of stream ciphers is already secure why does the construction of block cipher involve pseudo permutations and complex operations that makes block ciphers less faster? Is a ...
4
votes
0answers
185 views

Safely using ciphers that take small key sizes

Is it feasible to use triple encryption for block ciphers with the maximum keysize being the only significant security issue? I mean $C = E_{k_1}(E_{k_2}(E_{k_3}(P)))$ and $P = D_{k_1}(D_{k_2}(D_{k_3}(...
4
votes
1answer
107 views

Difference between one-level and two-level E0 encryption

I am trying to understand the practical security implications of the way E0 is used in Bluetooth 2.1 devices. In reading up on the subject, I am seeing that encrypting a large amount of data with E0 ...
0
votes
1answer
113 views

WEP - Vulnerable IV

When performing a FMS attack, why does the attacker have to look for a specific IV, namely, in the form of (A+3, N-1, X)? Why can't he just use any IV? This might be a naive question but I really can'...
0
votes
1answer
271 views

Finding non-zero coefficients in 8 bit polynomial LFSR

I have a following crypto problem and I have been struggling with for some time An 8-bit linear feedback shift register with connection polynomial C(X) = 1+aX +bX^2 +cX^3 +dX^4 +eX^5 + fX^6 +gX^7 +hX^...
1
vote
1answer
787 views

Finding max period of 8-bit LFSR

I am a bit stuck there and trying to figure out the approach for given problem. What is the maximim period of a pseudo-random sequence generated by the 8-bit LFSR with connection polynomial C(X) = 1+...
1
vote
1answer
2k views

How to encrypt a short plain text?

I want to encrypt a short plain text (i.e., 30bit), and the requirement is that length of cipher text is the same as the short plain text. It seems that stream encryption methods like CFB-8 ...
3
votes
2answers
2k views

What is the role of IV in Stream Cipher? Why is it needed and what is it's importance?

I ran into this problem when I read the stream ciphers and did not find a satisfactory answer. Why is an IV needed in stream ciphers, and what is the importance of using it?
0
votes
2answers
2k views

XOR and cipher stream

I am new to cryptography and I am very confused. In fact, I am so confused that I have trouble providing a suitable title for my thread... I know that a Substitution Cipher is designed to substitute ...
0
votes
1answer
102 views

Can high-entropy data be reconstructed from plaintext XORs in CTR nonce reuse?

(My interest is academic; I certainly have no intention of rolling my own crypto, especially the known-broken type!) I know that if the nonce gets reused in a CTR stream, the two cipher blocks can be ...
3
votes
1answer
250 views

Stream cipher with an additional integrity stream?

I want to use a stream cipher to encrypt a continuous bitstream. Additional to that, I want to generate an additional stream to guarantee the integrity of the ciphertext. stream a: ciphertext. ...
9
votes
2answers
493 views

Functional difference between stream cipher, XOF, seed expander, KDF, etc

This question is a request for terminology clarification. In a canonical XOF interface, the output can be extended as much as needed, but does input has to be variable-length or can be fixed-length ...
2
votes
3answers
463 views

Why this complexity defining AES-GCM counter block?

AES-GCM counter block is defined as nonce || IV || counter. Why this complexity? Knowing that it does not need to be secret and its only required property is to be ...
3
votes
4answers
1k views

Is the Vernam (One Time Pad) cipher useful? [duplicate]

By profession I’m a programmer. I don’t know a lot about how cryptographic algorithms are implemented, or even where I’d start, and I don’t know about cryptanalysis, but as I work in Blockchain ...
1
vote
2answers
1k views

How can a stream cipher encrypt one bit at a time and still be secure?

I was reading the differences between stream ciphers and block ciphers, noticing that block ciphers, encrypted blocks of 64 bits or so at a time. But, stream ciphers encrypt 1 bit at a time, and to me ...
1
vote
1answer
220 views

What is the purpose of the finite state machine in SNOW?

I do not know about SNOW 1.0, but SNOW 2.0 and SNOW 3G have a finite state machine that is used in generating the cipher's keystream output. Why use a finite state machine instead of some kind of ...
4
votes
1answer
1k views

How secure is the E0 stream cipher used in Bluetooth?

The question is about E0, the stream cipher used to secure Bluetooth communication. The impression I get is that it's more secure than A5/1. Also, why wasn't AES used instead?
6
votes
1answer
170 views

Replacing a block cipher's key schedule with a stream cipher

Take Rijndael (AES) of block size 128 and reformulate it with a tweakable number of rounds and no key schedule. Suppose we obtain: Rijndael128(r, k) where r is ...
5
votes
2answers
786 views

Why do stream ciphers like A5/1 and ZUC have “frames”?

A5/1 and (I think) ZUC, both stream ciphers used in mobile telecommunications, have "frames" where the, in addition to the key, a frame number is provided to the keystream generator which produces a ...
1
vote
1answer
469 views

What is security of stream cipher against chosen plaintext attack?

I have been looking for image encryption after compression using Ax+e, where A is a random matrix, x is plaintext and b is a bitstream generated using a stream cipher. Suppose choosing plaintext as ...
1
vote
1answer
811 views

Security of a sha-256 based stream xor cipher?

Provided that I have some data I want to cipher and a password to do it: I generate a random IV I define c = sha256(password) I generate an infinite stream where <...
1
vote
1answer
153 views

In what way is KeeLoq a block cipher?

I'm just going by this diagram of KeeLoq encryption and it resembles these diagrams of Crypto-1 and Hitag2. I'm wondering how it is a block cipher. If it is one and that diagram represents most or all ...
2
votes
0answers
129 views

Known Plaintext Attack A5/2

I am trying to understand the non-optimized known plaintext attack on A5/2 from Barkan, Bikan and Keller. I don't understand the construction of the equation system: $$S_{R4_1} * S_1 = k$$ Where $S$ ...
1
vote
2answers
571 views

Has anyone seen a stream cipher being used for FDE

So I am a newbie to this. Has anyone experimented implementing a stream cipher for full disk encryption? EDIT With the caveats that come with using a stream cipher over a block cipher of course! I ...
1
vote
1answer
134 views

Is RC4 cipher just xoring plaintext with a random sequence seeded by key?

After reading about RC4, it seems that it's nothing else than: the plaintext stream is just XOR'ed with a pseudo-random sequence that is initialized/seeded with the key Is there something else in ...
1
vote
1answer
198 views

How should k2 be produced in the RC4A stream cipher (A modification of RC4)?

RC4A is a slight modification of the simple RC4 stream cipher designed to strengthen it against a number of attacks. Here's that paper. However in the paper, the second key ...
0
votes
1answer
312 views

Does Salsa20 protect integrity?

I was reading about the differences between block ciphers and stream ciphers. One thing that hit me was that stream ciphers like RC4 tend to be susceptible to bit-flipping attacks, in which flipping a ...
1
vote
1answer
1k views

Attack on stream cipher

I am trying to decrypt a message, which was encrypted using a stream cipher and 8 bit LFSR. First two letters of plain text are given: K and ...
1
vote
1answer
106 views

how long does the cycle length have to be in stream ciphers? [duplicate]

could someone tell me how long the cycle length must be in stream ciphers, so a security exists. how to compare the cycle length to the state space? I investigate the algorithm spritz and I have the ...
1
vote
2answers
748 views

OTP stream cipher

I am new to cryptography, and there is one thing that is bothering me. I hope you can kindly help me to understand. Let's imagine an attacker harvests the plaintext as well the ciphertext from a ...
6
votes
1answer
543 views

Security of GCM if Implemented with Stream Cipher instead of Block Cipher

Can GCM be implemented with a stream cipher instead of a block cipher? If no, then what security flaw does it have? If yes, then which possibility from below two is better in terms of security? In ...
5
votes
2answers
156 views

Rueppel's example of self-clocking LFSR

Consider the following excerpt from Rueppels paper, titled When Shift Registers Clock Themselves: His example includes $C(D) = 1 + D + D^2 + D^3 + D^4 + D^5$ as a primitive connection polynomial. ...
0
votes
1answer
393 views

Robust stream cipher using AES encryption block

I am implementing a stream cipher in a microcontroller that only has an AES128 encryption block. According to this page, a block cipher based on an encryption only module can be converted into a ...

1 2 3
4
5
10