10
votes
2answers
2k views

How is XOR used for encryption?

I am a programmer, so when I hear XOR, I think about the bitwise operator (e.g. 0110 ^ 1110 = 1000). The mention of "XOR" comes ...
2
votes
2answers
156 views

Is Encryption without knowing the input directly possible at all?

I know the question is rather unusual, but let me clarify what I'm searching for: There is one person, lets call her $Alice$. $Alice$ has $n$ plaintexts $t_1..t_n$ and $n$ public keys $pk_1..pk_n$ of ...
3
votes
2answers
184 views

Why isn't CTR mode (counter mode) used more often?

For the CTR mode, the design is good for parallelization, yes, it seems the benchmark of the program downloaded from crypto++ proves that on an Intel I7 CPU. My question is that as most of CPU on ...
1
vote
0answers
27 views

Double-and-add/Montgomery VS blinding

I'm having a hard time understanding why people use constant-time techniques to counter time-attacks, when blinding seems as good and cheaper to implement. Why do people avoid blinding in ECC?
0
votes
1answer
46 views

Verification of Pinocchio (verifiable computation)

I am reading the Pinocchio paper. The calculated result $y$ is a part of the verification input, but it seems to me, the verification procedure does not utilize the result $y$. Can anyone can help me ...
1
vote
1answer
77 views

Beginner question about secure communication with one user using DES

I am currently learning about encryption and I was asked a question: If a customer only had a DES system how could I secure messages as DES is not secure. I was researching this and I came across a ...
0
votes
1answer
79 views

Super-simple encryption of short strings

I want to anonymise the initials of experiment participants by giving each a pseudonymic set of initials, by encrypting their true initials. Their initials are only two or three letters in length. ...
0
votes
0answers
42 views

side channel attacks against TDES (compared to AES)

We all know AES has some pretty strong side channel attacks, some where (with a couple of hundred know plain- and ciphertext combinations) a key can be derived in a matter of minutes. Others may take ...
0
votes
1answer
26 views

EC based authenticated key exchange

From my little understanding of EC based authenticated key exchange protocols that it is not possible for authenticated key exchange without signing/signature scheme, please confirm? If both client ...
2
votes
1answer
177 views

Elliptic curve cryptography G*G

I understand how ECC works for the point multiplications and stuff. All we normally do is to multiply a scalar number (lets say d as a private key) with the base point generator ...
0
votes
0answers
17 views

Solution for Protocol Downgrade Attacks [migrated]

I have a Protocol Downgrade Attacks i have seen the solution to be as TLS Fallback Signaling Cipher Suite Value (SCSV) for Preventing Protocol Downgrade Attacks Can anyone suggest how can we ...
0
votes
0answers
36 views

Protocols with deliberate errors

This question is motivated by discussion cocerning “The Two Sheriffs” puzzle, see (1) and (2). Are there any public key protocols where Alice and Bob intentionally insert errors in their messages? ...
-1
votes
1answer
81 views

Decrypting an encrypted text file

I have encrypted a text file which contains few lines of text. After performing the encryption process, the encrypted text is saved into a text file. The Cipher text for the word "Inform" is "24 102 ...
1
vote
1answer
75 views

Known plaintext attack on 3 round SIMON block cipher

I am attempting to write a program to perform a linear approximation attack on a reduced round version of the SIMON block cipher, but I am stuck on how to actually apply the linear approximation to ...
1
vote
0answers
32 views

Cache Attacks on Cloud Infrastructures

I read something about cache attacks like this: Enter KSM (Kernel SamePage Merging). KSM enables the kernel to examine two or more already running programs and compare their memory. If any memory ...
24
votes
6answers
17k views

Are there two known strings which have the same MD5 hash value?

Is there an example of two known strings which have the same MD5 hash value (representing a so-called "MD5 collision")?
8
votes
1answer
407 views

How does ECDH arrive on a shared secret?

I read a brilliant, three part article on Elliptic Curve cryptography (one, two, three). It was able to explain Elliptic Curves to me in a way that didn't require a math degree to understand. The ...
7
votes
0answers
213 views

Is it possible to break enigma code with a todays laptop

I have a 500 characters enigma encoded text. Random rollers were used (not the ones from wikipedia). I know of this flaw. I can guess some words that sould be in the text, but this probably doesn't ...
7
votes
2answers
350 views

Is SSL getting faster because it's getting less secure?

There has been some discussion about it being more practical to use SSL due to advances in hardware. From my understanding, stronger public-key encryption means that both encrypting/decrypting and ...
2
votes
1answer
55 views

what are the NTRU keysize and application in industry ?

I'm a student currently working on a research project on the NTRU cryptosystem, I've read some papers about this cryptosystem, and in those papers they are talking about keysize, is it the size of the ...
0
votes
1answer
48 views

Why rogued certificate from hash collision is harmful

I cannot understand why rogued certificate is thought harmful though It can be used to impersonate some website. The attacker can craft a rogued certificate with different identities and public key ...
0
votes
1answer
37 views

Different keys for clients but 1 key on server

Is it possible to have different keys on alot of (embedded) devices and just have 1 key on a server (to witch all these devices connect)? The main point here being when 1 device is compromised this ...
1
vote
1answer
59 views

What is SHA-256 in Conjunctive Normal Form?

What is the conjunctive normal form (CNF) representation of $\text{SHA-256}(m)=h$, where $m$ is of fixed (or bounded) size and $h$ is 256 bit?
0
votes
1answer
58 views

Is there any patent free EC point compression available? If not, should I GPL/LGPL my code?

I'm currently using the BouncyCastle implementation in uncompressed mode, and considering releasing an optimized version of EC code that uses point compression. It appears the only thing limiting me ...
0
votes
2answers
53 views

Integrity compromised - HASH modified

As we are all aware that HASHing is user to verify integrity in cryptography. I have a query about hashing. Suppose a man in the middle attacker manipulates the data and creates new HASH (by running ...
2
votes
2answers
2k views

phi(P*Q) = (P-1) * (Q-1)

I was trying to understand RSA when I encountered the Euler Function. I do understand this: $\phi(P)$, where $P$ is a prime is $P-1$. However it seems that for a number $N$ such at $N=P\cdot Q$ where ...
0
votes
2answers
48 views

Are there drawbacks to encrypting data locally before being encrypted in cloud backup (multiple encryption)?

I am planning on backing up my hard drive using a cloud backup service but have become skeptical of the industry based on incidents like these: ...
3
votes
0answers
60 views

Under what conditions did a Bletchley bombe stop?

I am trying to understand the conditions necessary for one of the Bletchley Park bombes to stop. Let me give an example. I have been experimenting with Enigma machine and bombe simulators to try to ...
1
vote
1answer
30 views

DHKE choice of private keys

In some literature it is written that the private key should be chosen random from {2,3, ..., p-1} and in some it says {2,3, ..., p-2} I guess p-1 is a weak private key, but why is that so? The ...
2
votes
1answer
333 views

AES Affine Transformation in $GF(2^4)$

in $GF(2^8)$ the AES affine transformation is defined as \begin{equation*} b( x ) = ( x^7 + x^6 + x^2 + x ) + a ( x )( x^7 + x^6 + x^5 + x^4 + 1) mod (x^8 + 1) \end{equation*} where the polynom $( x^7 ...
0
votes
0answers
53 views

Rabin cryptosystem with 1 mod 4

We have p and q which are distinct primes congruent to 1 mod 4. Then we have n = p*q. Do you know any algorith for calculating square roots for the decryption in this case? I'm asking for some ...
1
vote
1answer
64 views

Decryption of message in IBE without random oracle using bilinear pairig reg

I find the following IBE scheme from the videos posted and i don't understand the decryption algorithm, will any one please elaborate the 6th step scheme Setup($\lambda$) : $(\mathbb{G}, ...
1
vote
2answers
32 views

correct usage of keys and nonce

I've being studying up on AES, GCM, CBC, HMAC and a lot of other primitives and am somewhat ( a little bit, perhaps) familiar with them however I am still a bit weary on the use of the keys and nonce. ...
0
votes
1answer
52 views

Attribute-based encryption for cloud storage

I'm trying to understand attribute-based encryption schemes. Almost all articles describe that they are designed for cloud storage, but as I understand, almost all computing (encryption & ...
1
vote
2answers
92 views

nonce of AES-GCM in SSL

It seems that the nonce of AES-GCM in SSL has 3 parts: salt, 4 bytes, generated in handshake, not changed in whole session nonce_explicit, 8 bytes, chosen by the sender and carried in each SSL ...
0
votes
1answer
47 views

How is the MAC or HMAC secret shared with the other party for verification?

I've seen people everywhere say to use a MAC or HMAC with block ciphers. I think I understand the basics, but I'm still not sure how the HMAC secret is distributed so the other party can verify that ...
1
vote
1answer
41 views

Words in Index of coincidence using vignere

I am trying to interpret the formula for index of coincidence from here I am not understanding fi , How i can calculate fi in this context ? Is this the appearance of single word like (...
0
votes
2answers
44 views

Length of prime number used in Pedersen Commitment

I am writing a program using a Pedersen commitment scheme and all I'm missing is an appropriate length for my prime $p$. I have heard that a length of $2^{80}$ is ok, is that correct?
2
votes
1answer
78 views

Plaintext block chaining, bad idea why?

Ahead of the question, little warning. Question is not about what are the better options. Question is why it is bad idea? Ok, suppose we have plaintext $p$, which divided into blocks: ...
0
votes
0answers
73 views

Security of basic SHA256 MAC in an authenticate-then-encrypt scheme

I know the following construct is insecure if the MAC as defined below is appended to the encrypted message in an Encrypt then Authenticate (EtA) scheme. $k_1$: encryption key $k_2$: authentication ...
5
votes
1answer
575 views

Why does applying 56-bit DES twice only give 57 bits of security? [duplicate]

Given two 56-bit keys, $k_1$ and $k_2$, why does $E_{k_1}(E_{k_2}(M))$ only give 57 bits of security? So basically I'm unsure why it only gives 57 bits of security; I understand that one key will ...
1
vote
1answer
66 views

Prove there is PRG that is not necessarily one-to-one

We assume that there is at least one PRG .Now prove there is a PRG like $G:\{0,1\}^{n} \rightarrow \{0,1\}^{l(n)} $ such that it is not necessarily one-to-one.
3
votes
1answer
93 views

Is it ever unsafe to compress an EC point?

I am working with a library that outputs EC points in uncompressed form. To save space, I'm considering modifying said library to use compressed EC points. Assuming that I keep track of the sign bit ...
2
votes
1answer
59 views

Retrieve value of private key after encryption with the public key

Is there a way to find an RSA private key after it is encrypted with the corresponding public key? Does there exist an algorithm to recover the private key in this special case?
2
votes
0answers
66 views

Proving that a plaintext is the Paillier decryption of a certain ciphertext

Assume that Alice received 100 ciphertexts encrypted with additive homomorphic encryption, say Paillier, using the same public key that belongs to Bob. Alice added all of them, and wants to know the ...
11
votes
1answer
571 views

Compressing EC private keys

For reasonable security, EC private keys are typically 256-bits. Shorter EC private keys are not sufficiently secure. However, shorter symmetric keys (128-bits, for example) are comparably secure. I ...
0
votes
1answer
31 views

Using HMAC SHA256 to protect payment files in local trusted network

in a project that I am working on we have been tasked with eliminating PGP while providing sufficient security to protect payment files only within the Company's trusted network. We arrived at HMAC ...
2
votes
1answer
29 views

Is MCrypt's 8-bit OFB mode secure?

I just stumbled across a Stack Overflow post which points out that the libmcrypt library (notably used in PHP) implements a somewhat unusual set of block cipher modes: it calls the usual CFB and OFB ...
0
votes
0answers
49 views

What are the links between Cryptography and Algebraic Topology? [on hold]

I have asked "What are application of Cryptography in Algebraic Topology". But I want to know whether are there any relation between Algebraic Topology and Cryptography. Are there any application of ...
1
vote
2answers
80 views

How does SafeNet MobilePASS generate passwords? (TOTP Variant)

This question is similar to How does SafeNet MobilePASS generate passwords? The question and answer there is related to the HMAC Variant of SafeNet Mobilepass. I'm looking for details on the TOTP ...

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