1
vote
1answer
43 views

Use of orthogonal vectors in lattice-based cryptography

In lattice-based cryptography, given the basis of the lattice we compute the orthogonal vectors using Gram-Schmidt Orthogonalization process. What is the use of orthogonal vectors in lattices?
0
votes
0answers
51 views

Importance of timing attack resistance with AES

I've implemented AES in my library with several variations: a straight C version, a version using x86 SSSE3, and a version using x86 AES-NI. The SSSE3 and AES-NI implementations are constant-time, ...
0
votes
1answer
87 views

Can anyone breifly explain the 'theta step' of compression box in SHA3?

Can you tell me the 'theta' step of compression box. D[X] = C[X-1] ^ ROT(C[X+1, 1]) In this step all the indices should be taken modulo 5. ...
0
votes
1answer
32 views

One Step Decryption For Multiple Chained Encryptions

If we have a encrypting function f(x, y) (x for input, y for key) and let's say we composite this function n times inside itself with the same y (like f(f(f(x, y), y), y)) and set the output to be z. ...
0
votes
0answers
17 views

Length Extension Attack on SHA1 [duplicate]

I am trying to understand how to perform a length extension attack on a SHA1 hash function that is used as a MAC (where the key is prepended to the hash output). If I am given the message, ...
3
votes
2answers
238 views

Why are recomended RSA key lengths so high? [duplicate]

I was checking for authoritative sources to back up my recommendation of a minimum RSA key length of 1024 and was shocked to find that NIST 800-56Br1 and FIPS 186-4 both recommend at least 2048 bits ...
3
votes
1answer
81 views

How to encrypt a symmetric key with a shared secret?

I am reading this article (pdf) on the Diffie–Hellman key exchange. It states the following: At this point, the Diffie-Hellman operation could be considered complete. The shared secret is, after ...
1
vote
0answers
27 views

Is it possible to encrypt a message with two different keys (or maybe a public key) such that ciphertext will be decrypted with either of the keys? [duplicate]

I have an app that I store sensitive user data which requires user to set a password to login the app and I use this password as key to encrypt the data. Now, I want to add an option to login the app ...
1
vote
0answers
36 views

Why was AES limited by NIST to a 128-bit block size, although Rijndael could support more? [duplicate]

Rijndael could support block sizes up to 256 bits; this seems to be useful in AEAD. Wht did NIST restrict AES to a 128-bit block size?
1
vote
0answers
44 views

Is this a better GCM?

Using the keystream from the block cipher for both parts of the GMAC key (initialization and encrypting the auth tag) seems to produce a better mode of operation than GCM, as successful forgeries and ...
3
votes
1answer
82 views

Question about HMAC with SHA1

I would like to make sure I understood HMAC. Wikipedia declares it like: $$\operatorname{HMAC}(K,m)=H((K\oplus\text{opad})||H((K\oplus\text{ipad})||m))$$ If I want to use HMAC-SHA1, am I correct to ...
0
votes
0answers
49 views

How to measure performance for ABE Schemes

I have these 3 Schemes: 1) J. Bethencourt, A. Sahai, and B. Waters, "Ciphertext-policy attribute-based encryption" 2) F. Guo, Y. Mu, W. Susilo, D. Wong, and V. Varadharajan, "Cp-abe with constant-...
4
votes
2answers
149 views

What's the issue with Apple's backdoor?

I was reading Apple's public letter here regarding the "backdoor" that they have been asked to create. I'm very unclear exactly what the issue is. There was no backdoor in the encryption algorithm ...
2
votes
1answer
69 views

Understanding Diffie-Hellman - Choosing a bad g

I am taking a class on Cryptology, and I'm having a hard time understanding the potential pitfalls of Diffie-Hellman. Specifically, the professor gave the following problem: Alice and Bob want to ...
0
votes
0answers
37 views

To understand Feistel permutations in md5

Recently I am trying to understand the md5 algorithm.In this algorithm 4 Feistel permutations FF,GG,HH and KK are used.I have faced a problem to understand the FF. The FF is defined as $FF(A,B,C,D|m_j,...
1
vote
1answer
68 views

Is there an additive homomorphic encryption that supports exponentation

For example say we have two numbers a and b. Now is there any partial homomorphic encryption scheme that allows to compute (a-b)^2 over the ciphertexts of a and b without round trips.
64
votes
8answers
6k views

Layman's explanation of encryption backdoors

Some times I read about "backdoors" in encryption algorithms in the media. I'd like to understand what such a backdoor actually consist of. Is it: a) a hidden weakness in the math formulas that ...
0
votes
1answer
38 views

Is there any place where I can find test vectors for point addition and doubling of ECC?

I want to extensively test my implementation of point addition and doubling. I have only one test vector with me. I need more values to test. In the web, I could find test vectors only for key pair ...
2
votes
1answer
48 views

finding the basis of a kernel in a lattice

Given a parity check matrix $A$ we define the $q$-ary lattice $$\Lambda(A) = \{x \in \mathbb Z^m\;:\;Ax\equiv0\pmod q\}$$ How to find the basis of the lattice and how to find its hermite normal form?
2
votes
0answers
25 views

Are there unreachable MD5 hashes? [duplicate]

Are there any known MD5 hashes that can´t occure, no matter what (finite) input is taken? Thanks
3
votes
3answers
128 views

Is an android encrypted SDcard readable/decryptable easily by a desktop machine?

If I encrypt my SDCard on my android phone using the built-in encryption software, and my phone dies for whatever reason, would I be able to easily by just using the pin/password to access that data ...
11
votes
2answers
289 views

Are there any real protocols secure in the random oracle model that have been broken in practice?

Has any protocol ever been proven secure in the random oracle model and then broken in practice, despite the use of a good hash function in the actual implementation?
1
vote
2answers
32 views

Unclear about the importance of Initialization Vectors

I was reading about Ruby ciphers and found this: Although the key is generally a random value, too, it is a bad choice as an IV. There are elaborate ways how an attacker can take advantage of ...
3
votes
1answer
61 views

Block cipher mode of operation with beyond-birthday-bound security

I am looking for block cipher modes of operation that are secure even when the number of blocks encrypted exceeds the birthday bound.
2
votes
1answer
37 views

I am trying to implement TLS v1.1 {3,1} but get alert 70 on hellomessage to goolge

I am trying to implement TLS on top of the winsock api's from windows. I am using port 443 and have created a socket. I have sent this message in decimal. ...
0
votes
1answer
50 views

How to encode a message to MD5?

I have faced a problem to understand MD5 algorithm.My question is weather the original input message is converted to binary value in MD5 before using the input message as parameter in four Feistel ...
2
votes
0answers
35 views

Can a secure MAC break if the adversary is given oracle access to Verify?

In the Mac-forge experiment, the adversary is given access to a tag-generation oracle, which generates a tag for each message given by the adversary. The adversary's task is to generate a valid tag on ...
1
vote
1answer
88 views

Finding collisions in SHA1

I am trying to find two collisions in SHA1 for the 50 least significant bits. I was wondering if there was a way to efficiently do this without having to brute force all of the possible hash outputs? ...
3
votes
0answers
21 views

Would using a symmetric list of subkeys in a Feistel cipher make our messages vulnerable to oracle attacks?

Suppose I have a Feistel cipher structure that has $16$ rounds. I come up with $8$ subkeys $k_1,k_2,...,k_8$ to be used for the first $8$ rounds and then assign the rest of the keys so that $k_9=k_8,...
1
vote
1answer
35 views

How to go about encrypting a digital exam?

I'm building a Digital Examination system and I'm having problems understanding some concepts in cryptography. I want use to Asymetric Cryptography and my questions are Do I encrypt the entire file?...
3
votes
1answer
102 views

Question on 3DES keys

The official NIST publication I saw says for federal applications 3DES with three keys should be used. I have such questions: what does it mean federal? Does it mean for industrial applications that ...
1
vote
1answer
37 views

Secure way to hash a lookup value

I want to securely store a database table that consists of an account ID and a few columns of sensitive data. The data only has value if it can be associated with the account ID. My thinking is to ...
0
votes
2answers
59 views

How to authenticate two devices with CA?

i am trying to figure out a man-in-the-middle safe authentication scheme for some devices. I understand that this could be achieved via CA's. But what is unclear to me is how can the authenticity of ...
1
vote
1answer
140 views

How vulnerable is the one-time-pad (OTP) encryption, if the OTP is used twice, with a random substitution scheme

So I was wondering, I read up about OTP encrption and can see how using an OTP encryption is in itself unbreakable. However, I looked at how OTP is broken if the OTP-key is used on more than one ...
4
votes
3answers
317 views

Homomorphism and Zero Knowledge in FIPS 140-2 compliant systems

I am analyzing a system that needs to be at least level 3 FIPS 140-2 compliant. The system may leverage from homomorphic and Zero Knowledge constructs, but, as far as I can see, the algorithms ...
1
vote
1answer
96 views

Exponent operation over element of G

I found a definition of an exponent operation over the element of $\mathbb{G}$ in this paper (page 4): $$ (g^a)^{\% b} = g ^{a \text{ mod } b}$$ I couldn't understand the rest of the paper (Decrypt ...
0
votes
1answer
30 views

Inverse in ElGamal signature

I am learning about ElGamal signature verification. During the signature generation one has to choose a k such that ...
1
vote
1answer
449 views

Is a 4DES or 5DES system possible?

We know that 3DES is created with $E_{K_3}(D_{K_2}(E_{K_1}(m)))$ to extend DES's key length. Is it possible to extend it further by repeating this pattern? Perhaps using $E_{K_5}(D_{K_4}(E_{K_3}(D_{...
0
votes
1answer
67 views

Scalar multiplication with projective coordinates

I'm implementing point addition, doubling and scalar multiplication using projective coordinates. I took reference from this link https://www.nsa.gov/ia/_files/nist-routines.pdf I have implemented ...
5
votes
0answers
133 views

Is F5 still a viable steganography algorithm? [closed]

I am currently developing a steganography application and have been studying the F5 algorithm by Westfeld. I keep on seeing from various literature and open source projects (e.g. from GitHub) that it ...
1
vote
0answers
42 views

Can an attacker recover the key if a Poly1305 collision is known?

Suppose that messages $m_1$ and $m_2 \neq m_1$, both known to the attacker, are both MAC'd through Poly1305 with the same key. By chance, these two messages hash to the same value. The attacker ...
0
votes
2answers
48 views

digital signature on image and text

i am trying to implement an android app that should "sign" an image, M and a string, S using a private key, K-1 and send the result to a server. for instance the app should be doing {M,S}K-1. the ...
0
votes
1answer
67 views

Are any public key algos commutative?

Are there any public key encryption algorithms that allows for arbitrary ordering of crypto operations (commutative). That is, given a plaintext "message1", the following operations work to doubly ...
2
votes
3answers
164 views

How to disguise ciphertext

If I want to have a secret conversation, then I can encrypt it (with OTR etc). However, since big brother watches all communication, sending encrypted data will likely raise flags. Does anyone know of ...
3
votes
0answers
32 views

Access structure in Attributes Based Encryption [duplicate]

I thought that access structure and access tree are equivalent but I've read in a paper (page 3) that there are at least three types of access structures : AND gates Access tree LSSS generating ...
0
votes
1answer
31 views

IPSec recomendations about rekeying

IPSec like strongSwan can be configured to do rekeying after time or bytes transferred or packets transmitted. Is there any recommendations to set those settings? Maybe according to algorithms used?
1
vote
1answer
49 views

Does absence of second pre-image resistance infer absence of pre-image resistance?

Talking about hash functions, I know the hierarchy is as follows: Pre-image resistance Second pre-image resistance Collision resistance Where each property implies the one before it so 2nd pre-...
4
votes
1answer
83 views

Is it possible to perform an MPC protocol to compute a product in a polynomial ring?

I hope not to be asking much, but I have N parties, each one holding a polynomial in with 0-1 coefficients and fixed degree $n-1$. I was wandering if it is possible (I mean feasible) to compute the ...
4
votes
1answer
280 views

Ciphertext notation where the ciphertext consists of two parts

I've see in several places (here or there) the notation $c = (U, V)$ or $c =\langle U, V \rangle$, where $c$ is a ciphertext (to be transmitted). But as both $U$ and $V$ are "key-like". I can't find ...
1
vote
2answers
60 views

Unkeyed, fast, one-way PRP

Are there any fast, secure, one-way, unkeyed almost-pseudorandom permutations? I am looking for something that can hide a MAC, without requiring a secret key and while being much faster than public ...

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