2
votes
2answers
114 views

What is the impact of different modes on pseudo randomness of AES?

AES in CBC-MAC mode is proven to be good PRF . But is there any study done on other modes ? how good is ECB mode as PRF ?
4
votes
1answer
179 views

Keyed digest function with odds of collision below the birthday bound?

I wonder if it is possible to devise a function $F(K,S,R_S)\mapsto D$ where: $K$ is some key (I have freedom on $K$, it could even be generated by a trusted party); $S$ is in $\{0,1\}^s$, say ...
1
vote
0answers
147 views

Pohlig-Hellman exponentiation block cipher

Let $G$ be a group of order $n$ and let $e,d$ be integers such that $ed\equiv 1 \pmod{n}$. Then the exponentiation maps $x \mapsto x^e$ and $y \mapsto y^d$ are inverse maps on $G$. These maps give us ...
2
votes
2answers
135 views

Can anyone tell me the name of this cipher please?

Can anyone tell me the name of this cipher please? I know it's a simple substitution cipher, I just don't know the name of it. Cipher Key: help Cipher alphabet: ...
6
votes
2answers
362 views

Can the XOR of two non-collision-resistant hashes be collision resistant?

Suppose I have two hash functions, of which neither (or only one) is collision resistant, and I want to create a new hash function by taking the bitwise exclusive or (XOR) of the results of those two ...
1
vote
0answers
70 views

When do I need to renew keys for Salsa20 or HMAC?

I currently have a system which uses two keys sourced from a single key subjected to HKDF. One key is used in the Salsa20 stream ...
0
votes
0answers
113 views

So what is quantum cryptography anyway?

I am having difficulty understanding quantum cryptography concepts. I've searched the internet and watched some videos on youtube explaining the topic, but it is still hard to understand how it works. ...
3
votes
1answer
213 views

Public-key cryptosystems without poly-time quantum attacks

It's well-known that Shor's algorithm can solve integer factorization, discrete logarithm and discrete log over elliptic curves in cubic time. This implies that cryptosystems like RSA, ElGamal, and ...
8
votes
1answer
285 views

Did NIST verify “post-quantum” claims in the SHA3 proposal papers?

I have been reading Bernstein’s “Quantum attacks against Blue Midnight Wish, ECHO, Fugue, Grøstl, Hamsi, JH, Keccak, Shabal, SHAvite-3, SIMD, and Skein” paper from 2010… This document disproves ...
2
votes
1answer
55 views

are ideal hashes possible to create?

In a hash function, you map an input of arbitrary length to an output of finite length such that the relationship is one-to-one (or at least that's what you are trying to achieve). Hence, isn't it ...
0
votes
1answer
549 views

ECC key size and signature size

My understanding of ECDSA signature length is that it depends on the key size. So for instance, if a "prime256v1" is used, the signature length will be 64 because (n/8)*2 and for "secp384r1" it will ...
-1
votes
1answer
134 views

How do I cryptanalyze a password field?

In a PostgreSQL database, I can see the following fields in a table (for a specific record): User = administrator Password = "ceMv9Me6go" Now the following are true: The password length is not ...
1
vote
1answer
78 views

collision resistant summarizer for long hash values

how we can summarize SHA-256 into shorter values when we for example can't handle more than 128 bits on system? its better just use first 128bit and ignore the rest of bits or split full value and XOR ...
3
votes
1answer
233 views

File Hash of Encrypted File

Simple question. I have a source file and I have encrypted it with a certain public key. If I take this exact same source file, encrypt it with the exact same key a few hours later would the file hash ...
2
votes
3answers
480 views

How do I test my encryption? (absolute amateur)

I am a hobby programmer with a background in biology and have developed an encryption program based on DNA. I tried to make it hard to crack, but it's essentially a substitution cipher and uses the ...
2
votes
2answers
5k views

OTP from Sony BIOS password recover

From Dogbert's blog: Sony has a line of laptops ("Vaio") which compete mainly in the high value market segments. They implemented a master password bypass which is rather sane in comparison to the ...
4
votes
2answers
901 views

In RSA, why is it important choosing e so that it is coprime to φ(n)?

When choosing the public exponent e, it is stressed that $e$ must be coprime to $\phi(n)$, i.e. $\gcd(\phi(n), e) = 1$. I know that a common choice is to have $e = 3$ (which requires a good padding ...
1
vote
2answers
85 views

What is the difference between PPE and SPPE?

Can somebody explain, in simple terms, the difference between Pseudo Random Permutation Ensemble and Super Pseudo Random Permutation Ensemble?
4
votes
2answers
200 views

Do test vectors ensure a cipher is free of backdoors?

If a cipher implementation passes unit tests using test vectors from some trusted source (these for AES, for example), then can we say that it is fully conforming to the specification, and must have ...
3
votes
2answers
135 views

iterated discrete log problem

Consider the following problem: given $g_1 \ldots g_i,h_1 \ldots h_i \in G$, $\forall i$ find $x_i$ such that $g_i^{x_i}=h_i$ For $i=1$ this is the discrete log problem and is assumed to to have ...
4
votes
5answers
890 views

Software implementation of a commutative cipher?

I've got an application (detailed below) that calls for the use of a cipher that is commutative. I've been doing some googling & reading, and there are two algorithms that seem to get mentioned ...
4
votes
3answers
336 views

Is there a public key semantically secure cryptosystem for which one can prove in zero knowledge the equivalence of two plaintexts?

If Alice encrypts two messages $a$ and $b$, such that $x=E(a)$, $y=E(b)$. Can Alice prove (without revealing $a$, $b$ or the private key) that $a = b$? Obviously the proof must not be too long and it ...
6
votes
5answers
699 views

Applications of Group Ciphers

I've been reading a paper [1], and I've ran across something called a "Group Cipher", which is similar to homomorphic encryption, with an important difference. In homomorphic encryption we have an ...
3
votes
1answer
432 views

What's the main difference between Pohlig-Hellman and RSA?

Both Pohlig-Hellman and RSA perform encryption and decryption by exponentiation modulo some integer ($p$ prime for PH, $n$ composite for RSA). They both use a key $e$ as the exponent to encrypt a ...
6
votes
0answers
94 views

Has the distributed project “Number Fields @ Home” project benefited cryptography in any meaningful way?

Is there any new understanding, property, or knowledge that has come from the Number Fields @Home distributed computing project? Has any outcome advanced the study of cryptography, or altered ...
2
votes
2answers
221 views

How does this happen in RSA malleability?

I don't understand how the $E(m)$ turns into $E(mt)$. I mean, I don't know how does that transformation happen and how does the equation occur. $$E(m) \cdot t^e \bmod n = (mt)^e \bmod n = E(mt)$$ ...
6
votes
3answers
400 views

Slow one-way pseudo-random permutation?

I'm looking for a slow one-way pseudo-random permutation; or in other words a block cipher $E_K: P\in\{0,1\}^b\mapsto C\in\{0,1\}^b$ with moderate block size $b\approx 64$ bits, wide key $K$, ...
3
votes
1answer
96 views

Block Cipher Mode Amicable to Fast Key Change/Rotation Like XOR?

I'm working with documents encrypted in long term storage. When a client requests the document, the document should be delivered encrypted under a distinct key (distinct from the long term storage ...
5
votes
3answers
246 views

AES column mixing and S-Box confusion

I am trying to understand the AES encryption algorithm. I know that we process 128 bits at a time for a 128 bit key in a 4x4 octet form, but am confused by the following: How does the substitution ...
5
votes
4answers
676 views

Is it possible to create an open-source SecurID?

As far as I understand it, the hardware key-fob two-factor systems such as RSA SecurID depend on secret algorithms, and employ tamper-resistant hardware to prevent reverse engineering. Is there some ...
3
votes
2answers
630 views

Determine the Key given ciphertexts and plaintexts?

Given two sets of plaintexts and their corresponding ciphertexts, how does one determine the key $K$? The ciphertexts are: $$C_1= (P_1 \oplus K_0) + K_1$$ and $$C_2= (P_2 \oplus K_0) + K_1$$ $K = ...
3
votes
2answers
189 views

differential and linear cryptanalysis

I have been reading about differential and linear cryptanalysis. They were mainly introduced by Adi Shamir and Biham to show weakness of DES. However, many of articles state that they have been ...
6
votes
2answers
1k views

RC2, RC4, RC5 key length

While reading the Wiki page on RC4 I noticed that the key size must be in the range of 40–2,048 bits. So should I understand like this, that I can have a key that has length of, lets say 333 bits? ...
3
votes
3answers
338 views

What are the pros/cons of using symmetric crypto vs. hash in a commitment scheme?

In a commitment scheme, are there any differences on using a symmetric cipher versus using a hash? If at the "opening", I have to reveal $r$ (a random number concatenated with the messaged at the ...
3
votes
2answers
280 views

Encryption Key derivation from numeric PIN?

I want to store data encrypted within an Android application. Keeping an encryption key safe outside the app is not an option so I looked into password derived key algorithms. I found a nice example ...
3
votes
3answers
152 views

Can one use a Cryptographic Accumulator to efficiently store Lamport public keys without the need of a Merkle Tree?

One of the problems of one-time Lamport signatures is that public keys are disposed after use, so you must generate many keys and store them in a Merkle tree. The root is the "real" public key and ...
1
vote
3answers
365 views

Does it make sense to block RSA keys under 1024 bits?

A paper I found (http://eprint.iacr.org/2012/064.pdf, which was submitted to a cryptography conference about two years ago), is based on the analysis of some 7.1 million 1024-bit RSA keys published ...
2
votes
2answers
99 views

Could someone reuse client certificates?

To my understanding, if a server “cert+key” (RSA) is compromised, than the SSL/TLS network traffic can be decrypted. What about a client “cert+key” (RSA)? Could someone reuse client certificates? ...
3
votes
1answer
206 views

How is an AES Encrypted Message Decrypted with Random Padding?

One thing I was surprised to learn about AES is that random padding can be added to the message to make it a multiple of block size. What I can not wrap my head around is how this random padding can ...
2
votes
1answer
171 views

Diffie-Hellman: Does the size of the prime modulus depend on the potential size of the secret?

I'm writing my own cryptosystem that uses One Time Pad and Diffie-Hellman to generate keys for the OTP. I am using Rails on the server side and Javascript for the client side. Please don't tell me ...
2
votes
1answer
97 views

How is a PRNG used in the PGP?

I'm currently reading up on the components of PGP and I am wondering what exactly the PRNG is used for. PGP uses ANSI X9.17 and entropy from a users keystrokes to generate a temporary key. So, is ...
1
vote
0answers
87 views

Is it possible to modify SSL handshakes to enable PFS while still using RSA during the handshake?

I know we could possibly be using DH key exchange, that would enable PFS. However, what if we make modifications on our SSL 3.0 handshake such that the only cipher we use is RSA for the achieving PFS? ...
2
votes
1answer
100 views

How well does breaking multiple DH key exchanges over the same group scale?

Suppose you are running a server with the Diffie-Hellman parameters (so the group G and generator g) generated once. There are ...
4
votes
1answer
573 views

What does Maj and Ch mean in SHA-256 algorithm?

I'm guessing they're some kind of standard function but what do they do and what do the names mean? A little explaination or link me to an article would be great.
1
vote
1answer
162 views

How should I manage Diffie-Hellman parameters on a Web Server?

Is there a best practice for Diffie-Hellman parameters (p, g, and q) used on a web server? The server is using ephemeral keys, but should the parameters be rotated on a regular basis? Is it OK for ...
1
vote
0answers
67 views

Can you provide an example in relation to Hidden Field Equations Multivariate?

I'm reading about Hidden Field Equations Multivariate scheme. My lecture states that the central map is a univariate polynomial $$P(X)=\sum_{i=0}^{r-1}\sum_{j=0}^{r-1}p_{ij}x^{q^i+q^j} \in K[X]$$ ...
1
vote
0answers
120 views

Where can I find examples of ECC implemented in VHDL?

I am looking into implementing ECDSA signature and ECDH key agreement in a Xilinx FPGA. All the examples I have found of VHDL implementations skip over how to construct the low level ECC primitives ...
1
vote
1answer
90 views

Would this prevent FNV1a 32 bit hash collision?

I am considering the FNV1a 32 bit hash as part of a simple software security and authentication system. I am aware that FNV1a is NOT ideal but it may suit my needs. I am aware that FNV1a has rather ...
9
votes
3answers
232 views

How hard is to invert the function that computes the middle-bits of (x^2)?

I'm designing a function f that should be moderately hard to invert and very fast to evaluate in a modern CPU. The function will be used in a proof-of-work function. I've read that the middle-bits of ...
2
votes
1answer
189 views

Does SpongeWrap (from the Keccak team) absorb ciphertext or plaintext?

I have been reading the Cryptographic sponge functions paper, but I'm still confused. Does Keccak in authenticated encryption mode absorb ciphertext or plaintext? Edit: Are there any test vectors to ...

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