All Questions

69 views

P-Complete hashes, hashing to a larger set

Historically hashes have been from a large set (say 256 characters) to a smaller set (256 bits). Also, hash functions that are P-complete have no known parallel algorithm; they must be computed ...
180 views

Does Keccak have an eTCR mode?

On page 7 of NIST's views on SHA-3's security requirements and Evaluation of attacks, I see that, at least at this point, NIST planned on offering SHA-3 having eTCR security (defined on page 3): ...
413 views

RSA reencryption scheme

Is there such an algorithm that would allow to upgrade the encryption of a RSA-encrypted message without revealing the plaintext to the untrusted user? Basically, such an algorithm would probably be ...
60 views

Designing a secure protocol to avoid MITM?

Imagine that you are designing an online game, the framework consists of a player A, a game host H and a trusted central server S. The player A has a symmetric key KAS and id A that is known ...
193 views

In one of the hot forums of today on how to convince friends cryptography is good one of the arguments stated is the knife paradox, I was unable to find the answer on Google and my question is what is ...
37 views

Can I serve data for user without the ability to access them? Which functions for the user remain?

My Problem I want to serve sesible data for users as a webservice that is accessed by the user via the browser. Restrictions: I may not be able to technically acces the data of the user Data is ...
38 views

Is this PRG secure?

$G$ is a safe PRG in range $\{0,1\}^n\rightarrow\{0,1\}^{n+1}$. Let us define $G'(S)=G(S\oplus G(S)_{1,...,n})$, s.t. $G(S)_{1,...,n}$ is the first n bits of $G(S)$. Is $G'(S)$ a secure PRG? ...
24 views

Proving CCA security for scheme constructed from secure PRP

We have a $PRP : \{0,1\}^{3n} \rightarrow \{0,1\}^{3n}$ and encryption scheme constructed from this $PRP$. $E_k(x\|r\|0^n)$, where $r$ is randomly chosen from $\{0,1\}^n$ and $0^n$ is a block of ...
21 views

Creating an SPN cipher from ChaCha20 or Salsa20's double round function

Given that ChaCha20's building blocks have been also used to construct a hash function, can the double round function from either ChaCha20 or Salsa20 be used to construct a secure SP-network cipher? ...
38 views

CryptDB data re-encryption and onion layers

From the CryptDB paper , I understoond that the onion layers once decrypted are not re-encrypted. Only columns which are queried infrequently will be re-encrypted to higher onion layers. But if we ...
43 views

Unpredictable value rotation

I have very vey basic skills in cryptography, it's hard for me to explain clearly my problem so I will start with an example. Estimote beacons have a security function called secure UUID, once ...
62 views

Bitwise method of generating r for RSA-KEM

It seems that RSA-KEM has a very troublesome method of generating the secret $r$. It seems that the random value needs to be in the range $0 \le r \le {n - 1}$. Now most cryptographic environments ...
29 views

RC6-like key schedule with 16-bit S-boxes

I am trying to figure out an encryption algorithm whose key schedule function seems to be similar to RC6. However, it seems to be creating S-Boxes using 16-bit integers instead of 32-bit ones. I have ...
49 views

What is perfect collision-resistence in probability terms?

update: removed lots of stupidity... sorry. I didn't know I can be this stupid but I achieved it. 1. Goal Let $\mathcal{D}$ be the universal space of our plain data. Our goal is to find a function ...
18 views

CRL number generation sequence

RFC 5280 states that the CRL number should be monotonically increase. I have seen this common practice of incrementing the CRL number by 1, everytime a new CRL is generated. But can i use epoch time ...
50 views

Prove that the given scheme is CPA secure or not

Given: F is a length preserving PRP. Encryption scheme $\Pi$ for messages of n/2 bits where: $m\in\{0,1\}^{n/2}$ $k\in\{0,1\}^n$ Enc: Select a random string $r\in\{0,1\}^{n/2}$ and output ...
69 views

how to verify subset of hashes from hash list

I need to verify a couple hashed (SHA256) integers from a list of approximately 50 hashed integers in a message. The list can be divided into groups. The (plain) integer data is not in the message, ...
31 views

Are there good options for password hashing in embedded systems? These systems often cannot afford slow has functions. I can think of a few approaches: Store the (hashed) passwords in a HSM that ...
36 views

How would you name and/or describe this algorithm?

First up: this is not a decoding request or anything. This is about terminology. Twice per year, we email another department to ask for a new licence file for their software. They are always slow to ...
56 views

Q: Relevance of physical layer security to cryptography

I found that there are quite some active research activities in a field named "physical layer security", with in particular some types of codes that apparently are different from those commonly ...
42 views

Example of Projective Coordinates

Given the affine form of coordinates $(x,y)$ such as $(5,3)$, if I want to convert $(5,3)$ to projective coordinates $(x,y,z)$, should the form of point be $(5,3,1)$? It is triplet not a point, right? ...
76 views

Can we break ECDLP with this machine?

Let $P$ and $Q$ are two points of NIST elliptic curve $E$ (defined over $F_{2^m}$ with prime $m$) and $k$ is a private key such that $k.P=Q$. Also we have a machine that is able to leak some ...
39 views

What is the canonical way of creating merkle tree branches?

I'm currently looking into creating some compact merkle tree branches to prove that a given hash was included in a given merkle root. My initial thought was to list the leaf, the merkle root and all ...
50 views

compact rsa private key format

As shown in Why does my SSH private key still work after changing some bytes in the file? a typical RSA private key file contains. The public modulus $n$ and exponent $e$; The private ...
42 views

Recover secret $x$ when $c\equiv m^x \pmod p$ with public $p$ (modified)

Given an encryption system where $c\equiv m^x \pmod p$, $p$ is a known prime, 1. Is it possible to recover $x$ with a known plaintext attack? Given $(p,\text{factorization of }\varphi(p),m,c)$ 2. Is ...
159 views

Zero Knowledge Argument for Subset Sum

What is the currently most efficient (interactive) zero knowledge proof/argument for the subset sum problem? The most recent relevant paper I have found is Efficient Modular NIZK Arguments from Shift ...
55 views

Cyclic group collision resistant keyed cryptographic hash function

I am self-studying cryptography from a book and have come across a really difficult question that's doing my head in. I would be very grateful if somebody can help me out here with this difficult ...
66 views

How to compute projective cordinate Z in elliptic curve cryptography?

I was working on affine coordinates and struggling with the computation time taken for operations and then I was advised to use projective coordinates so that mul-inverse operation can be avoided Can ...
46 views

authentication protocol questions/security

Disclaimer: I am the only person that uses my software. This is just experimental fun. I previously wrote a server/client that used the secure remote password protocol authentication. I had an idea ...
66 views

MITM Attack on Key Exchange Protocols

I was doing research on this attack and I am wondering, why is Diffie-Hellman always associated with such an attack? ​ Aren't other public key cryptography schemes vulnerable to the same kind of ...
41 views

Differential Cryptanalysis

How do I find the differential characteristics using techniques Shrinking ? How do I extract the key on Differential Cryptanalysis using the technique Shrinking in Blockcipher Algorithm? Shrinking ...
44 views

How do I prove that a bit by bit PKE scheme (that is IND-CPA secure) for an n-bit message is not IND-CCA-2 secure?

Gen generates Pk and Sk (l bits each), Enc encrypts m (length l) but by bit using each bit of Pk respectively, Dec decrypts ciphertext bit by bit using each bit of Sk respectively. How do I prove this ...
51 views

How to force an adversary to call a certain oracle?

Consider there is a protocol in real world, which uses a random oracle $\mathcal{H}$. In the ideal world, after the calling of $\mathcal{H}$ by some parties, intuitively I want the simulator gets some ...
36 views

StoredKey in Salted Challenge Response Mechanism (SCRAM)

In SCRAM (RFC5802, page 8) the client generates ClientKey to server, which is a derivation of the original password. This is communicated to the server in a secure ...
54 views

User revocation in Identity Based Encryption

I read several papers about user revocation in IBE recently. A common point is that when a user is revoked, some other valid users should also update their private keys. Does this mean that one ...
83 views

Deletion in RSA Accumulator

I am studying RSA Dynamic Accumulator and I have a question: why is simpler to calculate the new accumulator value after a deletion if is known the secret ϕ(n)? Is possible to calculate the deletion ...
39 views

David Chaum's anonymous credential

I am a newbie in cryptography (I know the basic RSA, AES stuffs) and am interested in anonymous authentication systems. Looks like David Chaum is the godly figure in the field. I see lots of people ...
19 views

What's the perfect chain length : number of chains ratio for rainbow tables?

I'm building a SHA-1 rainbow table to crack basic passwords (i.e. up to 10 character, 0-9,a-z). But I can't seem to calculate that golden ratio that would give me the most coverage. Also is there ...
25 views

Are there any real-world E-voting systems in use with the Paillier cryptosystem?

There are a lot of theories of Paillier cryptosystem with references to e-voting. Are there any real-world E-voting systems in use with the Paillier cryptosystem?
40 views

Are there any FHE-MPC schemes implemented?

I want to know if there are any publicly available multiparty computation schemes derived from fully homomorphic encryption schemes. An example would be the implementation of this scheme ...
69 views

If a PRG is constructed by iterating a PRF, is it backtracking-resistant?

Say we construct a pseudo-random number generator from a pseudo-random function $f$ (using some constant key $k$ and some initial value $v_0$). We do this by feeding the output block of the PRF back ...
31 views

I am currently trying to implement the pathORAM algorithm as describe in this paper: https://eprint.iacr.org/2013/280.pdf The paper states that with high probability, the stash size will be bounded ...