5
votes
2answers
211 views

Is my id obfuscation algorithm secure?

I'm designing an id obfuscation system. My system includes: Embedded chips, each chip has a unique 32-bit address (id). Server Insecure low-bandwidth unstable one-way channels from the chips to the ...
1
vote
1answer
99 views

Rainbow tables, where have I got it wrong?

There seems to be some error in my understanding of the concept of rainbow tables, despite going through quite a bit of articles on it. Let me show what I don't seem to agree with. My plain text is ...
1
vote
1answer
110 views

Where do I truncate the bits in SHA 256 hash algorithm?

I'm implementing SHA-256 in PHP using strings. Where do you truncate in the algorithm? There are a lot of places where there's binary addition happening so the number of bits in $W(i)$ keep ...
1
vote
1answer
560 views

Is Curve25519-java secure?

I have only about 2 weeks of cryptography experience mostly in the form of questions on bitcoin.se. Is Curve25519-java up to date with current Curve25519 standards? Is Curve25519 itself secure? ...
2
votes
2answers
271 views

Can I construct a feasible stream cipher out of HMAC and a secure hash algorithm?

I have constructed a stream cipher from a secure hash algorithm and a HMAC. Here is a brief description of the algorithm: Let: (Actually Objective-C styled pseudo code) ...
5
votes
5answers
909 views

Is there a hash function with 2048bit output?

Is there a publicly available cryptographic hashing algorithm with 2048 bit output? The standard ones are "only" up to 512 bit (SHA-512, WHIRLPOOL). (2048 bits are 256 bytes, so it would be useful ...
5
votes
1answer
195 views

Attacking a hardware AES implementation if it leaks the intermediate round states

Let's say that we have a hardware AES implementation that, on request, will encrypt or decrypt a 16-byte block of data in ECB mode using a fixed key, but refuses to reveal its fixed key. In other ...
3
votes
3answers
3k views

What algorithm could/should be used to encrypt files for storage on untrusted servers?

I need an encryption algorithm that works fast on large files and doesn't increase the file size. It should use a key to encrypt/decrypt data. The files will be sent using REST and over HTTPS, but a ...
2
votes
1answer
173 views

The security of an encrypt-and-MAC

I would like to know what is the security of an encrypt-and-MAC with different keys for each transaction For example: the one-time-pad with $k_1$ and the HMAC with $k_2$ $$C = M \oplus k_1\\ MAC = ...
7
votes
2answers
588 views

Where can I get information on how to implement AES?

I want to write AES from scratch without using the built in libraries of java. I know there are hundreds of AES programs (and websites) out there but I can't seem to find a site that gives me the ...
2
votes
1answer
60 views

Number of keys when using symmetric and asymmetric encryption?

Quoting part of my homework/assignment: How many keys are required for secure communication among 1000 person if: Symmetric key encryption algorithm is used? Asymmetric key encryption ...
3
votes
4answers
423 views

Is there a symmetric-key cryptography based on key establishment techniques?

Most of the current key exchange techniques are based on public-key cryptography. Are there any key exchange/establishment techniques based on symmetric-key cryptography too? In my setup primary ...
3
votes
1answer
53 views

Session-specific Symmetric Key Derivation Using SHA256

I was wondering if there were any security implications of deriving session keys from a symmetric key using SHA256 in the following manner: $Ks = SHA256(Nonce||K)$, where $Nonce$ is the session ...
5
votes
2answers
118 views

ML/NN Cryptanalysis

Is it computationally plausible to use NN/ML to do any of the following tasks? "Real" cryptanalysis. Cyclic neural networks for extended computation, but break the hash all the way through. ...
3
votes
3answers
193 views

How feasible is word-level frequency analysis over English (or any language)?

Say I have some black box which, given any English word, deterministically outputs a token for that word. Assume our black box is implemented using strong cryptography, i.e. the hardness of reversing ...
0
votes
2answers
349 views

My SSH server public key is 2048 bits, but my account's private key is 4096. What is my effective security?

My SSH server has a 2048-bit public key. But my private key, for clients to login, is 4096-bit. In this case, do I have the brute force protection of 2048 or 4096 bits? My worry is that someone ...
3
votes
3answers
158 views

Advantages of 64-bit CPU smartphone

Advantages of having a 64-bit CPU vs 32-Bit CPU smartphone … 3. Complex Encryption. Improved Security: 64-Bit can process incredibly large numbers allowing you to better encrypt data against ...
11
votes
2answers
251 views

Can I use HMAC-SHA1 in counter mode to make a stream cipher?

Say I have an embedded device which is only capable of doing HMAC-SHA1 transformations (that device is, in fact, a YubiKey). Would it be secure to feed it like a block cipher in counter mode to get a ...
1
vote
0answers
370 views

How compared encryption algorithm in terms of efficiency

I want to compare two cryptographic algorithms. The first algorithm is RSA, and second algorithm is ElGamal elliptic curve cryptography. Now, I’m looking for a way to compare the speed of the two ...
5
votes
0answers
70 views

How dead is braid based cryptography

Braid groups has drawn the attention of cryptographers for a few years, as a promising platform for post-quantum cryptographic protocols. The security of the proposed schemes mostly relied on ...
3
votes
0answers
68 views

How can I fix a corrupted PGP file? [migrated]

I've encrypted a file with PGP but for "security reasons" I thought it would be good to damage the header and add some extra bytes so that even if someone finds it it won't know for sure it's a PGP ...
-1
votes
0answers
41 views

Strengthening security of an encrypted file against forensic detection [closed]

I have created a Truecrypt container for backup in the cloud, and I want to obfuscate to the greatest extend possible which software and algorithm was used to encrypt the data and to slow down any ...
2
votes
2answers
152 views

Chosen plaintext attack on textbook RSA decryption

Let $(n,d)$ be an RSA private key and $(n,e)$ the corresponding private key. Generate a secret random $r$ from $(\mathbb{Z}/n\mathbb{Z})^*$ Compute $C’ = C (r^e) \bmod n$ Submit $C’$ as a chosen ...
-1
votes
0answers
29 views

Big crunch, the Data way? [closed]

before exposing my problem I beg you all to excuse my bad english :).. let's take the bible book as an exemple with its 3,116,480 letters. (a file could also be considered as a book with its ...
3
votes
2answers
66 views

Hash or compression function in Merkle tree nodes?

Wikipedia says about a Merkle tree: Nodes further up in the tree are the hashes of their respective children. Usually, a cryptographic hash function such as SHA-2 or SHA-3 is used for the hashing. ...
4
votes
3answers
400 views

How to perform authentication without central server in P2P?

How can one be sure that the man who you're talking with is the one who you think he is? i.e. How can one perform authentication in P2P network without a central trust server or Certificate Authority? ...
3
votes
1answer
107 views

Luby-Rackoff theorem confusion

The Luby-Rackoff theorem states that if a round function is a secure pseudorandom function (PRF) then 3 rounds are sufficient to make the block cipher a pseudorandom permutation (PRP). PRPs are ...
-1
votes
0answers
91 views

A problem about zero knowledge proofs

$En()$ is a certain encryption function, $G$ is a cyclic group with order $q$ (a prime), $g,h$ are two generators of $G$. $\lambda_1,\lambda_2 \in Z_q^*$, $\mu$ has the relation $\mathcal{R} ...
0
votes
1answer
121 views

Known plaintext attack on ElGamal encryption

Assume that Alice uses Bob’s ElGamal public key ( = 2, Yb = 8) to send two messages $M = 17$ and $M' = 37$ using the same random integer $k = 9$. Eve intercepts the ciphertext and somehow she finds ...
4
votes
1answer
147 views

Elliptic Curve Crypto, is a distributed signing method possible using Shamir's Secret Sharing?

Note: A distributed signature scheme exists for RSA: Practical Threshold Signatures, Victor Shoup. Is it possible to adapt such scheme for ECC? A centralized signing machine is vulnerable to ...
1
vote
1answer
59 views

public key delivery without third party

I am currently working on an anonymous P2P file sharing application and I am elaborating some already existing solutions. Some of them allegedly provide point-to-point encryption using RSA ...
3
votes
2answers
193 views

Rely on NSA Suite B Cryptography?

NSA's Suite B Cryptography suggests some cryptographic algorithms for encryption, digital signatures, message digests and key agreements. The selected algorithms and their key size are suggested by ...
3
votes
1answer
89 views

Multi-key decryption

Let's assume I want to send a secret message to $N$ recipients in an asymmetric way. My message could be encrypted with $N$ different public keys $p_i$ one after another and send to each user ...
1
vote
1answer
230 views

How do the following new (2013) ECC curves compare in security or efficiency? [closed]

I read about the following "safe" ECC curves and notably, secp256 and all the NIST curves are marked as "unsafe" when compared to more modern curves. I need a curve for signing or encryption, (or ...
-1
votes
5answers
46 views

Why can't you decrypt an encrypted message with just the public key? [duplicate]

How does asymmetric crypto work? For example, if you use PGP in emails, you generate a private key that is known only to you and a public key, which is available to everyone. Is there a simple way ...
2
votes
2answers
68 views

Block-cipher based vs Hash based MAC

When it comes to MAC algorithms one can have many choices. CBC-MAC, CMAC, PMAC etc are some MAC algorithms that rely on block ciphers (ex AES) to generate a MAC. On the other hand HMAC is very popular ...
2
votes
1answer
314 views

Interleaving bytes to make an effectively larger block size

Will applying a 16 byte bit block cipher such as AES over a 256 byte block to in the following way result in a much stronger cipher:- Apply block cipher with first key digest to each 16 byte group. ...
4
votes
4answers
596 views

Subverting the key generation step in RSA public key cryptography

I am interested in the ways the implementation of an RSA key generation implementation can or cannot be subverted so that the subverter has an advantage, but the owner of the key, and the people who ...
2
votes
1answer
70 views

Are there any cryptographic flaws in my webhook signing process?

Out of band my services have exchanged secret keys. These secret keys are then used to prevent two things of the webhooks (HTTP calls triggered by Service A to Service B when an event occurs in ...
2
votes
1answer
43 views

Cryptanalysis of Nonlinear Table Lookup

I am trying to derive a symmetric key based on a master key, combined with a simple string. Based on my limited knowledge, it seems that something like PBKDF2 would do that for me in a well-defined ...
7
votes
2answers
532 views

Can you fake messages from recorded message-history?

Lets assume Eve has a lot of PGP conversation with Alice and records all those messages. Bob is also regularly communicating with PGP with Alice. If Bob doesn't care about not having a signature ...
4
votes
5answers
202 views

Using multiple secret keys

I have two secret keys. One is a secret key generated by OpenSSL (primary secret key). Second key is generated by performing one way hash operation to GPS co ordinates and time parameters (geo secret ...
-2
votes
1answer
32 views

How does the signature checking work in DKIM?

As far as I understand DKIM works like this: DKIM is not used to encrypt anything, the only purpose is to mark mails that are not really sent from the claimed domain as spam. the DKIM-enabled ...
1
vote
0answers
57 views

Implementation Attacks on Hashes

So I am familiar with attacking implementations of block ciphers via side channel attacks, cache-timing attacks, etc. What implementation attacks are there against hashes or hashed based functions ...
1
vote
1answer
52 views

Decrypting an Affine Cipher with known characters

I am trying to cryptanalyse multiple cipher–texts that I know are encrypted by different Affine ciphers. I have already analysed the frequency that each character occurs, and compared it to a ...
-1
votes
1answer
52 views

I am new to Cryptography and I wonder if one can Suggest me Beginner Projects [closed]

Sorry for this kind of a question, but I really like to learn and improve in cryptography. At the moment I am following online lectures from https://class.coursera.org/crypto-011 , can anyone suggest ...
-4
votes
1answer
76 views

How does Diffie-Hellman key exchange work? [closed]

I've been learning about cryptography lately and I'm failing to understand how Diffie-Hellman key exchange works. Can someone please demonstrate using mathematical notation (and if possible, ...
4
votes
1answer
69 views

$(k, n)$ threshold secret sharing to $(k+k', n + n')$ without reissuing all shares

Given a $(k,n)$ threshold secret sharing used to back up a secret (meaning that the dealer has access to the secret at all times), is it possible to update it to a $(k+k', n+n')$ threshold secret ...
-3
votes
1answer
65 views

Is encryption mainly using Diffie-Hellman Key Exchange?

I know how Diffie-Hellman Key Exchange works. Is this the main way of encrypting with PGP, ssh, ssl (https), DKIM, ...? I wonder if Diffie-Hellman is the clue to understand how encryption with ...
3
votes
2answers
179 views

Security issues of a MAC-then-Encrypt-then-MAC approach?

Encrypt-then-MAC does provide ciphertext integrity, but no plaintext integrity. With MAC-then-Encrypt it’s the other way around: Plaintext integrity but no ciphertext integrity. What comes to mind is ...

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