0
votes
0answers
4 views

Using a hash (like SHA-256) vs AES as the source for pseudo-random values in Feistel network?

This question is in relation to Wikipedia article on Format Preserving Encryption It says the following "It is also possible to make a FPE algorithm using a Feistel network. A Feistel network needs ...
0
votes
0answers
4 views

Attribute Based Encryption

Could someone give me a link to a book, PDF or video that could help me learn all about ABE. I have been trying to find a source that could summarize the whole topic but was unlucky. I would be ...
2
votes
0answers
14 views

POODLE attack on TLS 1.2

The POODLE attack uses the way block ciphers in CBC mode are decrypted in combination with the packet's padding to determine some byte's value. From what I understand, even TLS 1.1 can be vulnerable ...
6
votes
1answer
97 views
+100

Key Size for Symmetric Homomorphic Encryption Over the Integers

In the paper Fully Homomorphic Encryption over the Integers, it mentions a symmetric key scheme on page 1 and 2. Key Generation: Pick a random odd number $p \epsilon [2^{N-1},2^N)$ Encrypt A Bit m: ...
6
votes
3answers
181 views

What is stopping someone from saving encrypted info, and decoding it later?

When I send encrypted data to a website, using public key encryption, what is stopping someone who is listening from storing my encrypted data, and decryption it in a few years after they have ...
1
vote
0answers
12 views

Hash-values's length in identification schemes

I am trying to understand the impact of applying a hash function in an identification scheme. It makes reference to the publication "On the length of cryptographic hash-values used in identification ...
1
vote
1answer
85 views

The encryption scheme is secure?

I have a scheme and I don't know that this scheme is semantic security or not. Secret keys $\{s_1,s_2, x_1,x_2\}$ and public parameter $p$ (large prime number). Encryption E(m): $C_1 = s_1m + x_1k ...
8
votes
1answer
37 views

Edwards / Montgomery ECC with Weierstrass Implementation?

So let's assume I want to perform Ed448 or Ed25519 digital signatures or want to perform a DH key-exchange. Assume further that those curves (Curve448 or Curve25519) are required. But the problem is, ...
2
votes
0answers
21 views

DSSP reduction to DSSI

In “Towards quantum-resistant cryptosystems from supersingular elliptic curve isogenies" by DeFeo, Jao and Plut, a reduction from the Decisional Supersingular Product (DSSP) problem to Decisional ...
4
votes
1answer
244 views

PBKDF2-SHA512 - Does a Big Salt Decrease Security?

I use PBKDF2-SHA512 with an iteration count of 128,000 to hash my passwords. I use a CSPRNG to generate a salt per password. However, I am unsure about the ideal size of the salt. I have read a lot of ...
2
votes
1answer
138 views

Straightforward method for hampering frequency analysis on deterministic encryption

I'm brainstorming some different ways of making deterministic encryption more secure. I want to use deterministic encryption to preserve searchability over the keywords in a document set. However, I ...
2
votes
1answer
104 views

Is a strong block cipher usable as a strong sponge function?

From the literature, it looks like the security proofs of sponge functions depend on how well they approximate a random permutation, Since a block cipher also ideally behaves like a random permutation ...
2
votes
2answers
85 views

What practical uses can random hash collisions be put to?

Using magic, I've built a machine that instantly generates hash collisions. To try it out, I set the dial to SHA256 and typed in "e7cf3ef4f17c3999a94f2c6f612e8a888e5b1026878e4e19398b23bd38ec221a". I ...
4
votes
2answers
78 views

Randomness in Public Key Encryption

For a scheme to be at least CPA secure, one has to randomize the scheme. In case of a secret key encryption scheme, the used randomness will typically become part of the cipher text as in the case of ...
0
votes
0answers
28 views

Whar are the differences between curve NIST P-521 and Edwards E-521 for signature?

I implemented and used the P-521 curve for ECDSA. Signatures are 132 bytes long. It seems that Edwards E-521 is safer but I did not investigated very deeper. What is its signature length ? How is it ...
3
votes
0answers
59 views

Proving set membership in less than log(N) bandwidth

I have an unchanging set of unique items, and I want my server to show one of those items to a client, then cryptographically prove that the item is part of the set. How I do this currently: ...
1
vote
1answer
49 views

Can a tree hash with leaf-size of 1 byte support verification of content with elided ranges, at a cost of at most 2 supplied internal-node hashes?

Perhaps someone can confirm my intuition: A tree hash with leaves of size 1 (for example Blake2 in a tree-hash mode) would of course not be very efficient. But it seems that it might be a suitable ...
9
votes
1answer
34 views

What are the roles of the simulator in simulation based proofs

I'm trying to better understand simulation based proofs in the UC model - but the guidelines to construct a simulator confuse me. To my understanding, the simulator is activated in two ways: ...
1
vote
0answers
10 views

End-to-End (Point-to-Point?) Email encryption [migrated]

I'm looking into providing security for the email server I recently deployed, however the subject matter is a touch more complex than I anticipated and I would appreciate confirmation or correction of ...
0
votes
0answers
8 views

How do I create a PKCS#7 or CMS enveloped signature in python? [on hold]

There doesn't appear to be PKCS#7 or CMS support in pyCrypto. Ideally, there will be a call that will create return an enveloped signature given a signer certificate, an RSA private key and a payload ...
2
votes
2answers
126 views

Is it okay to include relative time for true random number generation?

Similar questions have been asked regarding use of time in true random number generation, but I'd like to consider using time as just one source of entropy, complementing others. True random number ...
1
vote
2answers
94 views

What are the required security properties for salts?

I was recently thinking about password hashing (maybe caused by the PHC progression). I started to think a little more about it and got stuck at this question: What security properties do ...
1
vote
1answer
57 views

Inverse public-key encryption

I'm in the need of an inverse public-key encryption method where you encrypt with the private key and decrypt with the public key. In other words an asymetric encryption where you can't generate the ...
4
votes
2answers
100 views

How to hash similar strings to the same hash value?

Suppose that $s_1$ and $s_2$ are two stings that have a small hamming distance. Is there a preimage resistant "hash" function ($H$) that can map them to the same value i.e., $H(s_1) = H(s_2)$?
3
votes
2answers
912 views

Generate RSA-2048 private key for a VERY fast decryption (don't care if it will be unsecure)

Given public standard RSA exponent e = 65537, is there any (d, n) pairs so that RSA decryption becomes a trivial operation? The modulus n must be no less than 2048-bit. The goal is to get a real ...
7
votes
3answers
150 views

What is a Key Derivation Function?

From Wikipedia: In cryptography, a key derivation function (or KDF) derives one or more secret keys from a secret value such as a master key or other known information such as a password or ...
5
votes
0answers
74 views

Using same modulus for RSA

I know that there exist some attack when using same modulus. Can two different pairs of RSA key have the same modulus? RSA cracking: The same message is sent to two different people problem But ...
1
vote
0answers
23 views

Open source code about the basic Quisquater-Piret DFA of AES-128 [on hold]

Where can i find open source code about the basic Quisquater-Piret DFA of AES-128? Are there any websites sharing the code about such physical attacks?
4
votes
3answers
409 views

Block cipher fixed points (plaintext equal to ciphertext)

A block cipher is a bijective map from the set of possible plaintexts to the set of ciphertexts, which are the same size and might as well be considered the same thing: $\theta: S\to S$. In this there ...
0
votes
0answers
32 views

Can a block cipher encrypt the message to itself (plaintext equal to ciphertext) [duplicate]

The result of the cipher should be indistinguishable from random, but can it happen that cipher produces the ciphertext that is equal to the plaintext as it also lies in the corresponding space? I ...
6
votes
3answers
781 views

CBC - a canonical mode, even though there are streaming modes

Why is CBC considered the canonical mode when there are streaming modes available such as CFB and OFB? One thing that I can think of is that in CBC you can easliy do range-based decryption. All you ...
5
votes
1answer
57 views

Where is CFB-MAC defined?

I can find a couple of descriptions of using CFB mode to create a MAC, but cannot find any standard or papers analyzing its security bounds. Is there a standard for CFB-MAC? Where can I find an ...
3
votes
2answers
35 views

Chosen plain text and chosen ciphertext definitions clarification

I am trying to understand a concept of CPA and CCA attack and I cannot get one thing from the definition. If an attacker can execute a CPA attack for something like Send 100 dollars to attacker that ...
2
votes
1answer
62 views

Is there really any way to nullify or avoid MITM attacks?

The question pretty much sums it up. Is there any way to make an attacker who is successfully performing an MITM attack to actually not be able to read or change the messages? Assuming there is no ...
0
votes
0answers
26 views

In HMAC-MD5 Implementation, why “i_key_pad” and “o_key_pad” if They Are Public and Constant? [duplicate]

Please Consider: English is My Second Language This Wikipedia article on HMACs shows a part of a HMAC-MD5 implementation making use of i_key_pad and ...
1
vote
1answer
39 views

Authenticating with a document

Hope you're having a nice day. I need to implement an authentication system between a "document" (it's not exactly a document, but an object without any computing capacity, only able to store ...
2
votes
0answers
72 views

How to break this PRNG encryption scheme? [on hold]

Suppose we have the following symmetric algorithm: key = random bits G = PRNG(seed: key) input = [0,1,1,0,1,0,0,0, 0,1,1,0,1,0,0,1] // "hi" in ascii The key can ...
3
votes
2answers
73 views

Does CTR mode yield a PRF?

Can the keystream generated by CTR mode be considered a pseudo-random function? I give more information. Assume $f$ is a PRF. We define a function which takes 2 inputs, the desired length, and an ...
1
vote
1answer
20 views

TLS Handshake : Server authentication or only Server ‘s Certificate authentication?

I have some difficulty understanding the way in which the Server is really authenticated by Client in TLS handshake (in case of using RSA key exchange). When Client receives Server ‘s Certificate and ...
3
votes
1answer
46 views

NTRU test vectors

Where can I find NTRU test vectors? In some research work in 2001, it is stated that test vectors were not publicly available at the time. Then in this ESSS1v2 standard under IEEE1363 here , the ...
3
votes
2answers
43 views

How strong can multiple encryption be?

Suppose I encrypted a homophonic substitution cipher at the level of syllables, trigrams, digraphs, and individual letter with a Vigenere cipher using the keyword cryptography. I would then encrypt ...
5
votes
3answers
762 views

With a true random number generator at hand, how to implement one-time pad?

I have a Raspberry Pi single-board computer that happened to have an hardware true random number generator, based on some quantum effects on the processor silicon, baked into its BCM2835 chip and I ...
2
votes
1answer
35 views

Is there a practical security difference between OTP with letters and OTP with numbers?

Is there a practical security difference between OTP with letters and OTP with numbers? If, for instance, I encrypt a letter message, using Tabula Recta, with a random letter key THISI SATES TXAAA - ...
9
votes
3answers
1k views

Webcam random number generator

I have a question about random number generators. I have read from a real random number generator, based on a webcam ("randcam"). My problem is, that I do not really understand how the generation of ...
-3
votes
0answers
35 views

what´s this is???? What it says here ? And how you could change it, or edit it? [on hold]

54c2c00ddf08dd17d5337c9f082797850b720a7be88bb6dfa646eb07740748c8ca08d6a910b4c1e5e73d84f0651c75718e80ec760ba356b2ea41b95e480127130afebd1bb27e019abb868a21a2ff9231807fa88c23fe3e0e3ff76d88f9949b0493592046 ...
3
votes
1answer
24 views

Given occasional LFSR samples can the next sample be computed?

Suppose I have access to an LFSR generator output used in a radio communications system, with the LFSR being used to authenticate devices. The system cycles an internal unknown length LFSR (greater ...
12
votes
1answer
4k views

ECDSA vs ECIES vs ECDH

Recently I started studying Elliptic Curve Cryptography and I just loved it. I want to transfer some big data (like 3KB), What is the best method, ECDSA, ECIES, or ECDH (and why)? I am confused, how ...
1
vote
1answer
99 views

Proving an encrypted message contains (but does not 100% consist of) a plain-text message?

I have keypair (u,r), and two pieces of data, X and Y. I reveal X publicly but keep Y secret. Y has high entropy. I then concatenate X and Y, into Z. I encrypt Z, into "encrypt(Z,u) = Q". r is ...
2
votes
1answer
28 views

Can we use the authentication tag as Nonce / IV for the next message?

Let's assume we're in some scenario requiring transfer of large amounts of data. This means we can only use AES-GCM chunk-for-chunk as its maximal size is restricted to a few GiBs. This means we have ...
0
votes
1answer
57 views

How secure is this modified Bazeries Cylinder?

This device is a modification of the Bazeries cylinder, it has two stacks of 5 rotors which each bear two alphabets plus numbers 0-9, one in correct order and one in random order ( 36 characters in ...

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