4
votes
3answers
115 views

Proof of non-membership on a merkle tree

Assume a user U and a server S. User uploads its data and wants later to perform an authenticity check. It also sends a merklee tree to the server. Lets say we would like the user to ask for a ...
5
votes
1answer
274 views

Affine Cipher over an Affine cipher

I would like to know your view about the title, encrypting a plain text with an affine cipher then encrypting that ciphertext once more using the same cipher, but of course different keys. Would it be ...
-1
votes
1answer
233 views

Should I use RSA encryption since RSA is said to be broken by NSA? [closed]

I am developing a simple web app that uses asymmetric encryption, but I am not sure whether to chose RSA for the reasons mentioned above. What are your suggestions? Also if I decided to go with RSA ...
3
votes
2answers
67 views

Are low security curves for ECDSA not supported?

I am working in a very bandwidth restricted environment, and we are looking to implement ECDSA digital signatures. Although they are no longer recommended, we might be looking to use curves that are ...
3
votes
1answer
74 views

Containers for secret key

What 'container' is used normally to store/transport secret keys (for symmetric algorithms)? I have come across PKCS12 format where a public key certificate as well as a private key can be bundled ...
7
votes
1answer
557 views

What is difference between meet in the middle attack and man in the middle attack?

From my understanding man-in-the middle attack works as follow: Alice and Bob agreed to use Diffie-Hellman using $a$ and $q$. Alice sends $Y_A$. Before it reaches Bob, Charlie ...
1
vote
1answer
247 views

Difference between AES CMAC and AES HMAC?

Can someone elaborate on how 'signing' is done using AES- CMAC and AES-HMAC? HMAC Signing as I understand: Compute the HMAC( Hash the key and the input concatenated in a special way) Verification: ...
6
votes
1answer
92 views

Generating a key to use with AES

I'm going paperless, and I want to encrypt the documents that I scan. I'd like to use CommonCrypto to perform AES-XTS encryption on each file. I'm a software engineer, and I like the idea of being ...
3
votes
1answer
145 views

Can a book cipher be cracked without key?

Book cipher works this way : Choose a reference book. For each word find its position in the book. replace each word by its coordinates (ie: 2,3,4 = page 2, 3rd line, 4th word). How would ...
2
votes
0answers
74 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 ...
1
vote
1answer
157 views

Simplied DES why 10-bit key?

In Simplified DES algorithm, the plain text is 8-bit & the key is 10-bit, why is that, why can't both be of 8-bits each?
3
votes
1answer
61 views

Faster alternative to HKDF

HKDF is used in one of my projects to derive separate keys from a common master key. But profiling has shown it to be the performance bottleneck under certain circumstances. Is there any faster ...
1
vote
0answers
15 views

References for cascade [closed]

I have found many sources against cascading encryption, however I am having trouble finding arguments FOR using cascading. AES-256 + BlowFish + RC5 etc... each with a different key. This is for ...
0
votes
0answers
15 views

Are the ECDSA public keys of a stable/fixed length relative to curve size? [duplicate]

I am working in an environment with strict bandwidth requirements, and we need predictable bit lengths of the stuff we send. We need to broadcast ECDSA public keys, and we are using OpenSSL to ...
2
votes
1answer
71 views

Can I shorten the large ECDSA public key output file from OpenSSL?

I am working in a very bandwidth restricted environment where I from time to time have the need to distribute public keys. The distribution happens in bit format, so there is no need for encoding, at ...
3
votes
2answers
144 views

Understanding the length b used in MD5

I am trying to understand MD5 hash algorithm from the link http://www.ietf.org/rfc/rfc1321.txt At first I was not able to understand padding of MD5. Then I asked a question in this link: To ...
2
votes
0answers
37 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 ...
-3
votes
1answer
51 views

1 bit shannon entropy CPU instructions?

It has been proved, that the xor operator is suitable for entropy accumulation, due to its theoretical shannon entropy of 1 bit. There are six truth tables with ...
3
votes
1answer
59 views

Does a “commutative” asymmetric system exist?

Completely crypto noob here. I'm looking for a cryptosystem made of a func f + key1 + key2 such that they satisfy: g(f(msg, key1),key2)=msg g(f(msg, key2),key1)=msg key1 != key2 Does such a ...
4
votes
0answers
44 views

Security parameter p =O(n)

In many homomorphic encryption scheme, a security parameter is calculated as p =O(n). How to use the complexity order as values? Is there any specific method with an appropriate example?
3
votes
1answer
143 views

Is finding collisions in a part-hash not often enough a bad problem?

My situation: I've been working now for a couple of months on my own unique hash function, I've changed it many times and had two main versions but I won't bore anyone with the details of my work; at ...
1
vote
2answers
84 views

Homomorphic encryption diagram and trouble about a paper

I'm reading a paper based on Homomorphic Encryption: “Fully Homomorphic Encryption over the Integers: From Theory to Practice” (PDF). Now, I need a diagram of this algorithm if possible with all the ...
2
votes
1answer
296 views

Periodic One Way Function

Is there any notion of a periodic OWF? I.e. an OWF $f$ that on every input $x$ in its domain it holds that $f(f(f\ldots f(x))\ldots )=x$ when $f$ applied many times, each time on the previous ...
6
votes
2answers
198 views

Scrypt not “old enough” to be safe?

I just check all the questions with scrypt tag about that and usually it's said that scrypt is nice in theory and theoretically better than bcrypt and PKDF2, but it's too young to be "completely ...
5
votes
0answers
78 views

Performance of ECDSA, ECKCDSA and ECGDSA

It is proven that ECDSA algorithms are faster in key and signature generation compared to RSA. In addition, the signatures are much shorter. However, I would like to know the performance difference ...
1
vote
0answers
70 views

PBC library: group of composite order for pairing operation

How to generate composite order group using PBC library? With PBC library, element_init_G1(g,pairing) statement creates element $g$ for group of prime order. I want ...
2
votes
1answer
50 views

Is the length limit of AES-GCM per key or per (key, nonce) pair?

AES-GCM has a limit on the length of the plaintext it encrypts: $2^{39} - 256$ bits. But is this limit per key or per (key, nonce)? That is, if I encrypt a message with the maximum length, and encrypt ...
2
votes
1answer
83 views

Why is CBC-MAC with length appended not secure?

I've just read about CBC-MAC for the authentication of arbitrary length messages. In particular I cannot figure out why appending the message length before computing the MAC yields a non-secure MAC. ...
5
votes
1answer
435 views

To understand a fact related to padding in MD5

I'm trying to understand to padding process of MD5 from the link: http://www.ietf.org/rfc/rfc1321.txt In this link I have found the following description of padding: The message is "padded" ...
2
votes
2answers
141 views

Collision free one way function

I was playing with a function that I think is collision free and uninvertible assuming the hardness of integer factorization. I am unfortunately not as skilled at math as I would like to be, and do ...
1
vote
1answer
52 views

Can homomorphic operations on many different ciphertexts be multiplied by a same constant?

Assume Alice encrypts messages $m_1$,...,$m_n$ using secret keys $k_1$,...,$k_n$ on a homomorphic encryption scheme (BHHO), so she would get $c_1=Enc_{k_1}(m_1)$,...,$c_n=Enc_{k_n}(m_n)$. Then Alice ...
2
votes
0answers
45 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 ...
1
vote
0answers
63 views

Encryption used in a commercial software product [closed]

I found (through some reverse-engineering) that the following encryption scheme is used in a commercial software that is quite widely used in Germany (Security by obscurity at its best). I have the ...
5
votes
0answers
69 views

Why is AES-SIV not used, but AESKW, AKW1?

I'm trying to investigate different key wrapping algorithms for my implementation. I've noticed that AES-SIV is very rarely implemented by most of open source libraries. Most of them implements key ...
1
vote
1answer
41 views

Elliptic ElGamal Public Key Cryptosystem doubt

I need an example of Elliptic ElGamal Public Key Cryptosystem. I have been trying with some values but I don't get the right solution. I have $p=13$, the elliptic curve $E:y^2=x^3+11x+7$ and a point ...
7
votes
2answers
384 views

Need for salt with IV

I have mainly referred to this question. Definitely in case of using a salt, IV has a use of adding randomisation to each and every key. But isn't it redundant in case of using an IV to use a salt? ...
2
votes
1answer
63 views

Proven secure scheme under random oracle

Currently I am trying to understand random oracle model in order to make a small presentation about it but I seem to be very confused about it. Since it's an hypothetical model without a real life ...
2
votes
1answer
57 views

How to test an implementation of a homomorphic scheme?

I want to implement the following homomorphic encryption scheme from On-the-Fly Multiparty Computation on the Cloud via Multikey Fully Homomorphic Encryption by Lopez-Alt et al. I use C++ and I want ...
0
votes
1answer
59 views

Steganographic embedding of an RSA-encrypted message into an image

The goal is to combine the RSA encryption system with the LSB steganography system in a BMP image. Since every pixel of the image is an integer between 0 and 255, if we choose $p$ and $q$ such that $N ...
2
votes
0answers
41 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 ...
3
votes
2answers
65 views

(Non-) Perfect Secrecy of Vernam Cipher Using $E(m) = m \oplus k \oplus \operatorname{rev}(k)$

Given the cipher $$E(k, m) = m \oplus k \oplus \operatorname{rev}(k)$$ where $\operatorname{rev}(k)$ is the reversed binary of $k$, how would one prove that the cipher is not perfectly secret. I ...
45
votes
1answer
3k views

Why does my SSH private key still work after changing some bytes in the file?

I (for a test) just randomly altered a private RSA key by opening it up in Vim and changing a few bytes. It is the private part of an SSH key pair used for logging in on a remote system. Puzzlingly, ...
2
votes
1answer
63 views

Which values are used for an elgamal cryptosystem public key?

I know that – within the elgamal cryptosystem – the values of $a$ and $b$ are public. But which values are used to create public keys?
6
votes
4answers
482 views

Why can’t the public key exponent in RSA be negative?

I am looking at why certain public keys in RSA can't be used, such as: 2 and all other even numbers (since $\gcd(\phi,e)$ must equal 1) 1 (since the cipher text would equal the message) 0 (since the ...
10
votes
3answers
235 views

Plain text size limits for AES-GCM mode just 64GB?

Based on NIST SP 800-38D section 5.2.1.1, it seems that the maximum length of plaintext is 2^39-256 bits ~ 64 GB. We've got 100+GB files in genomics that need to be GCM encrypted so are concerned ...
1
vote
0answers
67 views

What can I do to improve my encyption method [closed]

I'm new to cryptography and I want to learn more. For me, the best way to learn about something that I have no experience with is to experiment and I've coded a very basic approach to a simple ...
8
votes
1answer
109 views

A general definition for cryptocurrencies

I am trying to find the definitions to several terms related to digital currencies. Unfortunately, I am always ending up on Bitcoin-oriented pages and websites which only take Bitcoin itself into ...
6
votes
3answers
552 views

What is the advantage of digital signatures over message authentication codes?

Studying for CISSP these choices seemed limited: What is the advantage of digital signatures over message authentication codes? Digital Signature provides integrity verification while ...
3
votes
1answer
65 views

Is it secure to use hexadecimal data for IV instead of raw binary?

Is it safe and secure to use a function like bin2hex (which converts binary data to hexadecimal) on the binary output of functions like ...
6
votes
2answers
104 views

RSA: Proving that $p+q-1 < 3 \sqrt{N}$, where N = pq and p,q are prime?

I'm doing some research into attacks on the RSA cryptosystem and have stumbled across Wiener's attack. Within the proof there exists the statement "$p+q-1 < 3\sqrt{N}$". No proof is given for ...

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