# All Questions

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### Is standardizing a modified AES a good idea?

"Recently" the Ukraine standardized a new block cipher Kalyna, which according to the abstract of this paper (warning: the paper contains a lot of test-vectors) is basically a modified version of AES. ...
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### What is a man-in-the-middle attack (for instance in Diffie-Hellman)?

I'm new to cryptography and I just started learning about the Diffie-Hellman key agreement. I read that this system is vulnerable to a man-in-the-middle attack when used alone. What kind of attack is ...
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### I hashed my bag and in it I put… “Is there a hash for unordered items?”

(By items I mean hashable objects.) As an example (with obviously way too short hashes for readability), say I packed my bag and in it I put a shovel (hashed to ...
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### Pseudo Random Function

The definition of pseudo randomness that leads to pseudo random function talks about indistingishability of a key-ed function and a random function. i.e. The key-ed function family $\{F_k\}$ is PRF ...
180 views

### Suggestion : CRC vs SHA1

I need some suggestions about the use of the CRC in my application. I need to be sure about the BIOS run by the CPU. I have a FPGA between the BIOS flash and the CPU that sniff every read performed by ...
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### Why should the input value on a DPA attack be non-constant?

I actually was wondering if anyone could help me out with the following problem: Let's assume we are attacking the first SubBytes() operation on AES with the help ...
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### what do you mean by cost in encryption? [on hold]

What do you generally mean by cost of an encryption algorithm? how are they computed and how to compare the cost of two encryption algorithms?
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### How often does RSA-OAEP have a leading zero?

We are working with a third party vendor who is very tight lipped about their security protocols, and one of our customers who used this vendor's products is claiming that approximately one in every ...
42 views

### Theoretical Mathematics & Cryptography [on hold]

I read in Bruce Schneier's book ,"Applied Cryptography", that cryptographers need to study theoretical mathematics in order to be good at their job. Why is that?
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### Is this client-side password hash scheme secure?

I want to build an app that uses client-side encryption for storing encrypted data on the server. A user-specific master key would be used, so to easily share it between devices a encrypted version of ...
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### Creating disk image of encrypted disk [migrated]

I'm Fedora 21 user for some time and I'd like to create disk image to escape installing everything over again when something fails. I have encrypted storage and that fact makes me wonder. How do I do ...
51 views

### Does authenticated encryption add any protection to a signed digital envelope?

The general scenario of hybrid encryption is to use public key cryptography for the exchange of a one time session key that can be used for the encryption of the plaintext with a symmetric encryption ...
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### Cryptographic Disk wiping with quantum random data?

I was thinking about using 4 Quantum Random Number Generators working at the same time to create a secure disk wiping system. Basically feed the random bits into to an approved DRBG then through an ...
2k views

### “123456” and “password” as crack standards

I know that when we encrypt, we use standard encryption technologies and to store data it's often stored as a hash. By encrypting a common password, for example "password" using ...
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### What is SRP-Z form?

The stanford license for SRP says: ...
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### Why do some programming language API's not support private key passwords? [migrated]

Two questions: I've recently started building a basic Go web-server, and noticed that the API for starting a TLS web-server does not support a symmetrically encrypted private RSA key. The API is ...
41 views

### Fast mental encryption algorithm? [duplicate]

Are there any algorithms that exist to encode messages written with pen and paper such that the messages can be encrypted/decrypted mentally? For example, Bob thinks of the text "This is my ...
18 views

### BKSQ Block Cipher implementation [on hold]

has anyone a working implementation of BKSQ block cipher? (preferably in c)
59 views

### Proving membership of a group without revealing identity

I have an interesting problem for which I've failed, so far, to find an elegant solution. Imagine that a user needs to repeatedly prove to public observers that they are a member of a trusted set ...
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### Simulation aborted because the adversary doesn't use the random oracle

I'm trying to construct a proof for an encryption scheme in the Random Oracle model. This encryption scheme is like a PKE scheme but with an additional function that kind of "alters" ciphertexts ...
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### EdDSA Signature Algorithm - hash of secret key

Why does EdDSA use the (SHA512) hash of the secret key as the exponent for the public key rather than using the secret key value directly? This seems inefficient and I can't see how it adds any extra ...
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### Source for PKCS#11 Header Files

Is there a known authoritative source for the ANSI C header files for PKCS#11 Cryptoki? Specifically, I am having trouble locating pkcs11.h, pkcs11t.h, and pkcs11f.h for v2.30 and v2.40. Are there ...
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### Ideas for non duplicate cryptographically secure numbers

My Boss asked me this today. I am not a math major. He needs to generate 50 billion non-sequential non-duplicate (no collisions) cryptographically secure random numbers. I work in GO. Any ideas?
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### RSA function over $Z_t^{*}$ where $t$ is prime

RSA function is defined over $Z_N^{*}$ where $N=pq$ with $p,q$ primes. A public key is a pair $(N,e)$ and a private key is $(N,d)$ where $d=e^{-1} \mod \phi(N)$. Assume that RSA function is defined ...
62 views

### ElGamal scheme attack when one message is known and ciphertexts are intercepted

Let $G$ be a finite cyclic group of order $p$ and let $pk = (g, h=g^a)$ and $sk=(g,a)$ be Bob's ElGamal public/secret key pair in $G$. To encrypt a message $m$, a random number $r$ is selected and a ...
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### What happens if no final subtraction is done in Montgomery multiplication?

I'm doing Montgomery arithmetic modulo $N = 2^{255}-19$ for the Curve25519, picking $R = 2^{256}$ for Montgomery. After multiplying two numbers $0 <= A,B < N$ in the Montgomery representation ...
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### “AND” concatenation of two secure PRGs

Let $G: \ K \rightarrow \{0,1\}^n$ be a secure PRG. Define $G'(k_1,k_2)=G(k_1)\wedge G(k_2)$ where $\wedge$ is the bit-wise AND function. Consider the following ...
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### Double the key in block cipher - which approach is better?

Assume than you have a block cipher $E(k,m)$ for which the only attack exists has complexity of $2^{64}$. You consider to double the key size by either: $E'_1(k_1,k_2) := k_1 \oplus E(k_2,m)$ ...
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### TLS encryption with a self-signed PKI and Python’s asyncio module

I want to enable TLS encryption with a custom / self-signed PKI for a self-contained distributed system built with Python 3’s asyncio. I’ve read Python’s ssl docs as well as several tutorials: ...
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### How to multiply two field elements generated by bilinear paring map? [on hold]

I wish to clarify how to multiply two field elements generated by bilinear paring map. The following is an example where I need to multiply e1 and e2. is it possible? If yes, then how? FieldElement ...
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If I have an original file and a WinRAR password protected .rar file containing that file, than can I extract the password?
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### Forgery attack on OCB

When using same nonce in OCB mode of authenticated encryption, how forgery attack can be done?
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### Establish authentication

I have designed a basic authentication scheme where two nodes will mutually authenticate that other holds a shared secret. I have very limited RAM/ROM (its on uC) and bandwidth. Here it goes: ...
43 views

### HMAC-SHA1( secret key ) with header of a transmitted file

Given: an AES-128 secret key (ASecKey) encrypts a file (CBC mode). (Assume good random) Is is insecure to append (include) an HMAC-SHA1 of ASecKey to file? Purpose: The receiver can then quickly ...
134 views

### What is a “lattice” in cryptography?

There are some questions here concerning lattice-based cryptography and this kind of cryptography seems to be especially useful if quantum computers are assumed to exist. When reading such questions ...
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I need some advice as I have been unable to find anything useful via the web - (Google search). I have used the application EventGhost so as to create a custom shell, that I run using the Windows 7 ...
39 views

### Security of MSS

I have started reading about the Merkle Signature Scheme. I am a little confused about why it is believed to be secure against quantum attacks, couldn't the hash function be attacked? What would make ...
46 views

### Block Ciphers - Standardize plain text

I need to use AES-128 to encrypt a plain text about 720 bits. Is it correct to say that – in this case – the plain text will be divided in 5 blocks of 128, the result will be equal 640 bits, and the ...
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### Can I use HKDF to improve security of HMAC used with weak hash function?

I am writing a framework which encrypts/decrypts files (or streams, in general) with symmetric key using block cipher (for example, AES). To authenticate encrypted file, I use HMAC, which is ...
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### RSA Signature Forgery

We all know that x509 certificates carry a signature that represents the certificate digest encrypted by the private key of the issuer. I believe that the digest is encrypted only providing one ...
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### Logjam-style attack on Factoring?

We're all aware of the Logjam attack, which is known as "FREAK on discrete logarithms". Now the attack works by doing a large pre-computation step, which needs only to be done once per field and then ...
32 views

### Getting the encryption/has algorithm used for modem configuration file [closed]

Hello guys I have backed up my modem configuration file and found the username and password is in clear text; the files shows the username and the password is : ...
58 views

### Do all attacks against PKCS1 v1.5 encryption require an oracle

As far as I know, all attacks against RSA PKCS1 v1.5 require an oracle; is that true? Or are there any other attacks against it which are able to break it without an oracle? Background: I need to ...
29 views

### HMAC for encrypted authentication token: recommended iteration number [duplicate]

In the web application I use 10,000+ iterations for hashing passwords stored in database (random salt and all). Password-related operations are not frequent enough to create a noticeable performance ...
28 views

### How can a lattice attack be applied to ECDSA signatures?

The aim is to check if it is possible to break the ECDSA cryptosystem under the following criteria. Suppose that each ECDSA signature is generated by using the GLV method for point multiplication ...
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### Transform RSA private key to ssh-rsa public key [closed]

I am generating a RSA key pair and write it to disk. I would like to transform the public key to look like this: ...
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### How to write automaticaly server generated keys into a file? [closed]

There have a server program, which generate keys for client. I want to store these keys into a file. I implemented the server and client program in python.. When server run each time for a user, the ...
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### Derive cipher IV and cipher Key using PBKDF2 with random salt?

It is said that cipher IV does not have to be secret and the only secret component of the encryption scheme should be a cipher key. Question: is it safe to generate IV using PBKDF2 function, which ...
I've been thinking about a geometric picture for El-Gamal. The idea is to understand the set $\{(my^{x},g^x) \mid x \in Z_p\}$ (the set of encryption of $m$ for fixed $g$ and $y$) by taking the ...