# All Questions

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### How is the EAX-mode used in EAP-PSK (RFC 4764)?

According to the specification of RFC 4764, contents in EAP's third message and fourth message are required to be encrypted by AES-128 in EAX mode (also called protected channel). In RFC 4764, the ...
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### Polynomial for secure communication

Can we use a polynomial $P(x)$ to securely communicate ? For example Alice & Bob agree on a degree of a polynomial. The value $x$ & the coeficients are generated from a seed using a hash ...
373 views

### Is RC4 a problem for password-based authentication?

This is a follow-up question to Does TLS use RC4-drop[n]?. As mentioned in section 6 of RFC4345, there are weak distinguishers for RC4 keystreams available that even work for keystreams that ...
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### Random decomposition of symmetric key

Considering a symmetric cipher (i.e : AES in counter mode), is it possible for any given key to be randomly decomposed into other keys without knowing the message or the ciphertext, such as : ...
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### Is it possible to match encrypted documents using user-defined search terms?

Suppose I am storing a number of encrypted documents in a database. I would like to make it possible to identify the subset of documents whose contents match user-specified search terms without a) ...
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### Blum Blum Shub vs. AES-CTR or other CSPRNGs

Following on from D.W.'s comments on a previous question, what properties does Blum Blum Shub have that make it better / worse than other PRNGs? Are there significant implementation difficulties or ...
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### Aes encryption -The relevance of static matrix in mixcolumns operation

Can someone explain to me the relevance of the static matrix used for the mixcolumns operation in aes encryption.i.e the relevance of why the byte is multiplied by 2 + next byte multiplied by 3 + next ...
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### Is a second preimage attack on MD5 feasible?

What's the practical status of MD5 w.r.t. second-preimage? Integrity of a piece of data is protected by an MD5 hash, itself assumed genuine. The data (and thus the hash) is known to the adversary. ...
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### MISTY1 Implementation error

I am trying to implement MISTY1. It's RFC, RFC2994, contains psuedocode that I basically copy and pasted into Code::Blocks. However, I managed to mess that up somehow. After 2 days, I still have not ...
685 views

### How to jusify {e,n} is a valid RSA public key?

I have a two set of key {36,77} and {50,117}, How can validate if it is a valid RSA public keys? Is there any simple method?
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### What are the dangers of predictable (repeated) plaintext structures?

When using a "good", modern cipher (specifically one that provides ciphertext indistinguishability), is it a problem at all if there is some well-known structure in all plaintexts? For example, ...
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### Can I use a key-derivation-function as the hash function H in SRP?

In the Secure Remote Password Protocol, the verifier must be stored on the server. In the case of a server compromise, an attacker could obtain these verifiers. If nobody reused passwords, this ...
239 views

### Stream cipher malleability

Considering a stream cipher that produces a ciphertext $c$ from a message $m$ and a key $k$ is it possible to apply operations (multiplication and/or addition) directly to $c$ without knowing the key ...
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### Are there any systems like SDSI / SPKI that are currently being developed?

SPKI / SDSI look interesting but appear to have fizzled out and died. Are there any modern competitors?
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### Relative security of a Vigenère cipher

Within a closed computer network, I am ciphering some plaintext data as an added security measure. This is below several other layers of protection. For various technical reasons, I am restricted to ...
404 views

### Does TLS use RC4-drop[n]?

According to many sources, the first few (n) bytes of the RC4 keystream are strongly biased, and therefore should be discarded before using the keystream to encrypt anything; this precaution is ...
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### Practical implementations of Multiparty computations [closed]

Are there any practical implementations and or software platforms to prototype applications based on MPC ?
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### Why does .NET's ECB mode implementation append a constant block to my ciphertext?

Consider the following code and output: ...
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### Why x00 is usually avoided in salt?

In .NET Framework, there is a cryptographic Random Number Generator (RNG) provider which enables to generate a cryptographically strong sequence of random bytes. This provider contain, among others, ...
186 views

### How many different keystreams can I produce with AES in Counter Mode?

I'm using a 64-bit nonce (incremented between the streams) and a 64-bit counter (incremented within a stream) for AES in CTR mode. How many different key streams can I produce with this setup?
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### Encrypt array of int for individual retrieval

I have limited exposure to cryptographic terminology, so please bear with me. My end goal is to encrypt integer IDs, before transmitting them to a web client in a list of search results, in a way ...
572 views

### SSTP MSCHAP-V2 Authentication before SSL or after SSL Session

So with the recent news that there's a lovely new tool to crack MSChapV2 packets. So the question I have is on a SSTP Connection is the MSChapv2 handshake encrypted pre SSL setup or post. Obviously ...
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### Why do we need extra hashing if we could use simpler scheme?

Lets say that we use init vector IV, key K and HMAC key H. Message is M. Mode of operation is CBC !!! We usually encrypt this way: ...
284 views

### What is the name of this kind of protocol

There is a communication protocol that I believe creates the equivalent of a one time pad, with the downside that the secret message must be transferred multiple times. The protocol is so simple that ...
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### Are there any multiparty homomorphic encryption schemes?

Are there any multiparty homomorphic encryption schemes ? Most of the literature is about two party schemes . Is there any generalization made for n party ?
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### What would be the most effective way to brute force a 16 char AES key?

I have a file that is encrypted in AES using a 16 char string. The string is (a-zA-Z0-9) and .,?!. Also, it only contains words ...
1k views

### How do I calculate CRC32 mathematically?

I want to calcuate the CRC32 algorithm using polynomials directly but I don't know how. I found the generating polynomial listed here https://en.wikipedia.org/wiki/Cyclic_redundancy_check. This ...
1k views

### Why does ROT13 provide no cryptographic security?

I can understand that ROT13 is not secure for obvious reasons, but I'm looking for the theoretical answer. Wikipedia says "The algorithm provides no cryptographic security.." What does it mean to ...
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### Should I use md5 for my new application?

MD5 is a very fast hash and its output is short and easy to store. Should I use it for my non-security-sensitive application? I don't think so, but I can't seem to convince anyone else that this is ...
1k views

### AES GCM symmetric encryption of data at rest in c#, ciphertext much longer than plaintext

I've written encryption/decryption routines using AES GCM. Code can be found here. I recently realized that the cipher text is longer than I believe it should be. It should add the tag and IV onto ...
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### Is just a bit of random, “fully random”?

I understand that hashing a datetime is a pseudo-random number, and not good in a security context. But what about hashing a datetime plus a truly-random but constant string (just a string that an ...
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### Adaptive Hash Functions: How to tell how many iterations were used?

If an adaptive hash function like bcrypt or PBKDF2 is used in hashing passwords, the number of iterations used in the hashing process can be configured. For a penetration tester or a malicious ...
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### Purpose of outer key in HMAC

From what I know, the HMAC constructions has two strength: It's resistant to length extensions Since the key is consumed before the message, the attacker does not know the initial state, preventing ...
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### Are mouse movement coordinates useful as a seed for a RNG?

Is it good to use a mouse movement as a 64-bit random seed for a Pseudorandom Generator like AES in Counter Mode? Should I only need to get the X and Y coordinates of the mouse movement?
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### Cryptographical formalization of computational privacy

Yesteryears problems of communication privacy has been well defined in cryptography through Asymmetric cryptography. Due to rise in Cloud computational model , computational heavy tasks are being ...
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### Pseudo preimage for a hash made from a cipher

Consider the Miyaguchi–Preneel construction: $H_0 = E(0,m_0) \oplus m_0$ (0 here means a vector filled with zeros) $H_1 = E(H_0,m_1) \oplus H_0 \oplus m_1$ where $E(K,M)$ is a block cipher (for ...
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### Is there a way to break this encryption?

I was wondering about making up a simple system to encrypt a file: ...
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### Can I build a secure tweakable block cipher from a normal one by adding key and tweak?

Let (E,D) be a secure block cipher. Consider the following tweakable block cipher: ...
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### Generating a cryptographically secure, many-time use, symmetric encryption key

I need to generate a 256 bit encryption key described by the adjectives in the title. Currently I intend to create the key using this RNG. Is this a secure manner of creating the key, given that it ...
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### Trying to find an algorithm to share portions of a key with multiple people

Sorry if this question's a bit basic, but I don't know of any way to ask it concisely enough for a search... What I'm looking for is a proven means of doing the following: Create x number of ...
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### Additive ElGamal cryptosystem using a finite field

I'm trying to implement a modified version of the ElGamal cryptosystem as specified by Cramer et al. in "A secure and optimally efficient multi-authority election scheme", which possesses additive ...
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### McEliece Cryptosystem Implementations

Are there any current implementations (language irrelevant) of the McEliece Cryptosystem? I have been hunting around all day, and yet, have only found a few mathematical equations pertaining to the ...
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### Recovering state of modified RC4 key scheduling algorithm

Consider this algorithm: ...
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### Can I jettison MAC if I already have SHA1(M)?

I'm currently using SSL with AES-CBC and HMAC for a file transfer containing string M. Now suppose Alice already knows SHA1(M) (and the adversary does not), and she downloads M from Bob using only ...
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### Is there a standard for OpenSSL-interoperable AES encryption?

Many AES-encrypted things (files, strings, database entries, etc.) start with "Salted__" ("U2FsdGVkX1" in base64). I hear it's some sort of OpenSSL interoperability thing a b c. Is there some ...
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### How does a birthday attack on a hashing algorithm work?

A "normal", brute-force attack on a cryptographic hashing algorithm $H$ should have a complexity of about $2^{n}$ for a hash algorithm with an output length of $n$ bits. That means it takes about ...
313 views

### Why is a MAC needed?

I agree that for certain encryption systems or modes of operation, a MAC is indispensible. The best example are probably stream ciphers (and therefore also block ciphers in OFB or CTR mode) that ...
531 views

### Deniability of OTR messaging

I've been looking at the off-the-record messaging protocol, and there is something about its deniability property that seems strange to me. Consider the following scenario: In the course of an ...