5
votes
2answers
238 views

Which crypto libraries/programs do we have the most confidence in? [closed]

I have recently begun studying crypto. If it's one thing I have learned it's that we should not implement our own crypto. Therefore we should look to using existing software and libraries. When I ...
1
vote
2answers
699 views

Custom crypto library in C

I will be making (in the near future) an app that will contain some pretty heavy crypto. As it is possible that my app will be ported to different devices (initially it will be iOs only, but Mac, ...
1
vote
1answer
125 views

With TLS and ECDHE, how does curve selection work?

Given that a TLS client and server have already agreed upon ECDHE for session key establishment, how does the selection of the actual elliptic curve ("domain parameters") being used for deriving the ...
6
votes
1answer
120 views

Cryptography used for login and signing transactions

My bank uses a smartcard reader (separate module not connected to the computer) as depicted below: When I need to log into my account it provides me with a challenge and I need to provide some ...
3
votes
3answers
293 views

Timing Attacks on ECDSA, ECDHE, AES and SHA2

Are there any known timing attacks (both practical and theoretical) on any implementations of the following? ECDSA (I'm aware of this one - are there any applicable to prime fields?), ECDHE (again, ...
2
votes
1answer
51 views

How do I know if a given curve requires a FpCurve F2mCurve or ECCCurve?

I'm trying to read a public key into Bouncy Castle (secp256k1) and need to choose from the following objects FpPoint; FpCurve; or ...
1
vote
1answer
727 views

HMAC SHA256 vs RSA SHA256 - which one to use

Salesforce recently announced they are moving away from HMAC SHA256 to RSA SHA256. Why did they make that move?. Any technical factors? Is HMAC really easy to break? ...
3
votes
2answers
196 views

Is there a companion algorithm for OTP to ensure integrity and/or authentication?

One-Time Padding is (theoretically) perfect encryption algorithm. Let's assume that these problems are solved: Fast generation of independent and identically distributed random variables Perfect key ...
4
votes
3answers
163 views

Why to try get key out of white box crypto? How can one protect WBC itself?

Help me understand the following. With WBC the question is mainly being stated as can one try to break WBC to identify the key. My question is: Why would one ever want to do that anyways? If one can ...
2
votes
2answers
178 views

Hypothetical unknown cipher - security in obscurity?

I'm curious what would happen in the following scenario: Suppose an attacker gets a hold of a cipher-text of sufficiently large length. And suppose he has the means to verify a successful decryption. ...
1
vote
1answer
49 views

How do you use the Tiger hash function with GPG?

I've searched Google and the GnuPG documentation and I haven't been able to find an answer. Some pointers in the right direction would be greatly appreciated.
0
votes
0answers
36 views

What is the default type of salt for encryptions in Heimdal Kerberos?

I am trying to figure out what the salting mechanisms are for various kinds of encryptions in Heimdal Kerberos. In section "4.11 Encryption types and salting" of the Heimdal Kerberos documentation it ...
11
votes
1answer
4k views

What are the differences between a digital signature, a MAC and a hash?

A message may be accompanied with a digital signature, a MAC or a message hash, as a proof of some kind. Which assurances does each primitive provide to the recipient? What kind of keys are needed?
1
vote
0answers
116 views

Security of .net AES implementation and security of a hash MAC

My question rather splits into two sections: Is AES correctly and security implemented in the .net Framework? Are there any reviews of implementation mistakes that would weaken the security of AES ...
3
votes
2answers
320 views

Why is sharing the seed and using SecureRandom “deterministically” so bad?

I've recently been reading an article about "using cryptography to store credentials", and I would love it someone explained this in more detail… Up until Android 4.1, Android used a SecureRandom ...
26
votes
6answers
3k views

Is there a secure cryptosystem that can be performed mentally?

I, myself, do not plan on getting into a situation where I would be unable to use a computer in order to communicate securely. However, I can think of many practical situations in which mental ...
1
vote
2answers
98 views

Is it possible to decide the base of a discrete logarithm?

Given $R$, a prime $p$ and two bases $g_1$ and $g_2$, is it possible to decide if $R = g_1^r$ mod $p$ or $R = g_2^r$ mod $p$ without knowing $r$?
1
vote
1answer
101 views

How do I prove that this PRNG is easily distinguished from a random sequence of numbers (modulo m)?

I was studying Crypto, and this question came up. Using a PRG like the multiplicative congruence generator: $b_{i+1} = a \cdot b_i \mod m$ How do I prove that the output of this PRG, or any PRG's ...
1
vote
1answer
929 views

Can AES use PKCS#5 padding

From What is the difference between PKCS#5 padding and PKCS#7 padding, I understand that PKCS#5 is defined for 8 byte block sizes. Does this rule it out as a padding option for AES since AES has a ...
1
vote
0answers
104 views

Can keys from Bitcoin's Hierarchical Deterministic Wallets be correlated (reducing privacy)?

I'm trying to understand if the feature "Hierarchical Deterministic Wallets" in Bitcoin allows for complete privacy of all derived keys, and if any of those keys can be associated with each other ...
1
vote
0answers
76 views

About repetitions of cipher alphabets in Cipher Text of play fair cipher [closed]

Can't we overcome the repeated cipher alphabets in Playfair generated cipher-text? Also, are the rules of the Playfair technique clear in all respects?
3
votes
2answers
138 views

Isn't the deterministic property of (EC)DSA a security problem?

From what I read in Wikipedia's article "Elliptic Curve DSA ~ Security", the "deterministic" generation of $k$ can help prevent certain type of attacks (such as the one happened to Sony). However, ...
2
votes
1answer
108 views

Good Encryption Exponent

I have placed a bet that I can create a public key such that my adversary will not be able to crack (decrypt) it for at least one week. For my primes $p$ and $q$, I chose very large numbers that are ...
6
votes
1answer
151 views

What's the state of the attack to get the first pre-image on MD4?

What's the state of the attack to get the first pre-image on MD4? Is it still $2^{102}$ as described by Gaëtan Leurent in "MD4 is Not One-Way" ?
2
votes
1answer
161 views

Can you help me understand how RC4-52 is done using pen-and-paper?

I've played a lot with VIC and enjoy its complexity and effectiveness as a field cipher. However, RC4 has caught my attention lately and I've read there is a RC4-52 variant that can be done by hand. ...
2
votes
1answer
565 views

Where can I find Secp256k1 ECDSA test vectors?

I`m currently implementing an ECDSA library based on curves like secp256k1. I would like to test it using some test vectors, like ...
4
votes
2answers
170 views

Can we proxy-re-encrypt using homomorphic encryption schemes?

Homomorphic encryption schemes are PKE schemes with an additional special method Evaluate. The Evaluate method takes input any function (as boolean circuit) and encrypted inputs of the function and ...
3
votes
1answer
363 views

What kind of multiparty computation is this?

The classic multiparty computation protocols are defined around " Untrusted parties trying to compute something together". But is there a cryptographic abstraction for, "Trusted parties trying to ...
3
votes
2answers
204 views

Are there any papers explaining how to port textbook RSA to realworld RSA?

Are there any papers, books, or link where it explains how the plain vanilla "textbook RSA" is actually implemented in practice with all the padding and stuff? Basically, I would like to know the ...
4
votes
1answer
99 views

What authentication techniques can be used by QKD Systems?

As it is well known that QKD systems are prone to simple MITM attacks… what authentication techniques are being used in QKD to prevent those attacks in practice?
3
votes
4answers
368 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 ...
4
votes
3answers
617 views

What is the likely cause the RSA algorithm gives back plain text in this case?

Text book question of Chapter 9 of "Crypto and Network Security" by William Stallings: When using the RSA Algorithm — if a small number of repeated encodings give back the plain text, what is the ...
1
vote
2answers
152 views

Can you distinguish encryption methods from the output?

Suppose that you see all IP communication packets between two computers for a day, as they pass through a connecting router, and this amounts to 10MB. You additionally know that all data transmission ...
9
votes
2answers
2k views

How can I calculate the SHA-256 “midstate”?

Recently I've been trying to implement some Bitcoin-related code, and I've stumbled upon a weird concept, a SHA-256 "midstate". Some explanation is given here. The general concept is that Bitcoin ...
2
votes
1answer
134 views

Is there a way to provide proof of batch RSA security?

Suppose we have two encrypted messages with two different public key issued from the one server. There is a client who wants to send these to messages to the server. In the middle there is an ...
3
votes
1answer
428 views

How can I generate a one-time password?

Through my reading about the generation of one-time password (OTP) I found that there are many algorithms that generate OTP and they are either based on time such as TOTP or based on mathematical ...
8
votes
3answers
250 views

Is there an algorithm to find the number of intersections of two sets?

Suppose both I and my friend have a set of integer numbers. We want to know the number of common elements in our two sets but without knowing elements of the sets of each other. So I don't want my ...
2
votes
2answers
490 views

Is there an effective way for public key generation in homomorphic encryption schemes?

Is there any way to effectively generate valid distributed public key in schemes like ElGamal or Benaloh for a number of participants? There's no need in private keys since there's no intent to ...
4
votes
3answers
400 views

How can I prevent a message replay with RSA?

I am using RSA to encrypt some data but I would like to eliminate the possibility of message replay. By message replay I mean sending a valid message multiple times to the original recipient. It is ...
2
votes
1answer
117 views

How to design a cryptographically secure file hosting service

How one would go about design something like Google Drive/Dropbox providing the following features: files are encrypted and decrypted on the client files can be synced between devices the service ...
4
votes
2answers
264 views

Using SHA3 as an entropy pool

Has any work been done on analyzing the SHA3 sponge construction for use as an entropy pool (e.g. /dev/random)? All the use cases I've heard of consts of a ...
1
vote
1answer
246 views

RSA decrypt long messages (javascript)

I am attempting to encrypty/decrypt a long message in RSA using javascript (with crypto-js and jsbn libraries). I posted this on stackoverflow too but I figured someone here on crypto might be able ...
1
vote
1answer
503 views

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 ...
4
votes
5answers
270 views

Would it be possible to generate the original data from a SHA-512 checksum?

So, I have a file that is XY Exabytes big. I create a SHA-512 hash from it. Are there any theoretical chances that I can retrieve the original data just from the sha512 hash? Also, are there any ...
0
votes
2answers
184 views

Open source implementations of Symmetric Searchable Encryption and Order Preserving Encryption

Are there open source implementations of SSE and OPE? Can anyone please point to sample codes, if available. EDIT If cryptDB is not an option, what other options are available? (Indeed, these ...
1
vote
1answer
257 views

garbled circuit vs fully homomorphic encryption

Consider an outsourced database to an untrusted cloud (think CryptDb), the question is how to compute a function $f(.)$ on the data. I think I understand how (fully or partially) homomorphic ...
3
votes
0answers
158 views

Logics for Cryptographic Information Games

Preamble: There is currently a zoo of various logics for evaluating (proving) security in cryptographic protocols. The idea is that, by expressing these protocols using some logic, you can create a ...
2
votes
1answer
129 views

Having 4096 bit keys and short (< 256 byte) messages, can I simply use the key as OTP?

Assumptions: Alice and Bob use (cryptographically secure, hardware-rng generated) 4096 bit keys. Each message is encrypted using a new key; meaning: once a key is used, it's destroyed. Alice and Bob ...
1
vote
2answers
270 views

Are there any hand ciphers not obsoleted by computer cryptanalysis? [duplicate]

Computerized cryptanalysis has obviously made formerly "secure" hand ciphers like Playfair, Four Square, and the Hill Cipher obsolete because they can be defeated in seconds. But is there a hand ...
0
votes
2answers
148 views

How is SSL secure from rogue Certificate Authorities?

There's one thing that I've never quite understood about SSL (which perhaps means I don't understand SSL at all): how is SSL secure from rogue Certificate Authorities? This is probably best ...

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