# All Questions

1answer
151 views

### What key length is required to keep simple keyed “hash” secure?

In a previous question, I described a particular keyed "hash" that mapped a 5-digit input code into a 5-digit output code. It used a 8-bit key which is very insecure - more than 99% of the time, you ...
1answer
573 views

### How random are commercial TRNGS

I'm thinking about buying a USB TRNG. How do I evaluate its randomness? I'm sure some are better than others but which is which? Are thermal-noise better than radio-noise TRNGs?
2answers
283 views

### Perfect Secrecy, two Definitions

I'm reading the proof of the implication "Def 2.1 $\Rightarrow$ Def 2.4" in these slides about Adversarial Indistinguishability and Perfectly-Secret Encryption. I have a doubt in the slide 10. Here it ...
1answer
149 views

### Is this algorithm secure?

I recently found this site, proposing a hashing algorithm for passwords. They describe the following: pad the password on both sides with SHA1(email) to ...
2answers
147 views

### Physical Level Encryption

What types of algorithms that are capable of signing a message are out there that run on a physical level, e.g. lacking the infrastructure of a standard PC, no memory, processor or motherboard in the ...
2answers
351 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 ...
1answer
608 views

### How to calculate cycles per byte [closed]

Sometimes, websites and scientific papers that introduce and/or handle cryptographic algorithms also provide speed-analysis and tables comparing the individual performance of cryptographic ...
2answers
415 views

### Why this k parameter is in unary in adversary PPT algorithm? [duplicate]

While reading some text on cryptography, I found that algorithm $A$, that the adversary (called Eve by convention) runs to break the cipher message, needs two parameters, candidate message ($y$) and ...
1answer
381 views

### Alternatives to HMAC + CBC?

I'm looking at using HMAC + CBC. The combination looks like this: ciphertext = AES256(text, k1) data = HMAC-SHA256(iv | ciphertext, k2) | iv | ciphertext Where: ...
2answers
1k views

### Is Base64(SHA1(GUID)) still unique like the original GUID?

Basically what the title is; GUIDs are unique by design. If you run the GUID through SHA1 and then Base64 the hash, will the resulting string have the same guaranteed uniqueness as the GUID, or not?
2answers
539 views

### What are the potential security impacts of using CRAM-MD5 for Emails, when not using an SSL connection?

Background: My current server-provider tells me it's no problem to store the passwords in plain-text in the database, saying he has to do so because they use CRAM-MD5 for email authentication. But ...
1answer
147 views

I'm taking an online class on cryptography at corsera.org / Stanford, and the professor is explaining that it's OK to truncate an AES MAC to $w$ bits as long as $1/2^w$ is still negligible (say $w ... 1answer 313 views ### Polynomial multiplication and division in2^128 I want to multiply and divide polynomials, and implement the extended Euclidean algorithm for polynomial greatest common divisors, over a Galois Field of size$2^{128}$. Moreover, I want to use the ... 1answer 556 views ### How does OAEP improve the security of RSA? The heart of OAEP algorithm used for RSA encryption are the cryptographic hash functions$H$and$G$. Does everybody (so also an adversary) know these functions? If YES: How does it help the ... 1answer 155 views ### Is this a sensible cryptographic protocol intending to reduce the impact of compromised security? I'm in the process of designing a cryptographic protocol which will reduce the impact an attacker will have if they gained root access to a server storing data. The basic crux of it is that keys ... 2answers 867 views ### Generate fixed length cipher text from arbitrary length plaintext Using an encryption algorithm like AES, is it possible to generate a fixed length cipher text no matter how long the plain text becomes? 1answer 569 views ### Hill-cipher, disordered alphabet I am going to apply a simple substitution cipher to my input, then encrypt the result with a Hill cipher. How can this be broken, in a chosen-plaintext threat model? In other words, instead of the ... 2answers 323 views ### Help me describe/identify this challenge-response protocol/algorithm? My area of expertise is reverse engineering, specifically embedded systems. I do attack cryptographic systems, but this largely involves key recovery or exploiting the implementation. I was asked to ... 2answers 198 views ### Is Functional Encryption about Access Control over encrypted data alone? Informally, In functional encryption system , a decryption key allows a user to learn a function of the encrypted data. But all i see is that the function acts as an access control over the data. ... 0answers 42 views ### calculating beta for elgamal elliptic curves [duplicate] Suppose we use elgamal elliptic curves for secure communication. Bob selects a prime$p$, an elliptic curve$E$, a point$\alpha$on$E \pmod p$, and a secret integer$f$. Suppose that Bob has ... 3answers 453 views ### SHA-1:Is there any mathematical result that gives us the minimum number of 1's in a 160-bit SHA-1 hash output? Is there any mathematical result that gives us the minimum number of 1's in a 160-bit SHA-1 hash output? What is the probability that a 160-bit SHA-1 hash output contains at least 128 1's? 2answers 1k views ### True random numbers generated by sensors Is using sensor raw data a good way of generating true random numbers? I mean using an IPhone's gyro/accelerometer raw output as a base for generating an array of true random numbers. 2answers 355 views ### Generating IV in TLS 1.2 I'm writing a TLS 1.2 implementation (in C#) using a custom protocol. My question is how to generate the IV attached to each message, I don't want to use RandonNumberGenerator because I've heard it ... 1answer 71 views ### PKCS#11: Which CKK_types are supported by CKM_PKCS5_PBKD2? On Solaris there's a function pkcs11_PasswdToKey() which is a wrapper of C_GenerateKey(). I made a simple test and it turned out ... 1answer 417 views ### What is a fair exchange scheme? The Wikipedia entry Fair exchange has only two lines, and the only paper I can find describing such a protocol is extremely complicated. Is this a new field in cryptology or can someone give an ... 1answer 80 views ### Encrypting a broadcast channel We're building a data service that is expected to go out through a single "fat pipe" channel. The design requirement says that the data in the channel must be protected by authentication and ... 1answer 1k views ### Using an MD5 hash as a password Suppose Alice is using a password prompt that only accepts up to 32 characters for any particular password. Memorization of long strings of random characters is not one of Alice's strengths, so she ... 2answers 386 views ### CSPRNG in JavaScript using Audio and Video I ported GnuPG to Javascript using Emscripten (not released yet). Now I need a good replacement for /dev/random//dev/urandom. ... 1answer 357 views ### Why is the discrete log problem easy when the exponent comes from a binomial distribution? I read in http://epubs.surrey.ac.uk/7219/2/esorics06.pdf that in exponential El Gamal the discrete log problem for recovering$m$from$g^m$can be made tractable when$m$is drawn from a binomial ... 2answers 333 views ### Why is the following RSA PRNG cryptographically secure? One requirement states that the generator has to withstand the next-bit test. Consider the following PRNG, where we calculate next output$x_i$via the formula$x_i = x_{i-1}^ e\mod n$. I can see ... 2answers 414 views ### Is there a way to do fair exchange between two parties who don't trust each other? Let's suppose we have an Alice who knows a secret key A, and Bob who knows key B. Using their own keys, they each encrypt a message (Alice encrypts$m_A$, Bob encrypts$m_B$) with their own key, and ... 1answer 314 views ### Designing a security system from scratch with a custom protocol, suggestions needed For the reasons I cannot go into details, I need to design my own protocol and overall security system which will be used to establish secure data exchange between various devices (most notably ... 2answers 709 views ### Combining LFSRs for Stream Ciphers: Why do we need high non-linearity? Linear Feedback Shift Registers (LFSRs) can be excellent (efficient, fast, and with good statistial properties) pseudo-random generators. Many stream ciphers are based on LFSRs and one of the possible ... 2answers 335 views ### How to do a literature search How do I do a literature search of the research literature on cryptography? Assume there's some topic in cryptography I'd like to learn more about; how do I search the cryptographic research ... 2answers 296 views ### Does SRP reduce to DH key exchange when shared password is not secret? I can find JavaScript implementations of SRP (Secure Remote Password protocol), but nothing that inspires confidence for Diffie-Hellmen key exchange. I also have a separate need for SRP later. I ... 4answers 790 views ### random number generator 10-side dice alternative A lot of sites (e.g. Dirk Rijmenants') refer to 10-side dice to generate random number for one-time-pad. I was thinking about new ways to generate random numbers, letters and passwords. here what I ... 1answer 321 views ### Is the DES algorithm in OPENSSL random? Look at the hex dumps of encrypted1.bin and encrypted2.bin . They both have same password A which was used to encrypt sampletext ... 2answers 369 views ### Finding hash almost-collisions A few months ago, XKCD posted a challenge to find a plaintext which hashed (using Skein 1024 1024) to a specified value. Inputs were scored based on the hamming distance between the hash of the ... 1answer 278 views ### Cryptography based upon neural networks [closed] I would like learn about use neural networks in cryptography. Is there any research literature on this subject? What should I do to learn about the subject? I am taking short course in neural ... 1answer 291 views ### Security of Salsa20 with some known plaintext? Basic question- if I'm encoding a bunch of known filetypes with salsa20, will it still be secure if the plaintext header is known? Assume that a different IV and Key are generated before each file is ... 1answer 484 views ### Trying to better understand the failure of the Index Calculus for ECDLP So I'm going to give you guys my understanding and then if you would be so kind as to tell me where I'm off the mark (hopefully I'm not completely wrong). So basically the index calculus for the ... 2answers 137 views ### Does knowledge of original file size provide a cryptographic weakness? I'm encrypting files using an AES-256 CBC cipher and an SHA-256 HMAC every 64KB in the file. Since AES CBC needs an amount of input bytes to be divisible by 16, I use PKCS#7 padding to bring the ... 3answers 387 views ### What kind of adversary is the cloud? I just started some work on computation over encrypted data in the cloud. We're still in the early planning stages, and to really understand the kind of security we can offer I need to determine what ... 1answer 1k views ### Winzip AES256 vs PGP If I use the AES256 option in Winzip to encrypt a file, is it any less safe or less secure than using pgp encryption? 1answer 623 views ### Recommended way of adding a pepper/secret key to password before hashing? There have been several questions regarding password hashing here and on Security.SE. A "pepper" is sometimes mentioned – an application-specific secret key. The canonical answer on password hashing ... 4answers 1k views ### Increased CRC collision probability when adding bits to input message The Scenario I have a message string I need to transport over a wireless network that may be unreliable. This message string is about 100 bits long, and is packaged with an 8-bit CRC. When the ... 1answer 224 views ### How to derive formulas for addition and multiplication in Jacobian coordinates Is there a way to derive the formulas for point addition and multiplication on elliptic curves in Jacobian format by yourself? How could I have derived these formulas by myself? 2answers 260 views ### Many consecutive hashes to slow down brute force attack? I've heard that hash algorithms like bcrypt are more secure because they take longer to complete, and therefore take much longer to prute force, without a noticable ... 1answer 181 views ### Weak One Way Function Show The function$mult(a,b)$is weak one way if the Integer Factorization Assumption is true. I am read the proof of this enunciated but I want know if I understand this in my way. The proof use the ... 1answer 355 views ### What does$(\mathbb{Z}_n^*)^2$mean? In a paper they write once,$(\mathbb{Z}_n^*)^2$. Is this the group of quadratic residues or is it something else? Here the theorem: Under the strong RSA assumption, given a modulus$n\$, along with ...

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