# All Questions

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### Individual bits of Textbook RSA

This question relates to the underlying RSA assumption. Forgetting about the fact that Textbook RSA is deterministic, I am curious about the assumed strength of the RSA problem. Does RSA hide all ...
138 views

### AES Key Length vs Block Length

This answer points out that certain key and block lengths were a requirement for the AES submissions: The candidate algorithm shall be capable of supporting key-block combinations with sizes of ...
91 views

### Can the encryption exponent e be greater than ϕ(N)?

So I was just wondering in RSA, can the encryption exponent e be greater than ϕ(N)?? For an examples sake, lets just say N = 707, so p = 101 & q = 7. So, we have ϕ(707) = 600. Can I have e = ...
62 views

### use the same pad reversed

lets say I have this random numbers ' 625 467 921 ' and use them once to encrypt a message otp style and then I want to use them again so I reverse them to be ' 129 764 526' and use to encrypt the ...
105 views

### A question regarding relevance of vulnerability of MD5 when linking multiple records together

I have been studying a Supreme Court case "IMS Health vs Sorrel". In this case a Friend of Court brief filled by "Electronic Privacy Information Center" states that use of MD5 hash function to link ...
198 views

### Why is h(m||k) insecure?

Here is the post that explains the failure for doing h(k||m) and I understand it. But I don't understand how h(m||k) is subjected to collison attack, or birthday attack. Please explain?
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### Good enough deterministic PRNG based on hashes

Lets say I have a seed named iv which has a decent amount of entropy. Are there any glaring issues with the following? First 64 bytes are generated by SHA512(iv) Next 64 bytes are generated by ...
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### phi(P*Q) = (P-1) * (Q-1)

I was trying to understand RSA when I encountered the Euler Function. I do understand this: $\phi(P)$, where $P$ is a prime is $P-1$. However it seems that for a number $N$ such at $N=P\cdot Q$ where ...
61 views

### Is there a big RSA Data Set

Is there a big dataset containing RSA public $(n,e)$ and private keys $d$ and primes $p,q$ where $n = p.q$ ?
139 views

### How to generate a random integer in interval $[1, 2^n-1]$ from random integer in interval $[0, 2^n-1]$?

For a project I am working on, I have access to a CSPRNG that outputs a random integer in the interval $[0, 2^n-1]$ for any integer $n$ greater than 0. I cannot use the zero values, so I have my RNG ...
308 views

### creating a small number from a cryptographically secure random string

i'm trying to figure out the best way to generate a cryptographically secure random number between 0 and 200 from a cryptographically random string of bytes (ie. read from /dev/urandom or some such) ...
150 views

### security of Felix cipher

I just find this pencil and paper cipher 'Felix' on this site and I want to know how secure it is?
151 views

### Did Merkle invent cryptographic hashing?

Chapter II of Merkle's 1979 PhD thesis is titled "One Way Hash Functions." The chapter appears to be the first reference to cryptographic hashing. The chapter has no references. Is there an earlier ...
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$N=p·q$ ($p$ and $q$ are prime numbers), $m_1, ..., m_x$ are the messages, $e$ and $d$ are RSA encryption and decryption exponents, respectively. I am given $e, m_1, m_1^e, m_1^d, ..., m_x, m_x^e, ... 3answers 255 views ### ANSI X9.31 standards for generating random numbers The NIST-Recommended Random Number Generator Based on ANSI X9.31 Appendix A.2.4 Using the 3-Key Triple DES and AES Algorithms has 3DES being used three times for each 64-bit block of random data ... 1answer 148 views ### Is there a field guide to ECC for the IT Security layman? I'm trying to understand ECC from an IT layman's perspective and am trying to separate the theory from the standards, and understand why certain features are implemented or not implemented in the ... 3answers 115 views ### Public keys and their protocols I'm having difficulties understanding exactly what this protocol means:$S \to D : \{N_S , S\}K_DD \to S : \{N_S , N_D \}K_SS \to D : \{N_D \}K_D$"where$S$represents the supervisor’s ... 1answer 186 views ### A single password manager vs password generator/hash I have been wondering about the options available for managing passwords. However, they all seem to fail if the master password is compromised (which isn't a big surprise). On one hand you have ... 2answers 112 views ### Probability that an attacker wins the discrete logarithm game when exponents are drawn from a subset Suppose$g$is a generator of an order$p$cyclic group in which discrete logarithm is hard and$p$is a prime (i.e., given$g^x$for a random$x \in \{0,1,\ldots, p-1\}$, it is hard to recover$x$... 2answers 186 views ### Is there any semantic difference between predicate encryption and functional encryption? Predicate encryption(PE) arrived as a descendant of attribute based encryption. Attribute based encryption allows the encryptor to embody a policy to the ciphertext (Ciphertext-Policy based ... 2answers 133 views ### Number of states in a LFSR Do all$2^{\ell}$(where$\ell$is the bit length of the shift register) states always occur in a LFSR or can I choose my taps badly so some states are skipped and the period is shortened? If so is ... 2answers 142 views ### Can one have an authentic, but repudiable, message without a previously shared secret? Bob wants to send a message to Alice, such that Alice can be sure that the message came from Bob, but can't prove it to anyone else. If I understand right, this means that the same message could have ... 2answers 90 views ### Polynomials and efficient computability In public key crypto, the popular definitions of security (CPA, CCA1,2) depend on PPT adversaries. I'm trying to understand why adversaries should be PPT. It's clear that adversaries should be at ... 1answer 146 views ### What are the benefits of lattice based cryptography? Previously we visited the benefits of elliptic curves for cryptography. Lattice based cryptography is starting to become quite popular in academia. The primary benefit of lattice based crypto is the ... 1answer 89 views ### Why doesn't this replay attack work on ECDSA? I've just started working with elliptic curves and ECSDA in particular, so my understanding of the underlying math isn't great. The thing I'm currently stuck on is trying to understand why replay ... 1answer 87 views ### S-box with differential uniformity = 2 I read that we do not know if there exists an 8x8 sbox with differential uniformity = 2. I suppose we cannot compute every possible sbox because there are$64!$possible s-boxes. Am I right? Is ... 0answers 61 views ### Differential Cryptanalysis of FEAL-4 I'm currently carrying out a differential attack on the FEAL-4 algorithm, however I have hit a bit of a wall. Basically I attacked the final round first (K3) using the differential characteristic of ... 1answer 142 views ### Can a shift cipher attain perfect secrecy? On a practice question for my intro cryptography exam, it asks the following: Assuming that keys are chosen with equal likelihood, the shift cipher provides: A) computational security ... 2answers 130 views ### Contruct a protocol to determine if three secret keys are different, without revealing any of them? I am trying to find a protocol for this problem: Three persons,$A$,$B$, and$C$, know secret numbers$s_{A}, s_{B}$, and$s_{C}$, respectively. They want to know whether their numbers are all ... 1answer 84 views ### Need for Twin Elgamal encryption What is the need for two private/public keys in twin elgamal? I'm relatively new and would need some help. 2answers 82 views ### What are the cryptographic assumptions in the Dolev Yao model? In the Dolev Yao model for interactive protocols, the cryptographic primitive (encryption, for example) is considered as a blackbox. Does blackbox here mean that the primitive is to be considered CPA ... 1answer 228 views ### How much extra information is in an RSA public key? I'm trying to calculate the size of an RSA public key in Ruby. I've retrieved the key in PEM format, and once I've decoded the base64 part from the PEM format, I get the size in bytes. What I find is ... 1answer 230 views ### RC4 encryption -> AES encryption = more or less secure than RC4 or AES alone? Say I have ... 1answer 433 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? 1answer 227 views ### Attacks on the RSA Cryptosystem I was reading some articles about attacks on RSA system and I wonder about some generalization of the following theorem. Theorem (Coppersmith). Let$N=pq$be an$n$-bit RSA modulus, where ... 3answers 131 views ### Can I use PGP to sign a message without providing cryptographic non-repudation? The difference between a digital signature and a MAC is non-repudiation. A message with a digital signature proves that only the sender could have signed the message, whereas a message with a MAC ... 3answers 361 views ### Why is OCB-AES mode not becoming a standard for authenticated encryption? The OCB mode of authenticated encryption (used for example with AES) is the fastest way to provide authenticity and confidentiality without having to strive into questions like: Encrypt then MAC, MAC ... 1answer 90 views ### inverse element in Paillier cryptosystem As I know, in Paillier cryptosystem, the encryption$c$of a message$m$is calculated as$c=g^m r^n \bmod n^2$. Now, I am wondering if I can derive$g^m \bmod n^2$given that I know$c$,$r$, and ... 2answers 289 views ### Deriving Keys for Symmetric Encryption and Authentication So here's the concept. Rather than storing 2 keys and using a random IV, which presents its own problems (key rotation, ensuring no key is used in more than 2^32 cycles, sharing the keys, etc), is it ... 1answer 106 views ### RSA Key generation Public exponent too big I'm currently writing a paper about RSA (a self-chosen subject). I'm writing about the key-generation in RSA, and I have problem finding the public exponent e. I have chosen p = 61 and q = 53. Then ... 2answers 189 views ### RSA blind signatures in practice Hi I have a problem with moving my blind signature implementation from educational (textbook RSA) to more practical (padded RSA) side. David Chaums paper gives a following figure:$r$- blinding ... 2answers 117 views ### Information leakage in real-time voice encryption I saw some time ago a post discussing the issues surrounding encryption of speech/voice in VoIP and how it can leak information (can't find it now). Can someone provide an insight into some of the ... 2answers 157 views ### Are really, really long passwords any securer than short ones? Just for fun, I want to encrypt a message that will take about 10 or so years to decrypt. My idea is to encrypt a message with AES-512 with a password one million decimal digits long. Knowing not ... 2answers 124 views ### Public key cryptography - public key encrypts and cannot decrypt? I understand the basics behind public key cryptography, in that each party has two keys - the public one encrypts, and the private one decrypts. What I cannot figure out is, How does the public key ... 2answers 498 views ### RSA 4096 bit key benchmark is there any benchmark for RSA 4096bit long keys on general computers ? how many encryption decryption possible per second ? all benchmarks only show 1024 and 2048 benchmarks :( 0answers 77 views ### Factorize RSA knowing several N and E I did a CRT challenge yesterday and theres one problem I was unable to solve, probably due to my lack of understanding advanced crypto math. Its about RSA. There are ten given pairs of N and E ... 1answer 112 views ### Diffie-Hellman is Post-quantum secured? If Alice and bob have a secure channel for key-exchange and mallory don't man-in-the-middle attack them but in the future eavesdrop connection and see the key exchanged, can mallory break it like RSA ... 1answer 133 views ### using Post-quantum asymmetric ciphers instead of RSA We can't trust RSA to encrypt our Emails so what is best post-quantum cryptography system as alternative for RSA which provide good security and don't be breakable? because McEliece cryptosystem looks ... 3answers 125 views ### Deterministic key generation In a situation where it is required to generate n number of keys deterministically from a single piece of seed information can we assume that b breached number of keys, no matter what the quantity ... 1answer 143 views ### Why are protocols often proven secure under the random oracle model instead of a hash assumption? Is this true that whenever you design a protocol using a hash function, you must prove its security under the random oracle? I mean, is it possible to devise a protocol$P$using a function$H\$, and ...

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