# All Questions

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### Questions about self-signed Certificates' Fingerprints and Client-Server Interaction through SSL [migrated]

I have some questions about how the fingerprint function is performed. First of all, I have some knowledge about cryptography. However it seems to do not be good enough to understand hundreds of ...
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### Are there any reasons for using SSL over IPSec? [migrated]

is it recommended to use both protocols together? In which situation?
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### Does bad IV generation weaken CBC? [duplicate]

Let's say that I generate an IV like so: dd if=/dev/urandom of=iv.bin bs=16 count=1 Let's also say that /dev/urandom has been ...
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### Can astronomical radio sources be used as a verifiable randomness beacon? [closed]

A randomness beacon is a source of random data that is broadcast to multiple parties. Users listening to the beacon receive the same sequence of random strings and no one can predict the values in ...
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### Is there any _true_ anonymous cryptocurrencies? [migrated]

I've been looking into Bitcoin recently and stumbled upon numerous notes how Bitcoin is not anonymous at all, or how it's only partially anonymous and you can easily trace your funds. So, this ...
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Alice pays Bob $5/month to host a gigantic file for her. She wants to occasionally verify that Bob is actually hosting the file. To do this, she selects random blocks from the file, and ... 0answers 86 views ### Convergent encryption has dictionary attack, but why hash function doesn't? Convergent encryption (CE),$E_k(d)$, is a way to encrypt the data$d$, with the characteristic that the encryption key$k$is$k=h(d)$, where$h(\cdot)$is a cryptographic hash function. Consider a ... 0answers 37 views ### OpenSSL: do I need multiple EVP_CIPHER_CTX structures? [migrated] This may need to be on StackOverflow instead. I have a single-threaded client/server application that needs to do both encryption and decryption of their network communication. I plan on using ... 1answer 72 views ### How does the Hashlet work? [on hold] DISCLAIMER: I don't know a lot about cryptography. I was reading about the Hashlet, and I had a couple questions. The Hashlet is described as: SHA256 hardware device with a hardware RNG, and ... 0answers 68 views ### RSA: Common modulus attack problem [duplicate] I understand in theory how the common modulus attack works (as described here: how to use common modulus attack?) Though, I did not understand completely how it worked with a negative$s_i$. Since ... 0answers 52 views ### What are the consequences of not checking the server mac in a TLS connection? The context for this question (it's quite involved) can be found in this document: https://docs.google.com/file/d/0B15itpMWb2ztWTJrYTgzX204OVU However, I want to make it clear that you don't have to ... 0answers 145 views ### Elliptic Curve based blind signature implementation I want to use Elliptic Curve based blind signature scheme for my research. There is no proper implementation of ECC-based blind signatures. Can someone describe to me which things I need to follow ... 0answers 47 views ### P = NP security implications [duplicate] If someone finds an efficient way (ridiculous or not) to turn NP into P (such as creating multiple universes, saving the one with the correct answer), would we have any good algorithms for encryption, ... 0answers 61 views ### AES/CBC fixed Initial vector use-case [duplicate] I am using AES/CBC to encrypt my http cookie. I never encrypt the same cookie value twice so my understanding is I don't need to use a random initial vector - using a fixed initial vector is fine for ... 0answers 69 views ### Can you determine an unknown value when it is combined with a known value and you are given the resulting hash? Say I have a string that I want to keep hidden. You can then enter a known string which is added to the end of the hidden string and you are given the sha256 hash of the combined string. If you were ... 1answer 109 views ### RSA, finding p,q [duplicate] If the public key$(e,n)$and the private key$(d,n)$are known, what is the easiest way to find the primes$p$and$q$? When$n$and$\phi(n)$are given this is easy to solve. But I can't manage it ... 0answers 68 views ### How to decrypt a text which is ciphered same length key? [duplicate] I have ten piece of ciphered texts. I know that they ciphered with a same-length key. Any idea how I can decrypt the ciphertexts? What kind of algorithms should I use? What are the points of taking ... 1answer 48 views ### Can N, q be shared for multiple users when using SRP-6A Is it considered bad practice to use the same N and q parameters for all users in an SRP-6A based authentication system? I know that q MUST be a Sophie Germain prime and N a safe prime, but can they ... 0answers 71 views ### Cryptodefense ransom use RSA-2048. Any chance with known plaintext attack? [duplicate] The "new" kind of ransomware invade your computer and crypt all your files using the RSA-2048. Personally, I have been victim of cryptodefense: 40000 files encrypted... I'm not going to pay anything ... 0answers 31 views ### Bit strength of combining hash functions? [duplicate] Suppose there are hash functions H1 and H2 with bit strength of H1 and H2 is n1 and n2. A new good hash function is generated by combining H1 and H2. What will be the bit strength of these combined ... 0answers 39 views ### Does RSA work properly with non prime factors? [duplicate] I know RSA should not use non prime factors for p and q for security reasons, but still, just out of curiosity, will RSA work 100% accurately i.e. message encrypted with one of the key produces same ... 1answer 46 views ### Block cipher encryption of decryption with the same key With block chipers can I assume that Enc(k,Dec(k,m))=m Meaning if I decrypt something with a key k and then encrypt the result with the same key k, do I get what ... 1answer 46 views ### From Factorisation of semiprimes to breaching confidentiality If someone or some group found an efficient way to factor large composites with two distinct prime divisors, would this make it easier to decode any messages? 0answers 17 views ### Vernam Cipher with Repeating Key [duplicate] I'm doing a piece of coursework for Uni and the task is to break a Vernam Cipher. So we have a randomly generated key which is as long as the message. It gets used for all the messages sent from that ... 0answers 47 views ### Tiger Tree Hash vs generic Merkle Tree Is there any advantage of using Tiger Tree Hash over any other hash function organized as the Merkle tree? Are there maybe any properties of TIGER that, say, SHA2 or BLAKE in Merkle tree do not have? ... 0answers 28 views ### What can I change in Lane to What can I change in Lane to increase memory (and compute) consumption. My first idea would be to change n, but with Lane hash function is there a way I can up the n to a level higher than 512. If I ... 0answers 110 views ### New modulus or new key pair? I have this assignment question that I'm not sure how to answer. Any insight would be helpful. In the RSA public-key encryption scheme, each user has a public key, e, and a private key, d. Suppose ... 0answers 51 views ### How to know private key is computed from specific partial private key? In a certificate-less cryptography, I have learned that – to resolve the key escrow problem of IBE – the concept of a partial private key is used. Now, consider the following Scenario: After ... 0answers 35 views ### Locally Dedcodable Codes and Private Information Retrieval Does anyone know about Locally Decodable Codes (LDCs)? It seems the private information retrieval schemes that based on LDCs are computationally efficent (answer a query without processing the whole ... 0answers 50 views ### Is timestamping possible without publishing? The Wikipedia article Trusted Timestamping states that we can timestamp data by publishing it's hash. Publishing can be done either independently or via a third-party publisher, as explained by ... 0answers 51 views ### Re-encryption mixnet Can an Elgamal-based re-encryption mechanism be used in a free route mixnet topology? Until 2006 it was not possible, but I couldn't find the later research results or achievements. Can anyone suggest ... 0answers 30 views ### Is it possible to weaken a bitcoin private key by 'using' it elsewhere? [duplicate] What are the increased possibilities (if any) of being able to crack a private key given the following: The associated bitcoin (ECDSA Secp256k1-based) public key is known. The private key has been ... 0answers 63 views ### How to make a crypto-currency robust to 51% attacks? For Example: In Bitcoin it is theoretically possible to double spend if you control > 50% of the computational power in the network. Also it is possible to apply "selfish mining" with far less than ... 0answers 77 views ### Any field in a PKI certificate where some text info can be stored? I want to store 5-10 lines of Text Info in a PKI Certificate. All I want is that when using common tools like openssl command line or certutil from Microsoft, this text info should be displayed as is. ... 0answers 92 views ### m ∈ Zn \Z*n, RSA works but not secure If you happen happen to have a message m ∈ Zn \ Z*n, RSA works but not secure. How likely is it going to happen? |n|=1024 bits |p| = 512 bits |q| = 512 bits. 0answers 36 views ### Encryption of numeric value using playfair I am studying in CSE and in my recent exam paper, A question was asked as: Construct a playfair cipher for Plaintext: semester5 and key:technology. Generally as we are taught yet, there is no ... 0answers 105 views ### Defending hybrid encryption schemes against padding oracle attacks I intend to use a generic integrated/hybrid encryption scheme for transmitting information between a client and a server. Key encapsulation: a 128-bit symmetric key is generated and asymmetrically ... 0answers 108 views ### Challenge–response authentication which can be done in head? Say we have door where you have to say a password to pass. If theres someone standing nearby he would hear the password and could also use it. So therefore the doorman gives you a different number ... 0answers 64 views ### Current standard security level for a hash function? What is the current level of security needed for a hash function? Until not long ago this was 80 bits. What about now? 0answers 63 views ### Problem implementing MixBytes functionality in Groestl Disclaimer: School work. I am trying to implement Groestl through Java, and have got stuck on the MixBytes section which can be found here section 3.4.5 page 11. As per the description of matrix ... 2answers 63 views ### counter to indicate hotp count I was trying to figure out how HOTP kept from wrapping over, when I saw this explanation of how it works, by Thomas Pornin [source]: The intended scenario is the following: the client has a ... 0answers 71 views ### Where can I download a database of RSA keys? I'm looking to do some research into how RSA is used in the wild. I've read through a few papers and it seems other researchers have had no trouble collecting millions of keys to perform analysis on. ... 0answers 77 views ### Weil pairing implementation - low level programming language I'm just started to studying elliptic curve cryptosystems. My one month-goal is to write a simple signature system based on the Weil-pairing. Some parts of it can be written without deeper ... 0answers 66 views ### IND-CPA Security Given a key$K$(the key is fixed) and a nonce$N$(changes from one message to another) Using a secure Key derivation function (KDF) such as the ANSI-X9.63-KDF with SHA-1 option to derive a key for ... 0answers 35 views ### Determine the iteration times using Pollard's rho Method for factoring Let's say, we have a large number$n=181937053$and$f(x)=x^2+1$. And also we know that$n=12391 \times 14683$. The problem is that ,using Pollard rho method, can we find the algorithm iteration ... 0answers 40 views ### Retrieve cryptographic key knowing cyphertext and plaintext [duplicate] I was curious about cryptography so I started to learn about symmetric encryption. From what I understand a symmetric encryption works as follow: PlainText -> (Encrypt)K -> Cipher text -> ... 1answer 233 views ### AES CBC Security I am building an Apache webserver with TLS 1.2 and OpenSSL 1.0.1. So far, I have enabled 2 encryption algorithms - ECDHE AES256 GCM and ECHDE AES128 GCM. Firefox and Chrome(ium) use NSS which ... 0answers 103 views ### How does converting character set affect hash entropy? Does mapping a large character-set hash onto a small character-set hash lower entropy for a fixed size substring? I'm writing a python app that involves generating passwords for websites. During the ... 0answers 46 views ### Private Set Intersection Polynomial Computation [duplicate] I am trying to implement the protocol mentioned in Section 3.4 of “Efficient Robust Private Set Intersection” in Java. In the Second Step, the Client computes a polynomial of degree$n$over the ... 0answers 55 views ### Plaintext patterns leaked based on single bit Assuming that Elgamal is used as an encryption cipher, where lets say$p$is 2048bit prime. Is it possible for an attacker to figure out$x\$, a secret key, if any part of 2048 bits ciphertext and ...

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