# All Questions

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### Are there any advantages in using proprietary encryption?

Proprietary software generally relies on the fact that in keeping the encryption algorithm private, it gets an extra layer of security implying "Security through Obscurity." Obviously this phrase has ...
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### Insecure third party connection

My organization processes some PII data and shares it with an outbound connection (outflow only) that is a third party. The data transfer transactions occur without human intervention. That outbound ...
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### How does this affine cipher work?

I have a question about how I need to solve the following: A sentence has been changed to ASCII and then encrypted with the formula $E(x) = ax + b \bmod 256256$. All I know is that the first 4 ...
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### Key Distribution Center Key Protocol Analysis

As shown in the image, why is Circle 1 to be B and Circle 2 to be A? Why is not the opposite, that is, Circle 1 to be A and Circle 2 to be B? like this picture From my understanding, Notation B ...
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### How to find the keyword of the Playfair text knowing/not knowing the plaintext and having decrypted text?

I know how the Playfair cipher works. I would like to know how can I find the keyword of the play fair cipher in two cases: 1) knowing the plaintext 2) not knowing the plaintext? Some examples: ...
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Let : $G_{0}$ and $G_{1}$ be two multiplicative cyclic groups of prime order $p$, $g$ be a generator of $G_{0}$ and $e$ be a bilinear map, $e : G_0 \times G_0 → G_1$ and let $𝐶_{1} = ... 0answers 14 views ### Show that ECB,CBC,CFB,OFB,CTR are/aren't CCA-secure? [on hold] I've been looking for some materials that show why the common block cipher modes are/are not CCA secure. Unluckily, didn't seem like I could find anything. Any resources I could look at? Thank you. 0answers 33 views ### Numeric base conversion in cryptosystems? I have been wondering if numeric base conversion has ever found an application in cryptography. By base conversion, an example that is probably familiar is Base64 encoding. This is an example of ... 1answer 17 views ### Where in FIPS document stated that SHA-1 is not secured? SHA-1 is not secured for a very long time, but I still can see it here: http://csrc.nist.gov/publications/fips/fips140-2/fips1402annexa.pdf Where in FIPS document stated that SHA-1 is not secured? 0answers 8 views ### Background study to understand homomorphic techniques [on hold] I posted this question in academic stack but do not get answer so I am posting here as it is more relevant here. I am doing masters in information security. I am planning to do PHD. Homomorphic ... 1answer 33 views ### Factorization of RSA modulus using a qubic residue Suppose that someone uses RSA with$n = pq$, exponent$3$, also$3$divides$\varphi(n) = (p-1)(q-1)$and$2$different roots$y$and$z$of the equation: $$x \equiv c \ (mod \ n)$$ are known (for ... 2answers 233 views ### Does AAD make GCM encryption more secure? Does AAD make AES GCM encryption more secure? What if we drop AAD in AES-GCM 256? If we drop it, how will it make the encryption less secure? 0answers 28 views ### Message length for aes 256 in ctr, ecb and cbc mode I want to encrypt a message that have values between 0 and 50. So message have maxim 1 byte. Is possible to encrypt with aes256 in ctr, ecb and cbc mode, messages from 1 byte, not necessary 32 bytes? ... 1answer 19 views ### Am I correctly understanding TLS 1.2 PRF (Pseudorandom Function)? According to RFC 5246 Section 5 PRF(secret, label, seed) = P_<hash>(secret, label + seed) and ... 1answer 215 views ### CoAP authentication using DTLS what is the meaning of this notation ?? AES{Yi, (Yi XOR Ki | nonce1)} https://tools.ietf.org/html/draft-bhattacharyya-core-coap-lite-auth-00 1answer 50 views ### Is this a better involution S-Box for the Anubis cipher? After swapping random indexes of trivial involution$S[x] = ¬x$, I found the following involution S-Box with a non-linearity of$98$and a differential uniformity of$6$. Is there an upper limit to ... 1answer 89 views ### Rule 30 Cellular Automaton for Cryptography Steven Wolfram of Mathematica uses a pseudorandom number generator based on Rule 30 for applications in Mathematica software but I would like to know if a pseudorandom generator based on Rule 30 is ... 2answers 164 views ### Is there a way to optimize a linear scan while preserving anonymity? I've been wrestling with a problem, and I was hoping if someone else had a bright idea. Here's the problem: I have two sides, Alice and Bob. Alice has a single high entropy string$A$, and Bob has a ... 1answer 510 views ### Four-Square cipher and its keyspace Am I thinking about this correctly? Consider that the keyspace of the Playfair cipher is equivalent to all permutations of the alphabet, e.g. the number of distinct permutations of 25 objects, and ... 2answers 1k views ### How does cryptanalysis of the Playfair cipher work? I have a set of Playfair-enciphered data that I'm trying to crack without the key. I know I need to analyse bigrams; I've currently worked out what decrypts to th, ... 1answer 94 views ### Default algorithm for scalar multiplication of elliptic curve points by the MIRACL Library What is the default algorithm used by the MIRACL-Library [1] for elliptic curve cryptography systems to perform scalar-point multiplication with curves of Weierstrass form satisfying the equation : ... 1answer 21 views ### First preimage resistance check So I have$H: \{0,1\}^* \rightarrow\{0,1\}^n$a hash function resistant to the second preimage and to collisions. Let there be a function$H' : \{0,1\}^* \rightarrow \{0,1\}^{n+1}$with the following ... 0answers 13 views ### need help about X509v3 self-signing [on hold] I want to use Webhook feature of Telegram. However, I'm zero in cryptography and though I searched many times over the Internet, there were no good references which could help understand basics which ... 1answer 50 views ### Why is it that most messages seem to be expanded? Whenever I have seen a more secure version of a message, the message seems to be expanded by some factor. One example is RSA encryption, but whenever a message does not appear to be expanded it is ... 1answer 23 views ### Why Rabin fingerprints assumes data is prefixed with a “1” bit? (I know that a Rabin fingerprint is not a cryptographic hash, sorry in advance if my question is considered out of topic) In the paper Some applications of Rabin's fingerprinting method, it is ... 0answers 26 views ### DES Encryption Implementation [on hold] My program allows for the key and plaintext input to only be in numbers. However, I also need it to work when the input is in letters. For example the first input should be 0000000000000000 for both ... 0answers 19 views ### How feasible is a preimage attack or speedups to brute force a substring of MD5? Beyond the birthday problem analysis how feasible is a preimage attack or speed up brute force on a substring of MD5. For instance let's say from the 128 bits I decide to strip 24 bits, the first four ... 1answer 70 views ### Ciphers providing Deniable encryption? I stumbled on the concept of Deniable encryption on Wikipedia, with the following scenario: Deniable encryption allows the sender of an encrypted message to deny sending that message. This ... 1answer 55 views ### Combining secure hashes with insecure hashes? Assuming I'm a bank which seeks for secure hash functions to use in the process of signing on digital contents. I'd like to explain / prove why using each one of the following hash functions might ... 0answers 4 views ### Meeting people interested in Crypto and Programing [migrated] I have done some basic Micro controller programming in the past. I am now just starting to learn C++ and plan to move into Java and SQL eventually. I just got done reading one of Simmons books. It was ... 2answers 421 views ### About the Rijndael/AES sbox polynomial (subBytes) I've recently read a question about the irreducible polynomial behind the subBytes() operation in the Rijndael that has awakened and old curiosity I have: Why$\,m(x)$was chosen as ... 1answer 544 views ### Qubit / Qutrit - Is there a theoretical limit on how many orthogonal states a quantum bit has? Seems like a quantum bit with$3$orthogonal quantum states is called a qutrit - and they have been demonstrated practically. In comparison with$n$qubits that have ~$2^{n}$states, these have ... 1answer 26 views ### Why does OpenPGP encryption produce different ciphertexts from the same plain text? With the same plain text to be encrypted and the same public key, OpenPGP tends to produce a different ciphertext every time I run the encryption operation. Why is this? 4answers 3k views ### Why is plain-hash-then-encrypt not a secure MAC? It seems that even in MAC-then-encrypt systems like SSL, something like HMAC is used rather than a plain hash. Why? Suppose we use some stream cipher; then why can't we use$Encrypt(m | H(m))$as ... 1answer 51 views ### Is predictable ciphertext/plaintext bad? I have a cryptosystem that I'm using for secure chat. It is using AES 256 (with RSA 2048 for key exchange). Would a predictable, and repetitively sent ciphertext plaintext compromise the ... 1answer 29 views ### Is there a difference between$\mathbb{Z}_2^b$,$\text{GF}(2^b)$and$\text{GF}(2)^b$? I have read a lot about Galois Fields (GF). They are also presented in The Design of Rinjdael on page 13. In computer memory, the polynomials in$F[x]|_l$with$F$a finite field can be stored ... 2answers 120 views ### In the Quadratic Sieve, why restrict the factor base? In the Quadratic Sieve, when factoring a number$N$, many descriptions and most implementations select as the factor base the set of small primes$p_j$less than some bound$B$restricted to having ... 2answers 419 views ### What is the difference between chosen-plaintext attack and adaptive-chosen-plaintext attack? I've just dived in cryptography and would like to learn basics of this science. Currently I can't understand the difference between these two types of attacks. As I understood from Bruce Schneier's ... 1answer 23 views ### Security Strength of Double Substitution Ciphers I am wondering why people are using RSA keys when some types of double substitution ciphers seem to be just as secure if not better off. By some types of double substitution ciphers I mean one Which ... 1answer 29 views ### Different kind of PGP keys or IDs, how to interpret them? When people say "Here's my PGP key", they tend to come up with all sorts of different stuff. Sometimes they provide an 8-digit hexadecimal number, which seems to be a key ID (although I'm not sure). ... 2answers 327 views ### Perfectly secure shift cipher Prove that if only one character is encrypted using a shift cipher, then the shift cipher is perfectly secure. I want to show that$P(P=p | C=c)=P(P=p)$. But I don't know how to relate. Can anyone ... 0answers 30 views ### hash function for elliptic curve co-ordinates Is there any hash function which takes the co-ordinates of an elliptic curve$E_p(a,b)$as input and gives an integer value i.e.$h(.) : \{(x,y) \in E_p(a,b)\} \rightarrow \mathbb{Z}$1answer 901 views ### how to prove our algorithm is secure against chosen plaintext attack? I am working on a topic in cryptography where I have tried to develop an encryption scheme. How could I prove mathematically that my algorithm is secure against chosen plaintext attacks?. Will it ... 1answer 34 views ### Can you decrypt with 1 round key? If one has the last round key in an SP or Feistel network (the 16th round key in DES for example), would that someone be able to decrypt the rest of the encryption? 1answer 23 views ### El Gamal existential forgery using Pointcheval–Stern signature algorithm I found that there exists an algorithm that claims to make the El Gamal signature generation more secure. The algorithm can be found here as a pdf. I'm mainly interested in the two-parameter forgery ... 1answer 51 views ### SIV - Synthetic IV - S2V Construction? Benefits over a MAC or Hash? Looking at the SIV construction in rfc-5297 - https://tools.ietf.org/html/rfc5297 With regards to the generation of the SIV, using S2V construction, I am struggling to find the benefits of the chosen ... 1answer 30 views ### Number of Sbox in a Cipher Camellia has 4 SBOX and so does the TwoFish(key dependent 4 Sboxes). Where as AES uses only one. Would it have made AES more secure if AES had 4 or more SBOX too? Does using more Sbox with similar ... 1answer 325 views ### Where is the authentication tag stored in file encrypted using AES-GCM? So I am using cryptopp to encrypt a file in a project and I am using AES-GCM. I have a 256bit key and a 128bit ivec and a 128bit tag that I use to encrypt files. However, I want to know where the ... 1answer 188 views ### Rijndael S-boxes: Where do the$\mu$and$\nu\$ polynomial ring elements come from?

I've asked some other questions before about Rijndael's S-boxes, and step by step I'm coming to an understanding; but those steps often guide me to new questions. I did some lines of code to ...