# Tagged Questions

Encryption is the process of transforming plaintext using a cipher into ciphertext to make it unreadable to anyone except those possessing the key. Decryption is the process of transforming that ciphertext back into plaintext, using the key.

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### Number of keys for a monoalphabetic cipher

My teacher stated that… The number of possible keys (E) in a monoalphabetic cipher is $26$! My thinking: Every letter in the alphabet can be $25$ different letters hence it the number of ...
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In Fully Homomorphic Encryption scheme represented here Fully Homomorphic Encryption over the Integers In the Evaluate process (see section “3.1 The Construction” of the paper): $$Evaluate(pk, C, c1, ... 2answers 145 views ### Correct way to read a given permutation cipher? In some literature I am reading – where they are explaining the permutation cipher – they have two examples, which encrypt a small block of text. But they seem to contradict each other: First ... 1answer 3k views ### Why is Triple DES not vulnerable to meet in the middle attacks? Consider the Triple DES encryption calculated as:$$C= E_{K_1}(D_{K_2}(E_{K_1}(P))).$$For a chosen plaintext attack, given plaintext P, we compute the result of D_{K_2}(E_{K_1}(P)) and store ... 2answers 2k views ### FIPS 140-2 compliant algorithms in Enhanced RSA and AES Cryptographic Provider (Windows XP) [closed] We have a native C++ application that supports Windows XP SP3. Recently we've decided to change our crypto algorithms to FIPS 140-2 compliant ones. We are planning to use the following algorithms in ... 2answers 5k views ### AES Algorithm processing time in Arduino vs Raspberry Pi The Arduino employs an 8-bit ATmega series microcontroller whereas the Raspberry Pi is based around a 32-bit ARM processor, and the Arduino is typically clocked at between 8-16MHz and with 2-8kB of ... 1answer 2k views ### Implementing OpenSSL padding I'm conducting an experiment dealing with differences in padding across different aes operations for my Intro to Crypto class, and the question says OpenSSL uses PKCS5 padding, and that I need to ... 1answer 112 views ### Is there a developer's resource that ties encryption methods and strengths to the appropriate usage scenarios? I'm not looking necessarily for implementations in any language (although it would help to list those resources as well), but what I am most interested in is a discussion of what advantages and ... 1answer 1k views ### Why is it a security problem that two RSA moduli are not co-prime? I found this security problem, for example: Alice has an RSA public key: e = 37 and \phi (totient, N_A = (pa-1)(qa-1)) is 55, so the key is (37, 55). Bob has an RSA public key: e = 37 ... 1answer 985 views ### What's the difference between Trapdoor Functions and Encryption Functions? From Wikipedia: A trapdoor function is a function that is easy to compute in one direction, yet believed to be difficult to compute in the opposite direction (finding its inverse) without ... 1answer 498 views ### Key Scheduling of International Data Encryption Algorithm (IDEA) How to perform the key scheduling in International Data Encryption Algorithm (IDEA), I took a research but I can't understand how to perform it, "further groups of eight keys are created by rotating ... 1answer 2k views ### Traditional DES scheme in Unix crypt function In a security context course, we need to reproduce the old DES hashing scheme in the crypt program, on an old unix system. I am actually reading the crypt page on wikipedia: The traditional ... 1answer 534 views ### How do I calculate the maximum plain text length allowable for a certain cipher text length? I am encrypting and storing sensitive values in the database. I have a set max length in the database, but in order to provide useful user feedback, I'd like to know the max input I should allow for a ... 3answers 239 views ### Looking for cipher that uses one ciphertext I'm new to Cryptography so please free to edit my question for clarity and add the appropriate tag. I'm trying to research if the following is possible. Suppose John has a message that he ... 2answers 839 views ### What is the time complexity of the RC4 encryption & decryption algorithms? I'm trying to figure out what the time complexity of RC4 encryption & decryption algorithms is, in big-O-notation. 2answers 1k views ### Can md5 be used for encrypting data? I know that md5 shouldn't be used for password hashing because of collisions and possibility of making dictionary attacks e.g. using rainbow tables. But what about ... 1answer 44 views ### Tackling encryption problems with “Zipf's law”? I am new to cryptography and was wondering if it would be possible to semi-reliably "decrypt" an encrypted message by using the statistical distribution of symbols (/letters/numbers) in the encrypted ... 1answer 62 views ### What are the possible security issues when exporting a plaintext database to a file like this? Say I have plaintext database with key-value pairs of usernames and passwords. Then I iterate through the database, encrypt the passwords, and write the username and encrypted password pairs to file ... 3answers 116 views ### Is all of encryption based on xor? For a long time I've been under the impression that all of encryption uses xor at its basic level. Is this true? What other method could be used to encrypt plaintext with a key? Asymmetrically, as ... 1answer 45 views ### XOR or add in one time pads? [duplicate] Is there any difference in adding the plain text and key vs using xor instead(apart from the performance improvements)? 1answer 109 views ### Is super encryption (aka “multiple encryption”) always good? I'm trying to use super encryption (also known as “multiple encryption”) with AES in CFB mode with IV and password salting and AES in CTR mode both without padding. I first use AES CFB and then AES in ... 3answers 137 views ### Adding dummy bytes to ciphertext I was wondering if interleaving the resulting crypted data with dummy bytes placed at random positions but known in advance by the peers could improve security (no matter the algorithm and strength ... 2answers 201 views ### FIPS 140-2 Compliance Testing Is there any tool which can be used to test that implementations follow FIPS 140-2 Compliance ? 1answer 159 views ### Implement AES with 16 bit block size? Can we implement AES with 16 bit block size ?if so what are its advantages and disadvantages?Is there any rule AES has to be implemented with 128,192,256 ?Can we use AES for odd number of ... 1answer 98 views ### have a question in the book “introduction to modern cryptography” "introduction to modern cryptography. 2ed" in page 254 "By obtaining sufficiently many estimates and letting x_{i} be the majority value, A{'}can ensure that x_{i} is equal to gl(x, e^{i}) ... 4answers 129 views ### How is an epsilon of 1/1000 non-negligible? Lately I've been studying cryptography and in the current course I'm taking we're reviewing statistical tests and how they can be used to determine if a pseudo-random generator is secure or not. ... 1answer 288 views ### How to encypt/decrypt messages after ECDH key agreement I am using Diffie-Helman key exchange to generate the shared secret. But how will can a message be encrypted using this shared key? 2answers 3k views ### How can a cryptosystem be unconditionally secure? The definition of an unconditionally secure cryptosystem states that the cryptosystem cannot be broken even with infinitely computational ressources and time. However, since most books define the ... 3answers 125 views ### How a file is encrypted? I thought encryption algorithms(like AES) are used to encrypt texts,so how a file or folder(containing pictures,videos,...) is encrypted?What is encrypted exactly? 2answers 138 views ### Are password salts equivalent to keystream? I was reading up on keystream when I came upon the definition of it: A keystream is a stream of random or pseudorandom characters that are combined with a plaintext message to produce an encrypted ... 1answer 149 views ### Is it insecure to encrypt the wrong plaintext? Most plaintext must be fed as a string or a binary object to be encrypted. However, it's often possible to mis-decode the plaintext before encrypting it. i.e. If it's received as a string in JSON, ... 1answer 281 views ### Combining Random Hashes - avoiding collisions and ensuring randomness I have a series of integers which I want to convert to random integer (64 bit). The idea here is to produce random numbers very quickly. The issues that good quality random numbers are required with a ... 1answer 229 views ### The relationship between the key length and encrypt time in Xor algorithm? I did work on the encryption algorithm and the decryption using the XOR method noticed that when more the key length, the less time spent on encryption and decryption. I have two questions in ... 1answer 113 views ### Prefixing data before encryption for passphrase confirmation? I'm encrypting data with AES, using CryptoJS. CryptoJS returns an empty string in case the data couldn't be encrypted with the given passphrase. I'm not sure if this is intended, or happens in all ... 1answer 115 views ### Is it possible to encrypt data in such a way that it cannot be decrypted with the key used to encrypt it but can be decrypted with another key I'm very new to cryptography and encryption so I apologize if the answer to this is well known, but I can't find anything in my research. The crux of the problem is the need to store data on an ... 1answer 239 views ### How do we arrive to the equation for solving D in RSA? We have been shown that DE is congruent to 1 mod phi(n). How do we arrive to the real equation for figuring out d that is d = e^-1 mod phi(n). I want to know the entire process. I am just curious, ... 2answers 171 views ### Encoding multiple fields with same AES key and vector? I'd like some advice on cryptography best practices. I need to store on my web app the users' credentials (login & password) for 3rd-party sites. I'm using AES-256 with random key and ... 1answer 190 views ### Public Key encryption /Assymetric encryption For a start, I 've got a question regarding the Public key encryption. I know the public key encryption overcomes the Key distribution issue with the symmetric encryption and that in the case of ... 1answer 1k views ### Is the salt value a secret or can it be stored in cleartext just like the IV? [duplicate] From Wikipedia I read that the IV is used to randomise the mapping of cleartext to cipher text and that the IV is usually stored (in cleartext) together with the encrypted record. ... 1answer 264 views ### Brute force attack on RSA - success criteria? In a hypothetical discussion we ended up with a concrete question I'd like to find the answer to: If you try to brute force an RSA encryption, but the original vale which was encrypted was just ... 1answer 253 views ### Indistinguishability attack example I want solve the next exercise. The author defined the experiment for the cryptosystem \Pi, the adversary A and the security parameter n as follows \mathsf{PRIV_{EAV}}(\Pi,A,n) The ... 1answer 137 views ### Needing to encrypt plain sight information Okay here are my requirements. I need a solution that can do the following. Lets say I have an encrypted piece of text with the value "20". and I have UserA and UserB I give UserA the Keys (/5 and ... 5answers 2k views ### How easily could this be cracked? I'm looking into encrypting files like this: First, I SHA-1 hash the password. Let's say the password is something normal like "hello123", and then hashed. Then I encrypt a file using this: ... 2answers 177 views ### Encryption algorithm which produces comparable results for substrings I am wondering is there any encryption algorithm available which produces comparable string. I am expecting the output as shown below. ... 1answer 4k views ### Removing Padded Value in Decrypted Message How to remove padded value in Decrypted Message? I am using AES Algorithm. Let's take this as the decrypted message: "abcdefghijklmn " There is a 2 space in ... 2answers 351 views ### Brute force a ciphered message? [closed] I wrote my own cipher to encrypt messages. I would like to test a sample ciphered message to see how strong it is. Are there any tools for such task either in Windows or Linux ? 2answers 346 views ### One-way function and factoring I am confused about the hardness of the one-way function behind cryptography -- if someone could factor the large number produced back into two primes quickly then the one-way function would be ... 1answer 358 views ### Verifying the integrity of ciphertext using the cleartext hash? I want to be able to verify the integrity of a ciphertext by providing the cleartext hash, for this to work it would need to:$$hash(crypt(cleartext)) = f(hash(cleartext)) Where $f$ is an ...
I've been reading about WhatsApp getting "end-to-end" encryption, and when reading about it, I've notice something. If I want to send a message from cell $A$ to cell $B$, since there's a public key, ...