# Tagged Questions

usually secret information used as input to various kinds of cryptographic algorithms, like encryption, signature, MAC, to select the concrete transformation done by the algorithm.

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### What is the main difference between a key, an IV and a nonce?

What are the main differences between a nonce, a key and an IV? Without any doubt the key should be kept secret. But what about the nonce and the IV? What's the main difference between them and their ...
7k views

### How can SSL secure a two-way communication with only one key-pair?

As I understand it, SSL involved the use of a public-private key pair. How does this enable two-way communication? Suppose I have some server with which I wish to communicate securely. I connect to ...
The definition of PBKDF2 states that I obtain a derived key (1) by calling a pseudorandom function a bunch of times recursively: $U_1 = PRF(password, salt)$ $U_2 = PRF(password, U_1)$ … $U_n ... 1answer 5k views ### Why do all SSH-RSA Keys begin with “AAAAB3NzaC1yc”? My Friend and I have been generating a few ssh2-rsa keys and noticed that all the public keys began with "AAAAB3NzaC1yc". The similarity extended to "AAAAB3NzaC1yc2EAAAABIwAAAQEA" between two keys I ... 3answers 692 views ### Where do I securely store the key for a system where the source is visible? I have a customer with an Access database (ugh!) in which credit cards are stored in plaintext (yikes!), so amongst other changes I'm doing in the app, I'm applying some encryption in there. I've ... 2answers 1k views ### When using Curve25519, why does the private key always have a fixed bit at 2^254? When using Curve25519, the private key always seems to have a fixed bit set at position 2^254. Why is that? Is there any good reason to use a fixed positioned most-significant-bit in the private key? 2answers 3k views ### How many RSA keys before a collision? I was wondering how many possible private/public keys exist? If a million people – for whatever reason – would try to generate 5 keys each in the same minute (on the same date and time) is there a ... 3answers 691 views ### Can we ensure the security of a crypto-algorithm and -implementaton against acoustic cryptanalysis? Like people always say: “Attacks only get worse…” — which is why I'm asking early. I have been reading the paper “RSA Key Extraction via Low-Bandwidth Acoustic Cryptanalysis” published December 18, ... 1answer 2k views ### Related-key attacks on AES According to Wikipedia: Related-key attacks can break AES-192 and AES-256 with complexities$2^{176}$and$2^{99.5}$, respectively. What are the requirements for these attacks (i.e how many ... 2answers 1k views ### How exactly does key whitening manage to increase security? Wikipedia states that key whitening increases security: In cryptography, key whitening is a technique intended to increase the security of an iterated block cipher. It consists of steps that ... 2answers 83 views ### Do I need to worry about timing attacks in Base64 encoding/decoding of private keys? Do I need to worry about timing attacks in Base64 encoding/decoding of private keys? This is a common operation (ex. PEM keys) and is variable time in typical implementations. 5answers 1k views ### Encrypt a file once with 50 characters password or twice with 25 characters? What better Encrypt the file once with 50 characters password or encrypt it twice each time with 25 characters password. 4answers 2k views ### What is the largest performed/possible bruteforce attack to date? I've read that cracking 128-bit key is currently out of reach of all humanity. However, I can't seem to find any information on what scope of brute force attacks have been performed or are possible at ... 2answers 3k views ### Using the same RSA keypair to sign and encrypt The RSA signature operation is basically the same as encrypting with the private key. In particular, both operations use the same kind of keys. Is it safe to use the same RSA keypair both for ... 3answers 4k views ### How and why can a decryption program tell me that a key is incorrect? I have noticed that some programs used for file encryption will tell you if an entered key is wrong when you try to decrypt. It seems (to me at least) that this would mean that the key somehow is ... 2answers 4k views ### How to calculate an IV when I have a shared private key? I'm working with a server/client system that has securely negotiated a private key. I need to encrypt/decrypt messages passing in both directions which are typically between 100 bytes to 100 KB. I'm ... 3answers 354 views ### How to protect key in software I need to encrypt/decrypt data from my software by AES, the problem is how to make the AES key secure, there is no HSM, should I hard code the key in my code? It seems that a hacker can read the key ... 1answer 1k views ### How does GPG verify succesful decryption? How does GPG (or other programs using the OpenPGP file format) verify that it has succeeded with decryption (for symmetrically encrypted data)? Is something appended to the clear text so there exist ... 2answers 826 views ### Is it secure to derive an AES key from a MAC? I'm working on a project where we need to encrypt a large number of files and store them on the cloud. And I'm wondering if the following process would be secure (we have a “Hardware Security Module” ... 3answers 12k views ### The modulus of RSA public key I am studying the RSA cryptosystem. The public key consists of$(n, e)$, the modulus (product of two large primes), and the encryption exponent. I want to separate the modulus$n$and exponent$e$. A ... 2answers 732 views ### Key Length & Hashing I need to use a hash function to generate a 128-bit key for a symmetric cipher. The specific cipher is from the eStream portofolio, called Rabbit. I am using the SRP protocol for authentication (a ... 1answer 2k views ### Is a private RSA key vulnerable to a chosen plaintext encrypted with that private key? I grasp that having known plaintext encrypted with the public key doesn't provide a means of discovering the private key (that being the whole point...). But if one were in a situation where they ... 3answers 812 views ### Order of cascaded ciphers Does the order of a block cipher cascade (e.g. in TrueCrypt) make a difference to the security provided, assuming independant keys? For example: ... 3answers 553 views ### 1 Billion Bit Encryption? So, browsing through YouTube, I stumbled on this video interview of John Draper (Captain Crunch), one of the first "hackers". He talks for about 3 minutes (until 27:48) about his home rolled ... 5answers 404 views ### Using multiple secret keys I have two secret keys. One is a secret key generated by OpenSSL (primary secret key). Second key is generated by performing one way hash operation to GPS co ordinates and time parameters (geo secret ... 3answers 942 views ### AES key reuse and guessing the key Bit of a noob question and a fair bit of Googling didn't help. I understand that the current encryption standard is AES256. A few questions Is the point of this (and other encryption techniques) to ... 2answers 4k views ### If PGP and GPG both follow the OpenPGP standard, are they 100% compatible in all use cases? If someone gives me their PGP key, can I use it with GPG, and vice versa, all the time (100% interchangeable)? Or are there times when they are not compatible, when only PGP can be used with a PGP key,... 3answers 22k views ### AES 256 Encryption - Is it really easy to decrypt if you have the key? So this might sound like a crazy question but bear with me for a minute. I can't find any info on the internet and so am here, although this might have been a good place to start. I've recently ... 1answer 5k views ### Can I remove newlines in a public key? Can I remove new lines from the RSA public key file to get a one line string? So the question is if the key looks like this AAA BBB CCC or ... 2answers 3k views ### How key materials are generated in SSL V3 from master secret The generation of key materials is given by ... 2answers 2k views ### AES key expansion: 256bit key In AES algorithm, in the key schedule, Why does the expansion of a 256 bit key need an extra application of the S-box, unlike the expansion of 128 bit and 192 bit keys ? (The obvious answer would be "... 1answer 792 views ### Is quantum key distribution safe against MITM attacks too? i read this recently: http://www.newscientist.com/article/dn12786-quantum-cryptography-to-protect-swiss-election.html and some parts of this: http://en.wikipedia.org/wiki/Quantum_key_distribution ... 2answers 1k views ### Hash decrypts key, key decrypts cipher… why? I noticed recently that a couple of pieces of encryption software (TrueCrypt being one of them) don't directly use a hash of the password as the key for the block cipher. Instead, they generate a ... 1answer 446 views ### What is 'key agility' in relation to symmetric-key encryption? I sometimes see, in discussions of symmetric ciphers, reference to the 'key agility' of a particular algorithm. It seems to be related to the difficulty of switching encryption keys, but I don't ... 4answers 2k views ### Creating an encryption key from several other keys and using hash functions I want to combine two or more keys to create a single encryption key that relies on all of them. What is the proper method for doing that? Simple XOR? Using hash functions? Something else? I ... 1answer 254 views ### Is it OK to use a data-encryption key for key wrapping, too? Our industry (area of cheap networked devices) has a standard that defines the usage of keys for both authentication and encryption using EAX mode of AES. This standard does not define key management, ... 1answer 134 views ### Generating a key to use with AES I'm going paperless, and I want to encrypt the documents that I scan. I'd like to use CommonCrypto to perform AES-XTS encryption on each file. I'm a software engineer, and I like the idea of being ... 4answers 1k views ### How to require two keyholders to decrypt a document? I want to create a system to encrypt a document and store it with a 3rd party, but not have the 3rd party be able to decrypt it until some unspecified later date. It seems like the solution would be ... 4answers 904 views ### What is the actual difference between security through obscurity and true encryption? In an abstract sense, aren't both the same? Don't their definitions boil down to the following? security through obscurity: trying to make sure some information cannot be obtained without knowing ... 2answers 1k views ### DES — Can I recover the key when I have both ciphertext and the plaintext? Given a message and DES encrypted form of said message, is it possible to efficiently compute the key used to encrypt the data? 2answers 557 views ### Is Chaocipher a secure cipher under ciphertext-only attack? Chaocipher was invented by John F. Byrne in 1919. The algorithm was recently revealed – see Moshe Rubin's Chaocipher Revealed, the Algorithm (PDF). While a known plaintext attack successfully finds ... 1answer 484 views ### Dan Boneh's Cryptography lecture - problem with 802.11b I am going through Dan Boneh's Cyprography lectures on Coursera. In Lecture 6 https://class.coursera.org/crypto-010/lecture/6 At 7:30 minutes, he discusses the problems with 802.11b design. I ... 1answer 2k views ### RSA example-calculation: Public Key = Private Key (e = d) I am a bit confused. I just calculated manually the single steps of RSA for an implementation with small numbers and suddenly$d$was equal$e$. Please help me understand what I am doing wrong. Here’... 1answer 703 views ### Secure AES Key Generation via Salsa20? I am not creating my own cryptography or anything, but to learn about the Dos and Donts of cryptography, I am looking into AES encryption and ways to generate keys for that. As far as I've understood,... 1answer 378 views ### Why are the random exponents so much bigger in the Socialist Millionaire protocol versus Diffie-Hellman key exchange? Section 8, Security considerations, of RFC3526, which defines groups used for Diffie-Hellman has a table recommending some random exponent sizes. In particular, it says: The strength of a key ... 1answer 1k views ### How does a key wrapping like RFC 3394 secure my cryptographic keys? So I'm messing around in the BouncyCastle library with the RFC 3394 AES Key Wrap engine and I'm trying to understand the benefit of it. The problem I'm running into is how to store keys securely on a ... 1answer 484 views ### For a given plaintext-ciphertext pair, how many valid AES keys are there? For$PT\in \mathbb{M}$and$CT\in \mathbb{C}$, let$\mathbb{F}=\{f|f:\mathbb{M}\rightarrow\mathbb{C}\}$be the collection of all functions from$\mathbb{M}$to$\mathbb{C}$. Then AES encryption under ... 1answer 787 views ### Client and server using same SSL certificate - any issues? I'm working on software where multiple components will communicate with each other using SSL. There would be one central component acting as a server, which would also require the clients to present ... 2answers 949 views ### Using bad generator in ElGamal Encryption Suppose Alice chooses a random Prime$p$and a random private Key$a \in \mathbb{Z}^*_p$. By accident, she also chooses a random number$g \in \mathbb{Z}^*_p$, which is not a generator of$\mathbb{Z}^*...
I've long been looking for a symmetric encryption scheme (or algorithm) with equivalent keys. Let me define what I want: Symmetric encryption algorithm with encryption function $E_k$ and inverse ...