# All Questions

549 views

### Combining multiple symmetric encryption algorithms - implications?

I was just wondering if I add more security by combining two or more symmetric encryptions on a plain text. For example: Plaintext → AES → Twofish → Serpent Of ...
130 views

### What's the advantage of using OFB/CFB/CTR modes over a stream cipher

As far as I understand: The primary disadvantage associated with stream ciphers is the need for a random and unique key for each run in order to protect against reused-key attacks. OFB/CFB/CTR block ...
146 views

### how much trust can we place in protocol verifiers? [closed]

I read many papers on authenticated key exchange protocols, and most security proofs are done by the authors. In this method, you can imagine that the efficiency is low. Moreover, even if you have ...
94 views

### Need to generate new DH keys for every message in OTR

Going through the OTR specification I don't quite get why a new DH keys (and hence new symmetric key and hmac key) are generated for each message to be sent. Why is this necessary? I don't think it ...
220 views

### Uniform distribution/randomness of characters in the sha256 hash?

I'm using the sha256 algorithm to generate a number in one of my programming projects. A sha256 hash is calculated from three strings: one the user can edit, one the user can view but not edit and one ...
129 views

### How to handle the GCD(V,P) != 1 case when doing point addition or point doubling in elliptic curve cryptography

The equation for a finite field Elliptic Curve is of this form: $$y^2 \equiv x^3 + a * x + b \pmod{P}$$ When we do common EC operations like point doubling or point addition we need to calculate the ...
188 views

### PBKDF2-SHA512 - Does a Big Salt Decrease Security?

I use PBKDF2-SHA512 with an iteration count of 128,000 to hash my passwords. I use a CSPRNG to generate a salt per password. However, I am unsure about the ideal size of the salt. I have read a lot of ...
172 views

### Analyzing ECB's and CBC's resistence to a known-plaintext attack

I'm trying to analyze the strength of a block cipher with CBC mode or with ECB mode on the scenario of an exhaustive search attack with knowledge of pairs of plaintext – ciphertext (known plaintext ...
183 views

### KDF followed by a Hash?

It is my understanding that a KDF adds entropy, whereas a hash loses information. I've read that KDF should be used to store passwords. I don't understand why we don't use a KDF and then a hash, so ...
437 views

### RSA and ECDSA performances

Signature algorithms with elliptic curves have small output sizes compared to RSA for the same level of security. What about the processing time to generate a signature ? I've seen figures giving ...
39 views

### Common pitfalls of session key activation?

Assume that initiator $I$ and responder $R$ of a key agreement protocol have agreed on new symmetric session keys $K'_{auth}$ and $K'_{enc}$, e.g. by way of Diffie-Hellman and key derivation, possibly ...
219 views

### Most frequently used digital signature schemes in the recent years

I am looking to understand if there are any hard figures on which digital signature schemes are most commonly in use today. I'm only really interested in what is employed recently (ie. last couple ...
485 views

### Is the logic for how the enigma machine worked documented somewhere?

I know that there is a formula to calculate the result of any input but is the logic of how the machine actually worked documented? I have seen schematics for the circuitry and even a how to make ...
327 views

### Is TEA considered secure?

Wikipedia claims that the best attack on the surprisingly simple TEA block cipher, that isn't a related-key attack, has a time complexity of $2^{121.5}$. So despite how unsophisticated the cipher ...
381 views

### IV's from Crypto++ AutoSeededRNG always ends the same: Problem with the PRNG? [closed]

I am using a AutoSeededRNG from Crypto++ to generate IVs for use in CBC encryption. I am encoding the IVs using Base64 for future use (decryption). I notice that ...
203 views

### Any techniques for evading frequency based crypt analysis without encrypting?

Are there any general techniques for evading frequency based crypt analysis without using any encryption techniques?
244 views

### Is there a “brainwallet” for GPG keys? [closed]

“Brainwallet” is a program that takes a passphrase (hopefully a good one) and deterministically creates a Bitcoin wallet. This wallet can be used for transactions, then deleted from the computer. To ...
196 views

### Does ECIES imply authenticity?

Assume: Alice and Bob both generate separate EC keypairs Alice obtains Bob's public key, and together with her private key creates a shared secret key Alice encrypts a message using the shared key ...
267 views

I'm relatively new to encrypting, and I have some questions. I intend to write a standalone C# program that will write and read an encrypted file with sensitive data using a password entered by the ...
748 views

### Is there an intuitive explanation as to why only the private key can decrypt a message encrypted with the public key?

I have just learned about using PGP/GPG for email encryption and one thing has always bugged me: How is it possible that a message encrypted with somebody's public key can be decrypted only with that ...
157 views

### Does data authenticity always, implicitly, provide data integrity?

Does a scheme which provides data authenticity (e.g. HMAC or RSA signature) always implicitly provide integrity? It seems, to me at least, that it must by necessity. However, I have seen ...
1k views

### Is sharing the modulus for multiple RSA key pairs secure?

In the public-key system RSA scheme, each user holds beyond a public modulus $m$ a public exponent, $e$, and a private exponent, $d$. Suppose that Bob's private exponent is learned by other users. ...
46 views

### For enciphering messages with AES in CTR mode, do I need a different key for each message?

I have written a program to run AES in CTR mode with keys of 128,192 or 256 bits and checked it gives correct results with the data given in section F.5 at ...
85 views

### How to benchmark custom crypto with OpenSSL benchmark suite? [closed]

OpenSSL benchmark suite currently tests the speed of algorithms supported by the library like md5 sha1 sha256 sha512. What if we have a custom crypto algorithm "abc" . How do we benchmark its ...
84 views

### (n,n) Shamir secret sharing [duplicate]

In (n,n) Shamir secret sharing if n shareholders do not have the public values (X values) can they still obtain the secret with only Y values?
53 views

### How to write the encrypted message after using RSA

I have created a RSA encryption/decryption program but how do i write out the results after doing a encryption? Right now I have it so that it will just print out the decimal value of one character ...
1k views

### Algorithm: How to use x and y mouse movement co-ordinates to generate random data?

Background: I'm making a program for fun as a learning exercise. I want to generate some actual random key material (not pseudorandom) from a JavaScript program. For my program is just for ...
56 views

### Error propogation in CBC mode

Going through the wiki for modes of operation I see that the section error propogation says that an error in one block in the ciphertext in CBC mode only impacts two blocks. I do not quite get that. ...
506 views

### Generating Encryption Keys from Biometric Fingerprint Templates

How would one go about generating Encryption Keys from Biometric Fingerprint Templates extracted from a fingerprint using either Griaule SDK or DigitalPersona SDK or any other SDK that will return the ...
62 views

### Problem with anonymously merging information from distributed sources

Some Background: There is an entity with an identifier and some information. The identifier of this entity is a string with a known scheme/pattern(Which means the total number of such possible ...
244 views

### Encryption and HMAC key derivation

I'm deriving keys from a user-supplied passphrase for symmetric encryption using AES-256 in CBC mode with a HMAC for authenticity/integrity. My key derivation function currently looks like this: ...
68 views

### Pairing Field size as security parameter

I have read Pairings for cryptographers: It states that the groups $G_1$ and $G_2$ are groups of points on the curve and the group GT is a subgroup of the multiplicative group of a related finite ...
74 views

### Is there an anonymous non-interactive authorisation scheme with peer-side auth. signature generation?

I implemented a pseudonymous PKI scheme (by K. Zeng @Springer Link), where all peers can change their public keys including its signature on their own. I am looking for a way to extend it with some ...
293 views

### Is there a public-key cryptography method that enables public keys to be much smaller than private keys?

Does a public key cryptography method that enables the public key to be orders of magnitude smaller than the private key exist?
76 views

### order of elliptic curve divisible by prime

Why order "u" of an elliptic curve "E" defined over a finite field "GF (q)" (u = | E / GF (q) |) must be divisible by a large prime number r to be appropriate for cryptographic purposes?
78 views

### Why would splitting a password output be better than separate HMACs for encryption/authentication key derivation?

In a recent question I asked here on crypto.se, an answer was given that surprised me a bit. As mentioned in the referenced question, I'm looking to derive encryption and authentication keys from ...
138 views

### How can I perform matching on an “encrypted- fingerprint feature matrix” using Fully Homomorphic Encryption?

I am doing a finger-print authentication process. The feature-extraction using minutiae has been done and I get an N x 6 matrix, where the 6 columns are {$x_i$ ...
102 views

### How does this SSL-related flaw work?

I just saw a video at CNN in which it is claimed that, if the server isn't generating a random public key, the server can be hacked. First how HTTPS works… to be sure I’m on the same page: Server ...
179 views

### ECC Complexity order of point addition, scalar point multiplication and selecting random point

I am facing this problem in calculating the order of a process which involves ECC point addition: $P+Q$ , scalar multiplication: $aP$, and selecting random points in the group. The group is of prime ...
105 views

### Journals to read in order to keep up to date with interesting research [closed]

I'd love suggestions from crypto.stack as to academic journals to read. They can range from introductory to advanced, as long as it's free (requires no access fees). Feel free to edit this question ...
93 views

### Efficiency of chaining AES “groups” of blocks

From ISO/IEC 23001-7:2012/Amd 1:2012 10.2.2 Creation of Initialization Vector (Informative) Decryption efficiency may be improved if subsequent initialization vectors use the value of the last ...
798 views

### The use of cribs [closed]

I'm looking to incorporate more crib usage in breaking ciphers in unknown enciphering schemes, or at least to gleam what information I may. This seems to be a big hurdle to me, and I'm looking for ...
177 views

### Why do “nothing up my sleeve numbers” have low entropy?

As a preface, forgive me for some of the links being from Wikipedia. I realize that academia frowns upon this. I came across this article about "nothing up my sleeve numbers". In it, it says: ...
104 views

### Cryptographic pseudo-random generation of address subsets

Suppose I have devices which broadcast, on an insecure channel, 32-bit addresses. I want to make these devices untraceable - one way to do so is to allocate for each device a distinct subset of ...
133 views

### What are the major flaws and limitations of this hash-based stream cipher design?

K is a 224-bit key. C is a 32-bit counter; it is publicly known. the same value is never used twice. ...
101 views

### How does CBC work with read-write volumes?

I have read an article about an attack on LUKS in CBC mode and had a look at the WP article about CBC and now I am confused. If I have understood that correctly then changing the plaintext of a block ...
205 views

### Reverse engineering a single checksum byte [closed]

I am working to understand a system which saves a few bytes of data together with what appears to be a single checksum byte that provides a very naive guarantee that the data has not been tampered ...
317 views

### Calculating amount of time for brute forcing ciphertext depending on the size of the key

I am a graphic design student and for my information graphic project I have chosen the topic of the history of encryption and how the security level developed over the centuries. It’s basically an ...
I'm supposed to show the complement property of DES ($c=DES(p,k) => \bar c = DES(\bar p, \bar k)$). My idea was to just start the algorithm with $\bar p$ and see what happens (ignoring the initial ...