Encryption is the process of transforming plaintext using a cipher to make it unreadable to anyone except those possessing the key.

learn more… | top users | synonyms

8
votes
2answers
952 views

Can someone explain the ECB Penguin?

I've seen the ECB Penguin used to demonstrate why ECB is not a recommended method of encryption, but I do not understand how this translates to text or passwords. Aren't the people who create these ...
8
votes
4answers
446 views

Can I determine if a user has the wrong symmetric encryption key?

We're using the Objectivity/DB object database with a custom encryption plugin that encrypts serialized objects on disk. Encryption uses AES with a shared secret key held by all users. I would like to ...
8
votes
5answers
299 views

Reduction from signatures to encryption?

Is it possible to construct an (asymmetric) encryption scheme from a signature scheme? If the signature scheme is deterministic and allows existential forgery (e.g. RSA), then the answer is yes ...
8
votes
4answers
4k views

What is the effect of the different AES key lengths?

How does a changing key length affects the ciphertext, not only in case of AES, but in general? I know that the key spaces become much larger and the number of rounds in case of AES changes, but is ...
8
votes
2answers
461 views

Why should I use Authenticated Encryption instead of just encryption?

There are various different modes of operation for block cipher use, some of which provide "encryption" and some of which provide authenticated encryption. Why should I use an authenticated ...
8
votes
3answers
237 views

AES CTR with similar IVs and same key

Lets say there is a piece of software that uses AES CTR to encrypt different messages using the same key but with slightly different IVs So for example, a 16 byte IV, the 2nd 8 bytes are always the ...
8
votes
3answers
286 views

Encrypting files with known headers

If I encrypt a file of a known format that has a lengthy header (e.g. an XML Excel file), does that render the encrypted file susceptible to a "known plain text" attack? In other words, if the first ...
8
votes
2answers
2k views

What's 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 ...
8
votes
5answers
335 views

Choose a random number that is different from a bunch of other secret numbers

I'm looking for an algorithm where n participants each have a different secret number between $[0..x]$ (and where $x$ is known) and where the participants then select randomly another, non-secret, ...
8
votes
1answer
814 views

AES and perfect ciphers

I'm taking a crypto class this semester and after learning the definition of a perfect cipher. I started wondering how this definition applies to AES. Obviously AES isn't a perfect cipher, since the ...
8
votes
1answer
429 views

How would one crack a weak but unknown encryption protocol?

I asked a question on security.stackexchange, but was told it would be a better fit here: http://security.stackexchange.com/questions/32779/how-would-one-crack-a-weak-but-unknown-encryption-protocol ...
8
votes
2answers
7k views

What's the fundamental difference between Diffie-Hellman and RSA?

What is the difference in the purpose of DH and RSA? Aren't they both public-key encryption?
8
votes
4answers
257 views

Is there a public key encryption scheme with optimal key size?

Symmetric encryption schemes such as AES have known security levels equal to their key sizes (i.e. breaking an encryption with an $n$ bit key needs about $2^n$ work steps). Elliptic curve encryption ...
8
votes
1answer
118 views

Is the Couvreur et al. polynomial time attack on McEliece practical?

There's a new e-print out on arXiv titled "A Polynomial Time Attack against Algebraic Geometry Code Based Public Key Cryptosystems" by Alain Couvreur, Irene Márquez-Corbella and Ruud Pellikaan: ...
8
votes
2answers
207 views

Voting scheme where the votes become public when a threshold is reached

Does there exist a voting scheme where voters cast private encrypted votes that automatically become public only after the threshold number of votes is cast? It needs to be done without a central ...
7
votes
3answers
612 views

Is this encryption algorithm build from MD5 secure?

I'm being asked to use an encryption algorithm in my code, and besides the fact that I'm sure there will be implementation faults that lead to vulnerabilities, I also have concerns about the algorithm ...
7
votes
4answers
1k views

Is it feasible to build a stream cipher from a cryptographic hash function?

A few years ago I devised a symmetric-key system that worked like so: ...
7
votes
3answers
1k views

Why programming languages don't provide simple encryption methods?

In c#, there is a namespace called System.Security.Cryptography and there are many classes in this namespace, which help developers encrypt and decrypt data. ...
7
votes
2answers
2k views

Is there a way to make RC4 (ARCFOUR) secure, or is it completely broken?

I need a method to authenticate a process with another in order to establish interprocess communication between them, to prevent malicious processes from trying to hook onto the system. Currently I ...
7
votes
5answers
2k views

Are there any simple and yet secure encryption algorithms?

Being very new to C++ and cryptography, I finally managed to implement a version of the Vinegere algorithm. I would like to try something a bit more complicated. I have looked at AES and DES and ...
7
votes
3answers
11k views

Difference between stream cipher and block cipher

A typical stream cipher encrypts plaintext one byte at a time, although a stream cipher may be designed to operate on one bit at a time or on units larger than a byte at a time. A block cipher ...
7
votes
3answers
874 views

Using a Non-Random IV with modes other than CBC

The weakness CWE-329 is an interesting problem with CBC mode. However, does this same weakness affect the other modes of operation that rely upon an IV such as: PCBC, CFB and OFB? My gut feeling is, ...
7
votes
2answers
207 views

Will varying plaintext compensate for a fixed initialisation vector?

This is a follow-up question to Relative merits of AES ECB and CBC modes for securing data at rest. I need to store encrypted Personal Account Numbers (PANs) in a database. The only encryption option ...
7
votes
2answers
570 views

Is the encryption of a hash a good MAC?

At university we were told that it is a bad idea to implement a MAC by simply concatenating a key with the data to sign and to run it through a hash function (e.g. $s = ...
7
votes
2answers
2k views

What is the purpose of four different secrets shared by client and server in SSL/TLS?

I was looking through the working of SSL V3, and found that a connection state is defined by a set of things, including client write mac secret, server write mac secret, server write key, client ...
7
votes
2answers
2k views

What advantage does facebook's new encrypted access_token have?

When a user on facebook grants an app access to their account, an API key is issued to the app. This key is app and user-specific. This process is described in Facebook's developer documentation. ...
7
votes
1answer
393 views

Why are cryptography algorithms not exported to certain countries?

There have been strict laws about the export of crypto software to certain countries. I can understand the intent, but never gauged the fact that there is nothing stopping these countries from ...
7
votes
2answers
376 views

Encrypting 8 times with 8-bit key beneficial?

I was trying to understand cryptography from the book Information Security by Mark Stamp and I am confused by something. Suppose that Alice has a secure block cipher, but the cipher only uses an ...
7
votes
1answer
243 views

Is there a cryptographic function or system in which it becomes HARDER to break as time passes?

Is there a function or system which is time depending in which the effort required to brute force the decryption increases with time? It is easy to break encryption from many years ago because ...
7
votes
1answer
1k views

Is AES-256 a post-quantum secure cipher or not?

We know Grover's algorithm speedup brute-force attacks two time faster in block ciphers (e.g brute-forcing 128 bit keys take $2^{64}$ operations not $2^{128}$). That explains why we are using 256 bit ...
7
votes
1answer
206 views

What does a “cycle” mean in cryptography benchmarks?

In this table of the "Crypto++ 5.6.0 Benchmarks", for example, cryptographic algorithm performance is measured in cycles per byte for symmetric ciphers, and in cycles per operation for asymmetric ...
7
votes
2answers
2k views

How does order-preserving encryption work?

Order-preserving encryption (OPE) is, apparently, a method of encrypting data so that it's possible to make efficient inequality comparisons on the encrypted items without decrypting them. I've been ...
7
votes
2answers
1k views

How will Cryptography be changed by Quantum Computing?

I realise this isn't a 'yes or no' question, and I apologise for asking something that could be seen as a discussion thread, but I had to ask. I'm currently doing an EPQ in CS (specifically how QC ...
7
votes
2answers
246 views

K out of N encryption

A friend just showed me how to combine padlocks to achieve a lock that opens when k out of n people turn their keys. I was ...
7
votes
1answer
426 views

CBC key lifetime, or, “how big is too big?”

IPSec recommends rekeying SA's figuring in both time and amount of data sent. Even when using AES-256 in CBC mode, the key and IV commonly get re-negotiated after 100MB. My case isn't using IPSec, ...
6
votes
3answers
2k views

How to attack a classical cipher using known partial plaintext?

I have a ciphertext generated by a classical cipher. I do not know what was cipher used to generate it. I do however have the beginning of the plaintext. What are the cryptanalysis approaches for ...
6
votes
4answers
4k views

How can one securely generate an asymmetric key pair from a short passphrase?

Background info: I am planning on making a filehost with which one can encrypt and upload files. To protect the data against any form of hacking, I'd like not to know the encryption key ($K$) used for ...
6
votes
3answers
629 views

Any practical uses of machine learning for cryptography?

I am about to go study for my masters in machine learning, data mining and high performance computing, but have recently become very interested in cryptography after taking Dan Boneh's Cryptography ...
6
votes
3answers
1k views

Why is the IV passed in the clear when it can be easily encrypted?

The initialization vector (IV) is exclusive or'd against the plain text before encryption for the first block sent in order to prevent an attacker from learning that duplicate message blocks are being ...
6
votes
2answers
415 views

Is it possible to create an easy to use encryption/decryption method that will never be comprimised?

In the comments of the question "Why programming languages don't provide simple encryption methods?" the following statement was made: A well thought out, tested and understood standard that has ...
6
votes
3answers
2k views

Encryption/ciphers/codes in Chinese

I am quite curious as to how you can perform simple encryption for the Chinese language. Saw a similar question related to encryption/Chinese here: About cryptography in a character language, ...
6
votes
2answers
779 views

Constructing a block-cipher from a hash function

It is possible to use a hash function to construct a block cipher with a structure similar to DES? Because a hash function is one way and a block cipher must be reversible (to decrypt), how is it ...
6
votes
4answers
6k views

Difference between encrypting something and hashing something

What is the difference between encrypting something and hashing something? in what situations would I want one or the other?
6
votes
2answers
904 views

Why is ciphertext from low entropy plaintext not compressible?

This comes following a discussion with a colleague. My plaintext file plain consists of a about 100,000 lines of "all work and no play...". It's size is: 2.2 MB. ...
6
votes
3answers
2k views

How does the key schedule of Rijndael looks for keysizes other than 128 bit?

It said in Wikipedia that: [....] Rijndael can be specified with block and key sizes in any multiple of 32 bits, with a minimum of 128 bits. The blocksize has a maximum of 256 bits, but the ...
6
votes
1answer
520 views

How exactly was the finalist chosen in the NIST AES competition?

I was just reading the Stick Figure Guide to AES and came across an interesting table explaining how the winner was chosen: Unfortunately the NIST site is down so I can't gain further information ...
6
votes
3answers
399 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 ...
6
votes
2answers
376 views

How does Clifford Cocks 'Non-Secret Encryption' work?

I have read Clifford Cocks "A Note on 'Non-secret Encryption'" and thought I would try to implement this, but I don't seem to be able to get it to work. I'm obviously missing something. From the ...
6
votes
1answer
1k views

Why is CBC with predictable IV considered insecure against CPA

I just learned that using CBC encryption with an IV which is predictable is not secure. From what I understand, using certain plain texts, and then guessing the IV that is uses, the attacker can ...
6
votes
1answer
3k views

How do I correctly derive a Key and IV?

Mainly I'm trying to understand how to correctly create the Key and IV for use with the .NET Implementation of AES (AesManaged class). This encryption code will be used in conjunction with existing ...