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.

learn more… | top users | synonyms (1)

7
votes
1answer
2k views

Advantages using Diffie-Hellman or Elgamal

For what kind of usage should we prefer using Diffie-Hellman in order to exchange keys instead of Elgamal, and most important why should we use one or the other? I do not see a clear difference ...
7
votes
3answers
3k 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 ...
7
votes
6answers
10k 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?
7
votes
1answer
5k views

Avalanche effect in DES

I couldn't understand the avalanche effect in DES. Could someone explain how avalanche effect happens in DES
7
votes
1answer
460 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
1answer
8k views

What is the difference between CBC and GCM mode?

I am trying to learn more about GCM mode and how it differs between CBC. I already know that GCM provides a MAC which is used for message authentication. From what I have read, and seen code ...
7
votes
1answer
5k 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 ...
7
votes
2answers
623 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 ...
7
votes
2answers
667 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
275 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
2k 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
3k views

How do other, non-RSA algorithms, compare to the PKCS #1 standard?

Arguably the PKCS suite of standards have a profit-oriented bias as they are promoted by RSA and promote their algorithms over others in the form of RFCs and other means. I'm considering the ...
7
votes
2answers
1k 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 ...
7
votes
1answer
559 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, ...
7
votes
0answers
277 views

Is it possible to break enigma code with a todays laptop

I have a 500 characters enigma encoded text. Random rollers were used (not the ones from wikipedia). I know of this flaw. I can guess some words that sould be in the text, but this probably doesn't ...
7
votes
4answers
235 views

Encrypting or HMACing password digests

Assuming I'm using bcrypt to digest passwords, is any additional security gained by either encrypting or HMACing the resulting digests? By requiring a key to compare password hashes, I would expect ...
6
votes
3answers
838 views

Is there benefit to signing unencrypted emails?

I came to this article from another comment on Crypto StackExchange. After reading it, I am wondering if there is any benefit to using a digital signature on unencrypted S/MIME emails?
6
votes
6answers
2k views

Relative security of a Vigenère cipher

Within a closed computer network, I am ciphering some plaintext data as an added security measure. This is below several other layers of protection. For various technical reasons, I am restricted to ...
6
votes
3answers
3k views

Encryption with “constant” initialization vector considered harmful

I try to get the full reasoning behind the above statement. First, after reading articles here and at wikipedia i understand that using an IV only once is good practice. For stream ciphers not doing ...
6
votes
1answer
2k views

Can you explain Bleichenbacher's CCA attack on PKCS#1 v1.5?

I've studied that the Bleichenbacher's CCA attack on PKCS#1 v1.5. is a base to many versions of attacks in the area. I'm trying to understand that attack, but every explanation I saw starts with the ...
6
votes
2answers
468 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
3k 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
1answer
497 views

What do you call one time pad where pseudo-random numbers are used?

What is the encryption method called when pseudo-random numbers are used instead of true random numbers?
6
votes
2answers
984 views

What is the security loss from reducing Rijndael to 128 bits block size from 256 bits?

As you know in the past few weeks it has emerged that NIST/NSA have been involved in weakening encryption standards over a long period of time so that they can retain the ability to break encryption ...
6
votes
2answers
1k 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
3answers
334 views

Stretching passwords for encrypting small files

I would like to know how to store a sensitive file; a credential of sorts. I want to password-protect it, obviously. It would be appropriate - in my application - to prompt the user for the password ...
6
votes
2answers
1k 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
1answer
253 views

What is Perceptual Encryption?

What is "Perceptual Encryption", and where do we use it? I came across it whilst reading a paper on ECC in a multimedia context, from which I quote: Hence, to achieve perceptual encryption, the ...
6
votes
4answers
705 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
302 views

Rely on NSA Suite B Cryptography?

NSA's Suite B Cryptography suggests some cryptographic algorithms for encryption, digital signatures, message digests and key agreements. The selected algorithms and their key size are suggested by ...
6
votes
1answer
3k views

Can you explain “weak keys” for DES?

A weak key for DES is a key $K$ such that $DES_{k_1}(DES_{k_2}(x))=x$ for all $x$. I don't get why are the 4 keys $k_1||k_2$: $1^{112}$, $0^{112}$, $0^{56}||1^{56}$, $1^{56}||0^{56}$ considered as ...
6
votes
1answer
377 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 ...
6
votes
2answers
3k views

Encrypting and obscuring data between site/user without SSL

Im trying to figure out what the best way to encrypt data sent between a webpage and the user(both ways) is, when hosted in an environment that doesn't support SSL. The purpose of encryption would be ...
6
votes
1answer
1k views

Knowing pre-encryption data, can we find the private key CryptoLocker used?

One of our users seems to have been hit by CryptoLocker. As a result, he has a hard drive full of encrypted files. The ransom-ware claims to have used public key encryption on the files. If we know ...
6
votes
2answers
2k views

How can I remove my personal data from my PGP public key?

According to this Q&A-discussion it is possible to remove all personal data (name and mail address) that is attached to a public key. What steps do I have to follow in order to remove all ...
6
votes
1answer
921 views

What causes first block of AES decryption to be garbled, even with correct IV?

I am attempting to duplicate wireshark's packet capture decryption for a TLS HTTP session, where I control the private key of the server. The cipher suite number is 0x00002f, TLS_RSA_AES_128_CBC_SHA ...
6
votes
2answers
1k views

GPG symmetric encryption and javascript

I have a use case where I need to encrypt some text in the browser using javascript. Only the encrypted text will be stored on the server. The user should then be able to take the encrypted result and ...
6
votes
2answers
234 views

How are secure hashing and encryption algorithms proven?

Given that: You should always use proven secure hashing and encryption algorithms, rather than attempting to write your own. What's the process for criteria for an algorithm being proven? Is ...
6
votes
1answer
154 views

How to turn adversary against encryption of zeroes into adversary against random bits?

I recently read the article Nonce-Based Symmetric Encryption by Rogaway, where he presents two different notions of indistinguishability, which he calls ind$ and ind, respectively. Here's the ...
6
votes
2answers
477 views

Deniable Encryption from simple primitives

Is there a deniable encryption scheme $M = E(p_1,k_1,p_2,k_2,...,p_n,k_n), p_j = D(M,k_j)$ of $n$ plaintexts $p_1,p_2,...,p_n$ and $n$ keys $k_1,k_2,...,k_n$, such that we can fix $D$ to be a known ...
6
votes
2answers
809 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 ...
6
votes
4answers
1k 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 ...
6
votes
2answers
207 views

Where is the proof of security of Diffie's cipher?

There is an apparently provably secure cipher that was proposed by Diffie, but enhanced by R.A. Rueppel. The scheme, which was mentioned in Applied Cryptography, works like this: Measure the length ...
6
votes
1answer
1k views

How can I encrypt + authenticate short strings into similar short ciphertexts?

I wish to manipulate short ASCII strings (namely unpredictable domain names) into a form which cryptographically assures authenticity and confidentiality, for use in the local part of email addresses. ...
6
votes
1answer
1k views

Is AES-XTS considered safe to encrypt multiple files with the same keys?

I was wondering if changing the cipher mode to AES-XTS in EncFS would be a sound idea. EncFS uses AES in CBC mode until the last 1KB block, and CFB mode for the last block if ...
5
votes
3answers
2k 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 ...
5
votes
3answers
2k views

What is the importance of Modular arithmetic in cryptography?

Why do we use modular arithmetic so often in Cryptography?
5
votes
5answers
527 views

Do I need to prepare plain text before encryption?

When I want to encrypt chat messages (in ASCII) before sending, whether it brings some bit of security if I add some extra bytes to the message or shuffle it in some way? I can even try to make data ...
5
votes
3answers
633 views

Can I jettison MAC if I already have SHA1(M)?

I'm currently using SSL with AES-CBC and HMAC for a file transfer containing string M. Now suppose Alice already knows SHA1(M) (and the adversary does not), and she downloads M from Bob using only ...
5
votes
2answers
397 views

After implementing a novel encryption algorithm, how would one go about analyzing its security or get help from others in doing so?

Preface: This question was originally asked on Theoretical Computer Science and later on Computer Science. The kind people on cstheory.SE referred me to this web site. It is being repeated here in an ...