I have a little background of cryptography so forgive me if this is a silly question. Is there a secure way to encrypt a text using AES that produces the same output with the same input?
Edit
What i want is to store emails in a external analytics provider using AES256 or HMAC 256 (this is a company requirement). But i need to be able to decipher them lately and to distinguish between same emails without deciphering them. I know i can do this with two entries, one with AES and another using HMAC. But can i do this with AES alone and still be secure?
Yes and no. There is a mode called ECB, "electronic code book", that will always produce the same output (cipher text) for a given input (plain text) block.
However, unless you only send each plain text block one time, ECB is not secure. At first, an adversary who intercepts an encrypted message won't be able to decipher it. But, just like old time code books, as they continue to monitor encrypted messages and combine that with knowledge of the context in which they were sent, they can eventually break much of your code.
Use of ECB is generally discouraged. For most messaging applications, an AEAD mode like GCM is recommended.
Related
I'm trying to encrypt a string in javascript and then decrypt it back in server using c#. I thought of using System.Security.Cryptography.Rijndael on server side and some AES implementation like this or this on client-side.
I don't know much about cryptography, so basically I generate a key and send it to client and encrypt my text with that key and send it back to server.
My problem is that Javascript AES implementations use a key to encrypt a text but c# Rijndael class uses a key and a vector. where does that vector come from?
AES is just a block cipher, which is a cryptographic primitive. Its purpose is to encrypt one single block of data (16 bytes).
Encryption requires a lot more than that. You need a method to encrypt an arbitrary amount of data, and hopefully in a way that doesn't give away any information. To do this, you need to break the amount of data into blocks, pad the last part to a full block, and then somehow encrypt each block in a clever way. Doing that is the responsibility of the encryption mode.
The most trivial mode (electronic cookbook, ECB), just encrypts each block with the same key, but that's horribly dangerous. Other modes require some sort of initialization state, which needs to be random but can be publicly known.
To encrypt and decrypt your data, you must know both the block cipher and the encryption mode, on both sides, and you must find a way to generate the initial state on the encrypting side and to recover it on the decrpyting side to initialize the encoder and the decoder, respectively.
In a nutshell: You need a lot more information about what you're doing!
This isn't perhaps exactly what you are looking for. But I can think that what you actually need to do is implement SSL.
http://en.wikipedia.org/wiki/Secure_Sockets_Layer
This might solve your problem without needing to get involved with coding cryptography.
I'm building a simple trivia game that has "hangman" style clues (where letters are revealed as the player asks for hints). I don't want to flat out send the answer with the question any user with sufficient smarts could figure it out) - rather I'd like to encrypt answers on the server and decrypt them on the client. Security isn't of huge importance I just want to make the process harder then it's worth for players. I was wondering if anyone could recommend a strategy for doing this?
A simple approach, which might be sufficiently difficult for most users, would be to send the answer and encryption key to the web client (as hidden form fields), and use Javascript to decrypt it on the fly (inside the browser). A simple exclusive-or'ing of the answer string characters with the key string should be sufficient to "shroud" the answer without requiring large amounts of crypto processing on the client side. Using more than one key string might increase the difficulty of cracking it, too.
I'm assuming that you don't want to implement full commercial-grade crypto on the client side, and also assuming that you only want to hide the answers for a few minutes at most.
I am developing a large application and i need encryption when a data is traveling between two machines in different continents. I have never worked on encryption. I want a simple encryption which can be handled in PHP / Ruby / Python without any dependencies.
So i decided to use HMAC SHA1.
$pad=hash_hmac("sha1","The quick brown....","mykey");
This is what i found out after some research on the internet.
How hard it is to decrypt it if someone doesn't know the key? Also, any alternatives to this?
UPDATE - thanks for all the responses. Problem solved.
It's impossible to decrypt it, even if you know the key. HMAC SHA1 is a keyed hash algorithm, not encryption.
A hash is a cryptographic one-way function that always generates a value of the same length (I think SHA1 is 128-bits) regardless of the length of the input. The point of a hash is that, given the output value, it's computationally infeasible to find an input value to produce that output. A keyed hash is used to prevent rainbow table attacks. Even if you know the key you can't reverse the hash process.
For encryption you want to look at AES.
SHA1 is a one-way-hash function, by definition it is not decryptable by anyone. The question becomes if you have a plaintext T that hashes to H. How hard is it to find another T which also hashes to H.
According to Wikipedia, for SHA1, the best known brute force attack would take 2^51 evlautions to find a plain text that matches.
If you need actual encryption where you can reverse the process, you should take a look at AES256.
See:
http://en.wikipedia.org/wiki/Cryptographic_hash_function
For a general discussion on this.
Like Andrew said SHA1 is an hash algorithm and cannot be used for encryption (since you cannot get back the original value). The digest it produce can be used to validate the integrity of the data.
An HMAC is a construct above an hash algorithm that accept a key. However it's not for meant for encryption (again it can't be decrypted) but it allows you to sign the data, i.e. with the same key you'll be able to ensure the data was not tampered with during it's transfer.
Foe encryption you should look at using AES or, if applicable to your application, HTTPS (which will deal with more issues than you want to know about ;-)
SHA-1 , MD-5 are all one way Hashing algorithms.
They just generate a lengthy string. Each and every string when subjected to these functions will yield you a lengthy string which cannot be retained back.
They are far from encryptions.
If you are looking for encryption algorithms , go for AES (Advanced Encryption Standard) , DES (Data Encryption Standard) Algorithms.
As I say, this is a hash, so not an encryption/decryption problem. If you want to implement a straightforward encryption algorithm, I would recommend looking into XOR encryption. If the key is long enough (longer than the message) and your key sharing policy is suitably secure, this is a one time pad; otherwise, it can potentially be broken using statistical analysis.
I'm creating custom registration forms for Forms Based Authentication for a SharePoint 2010 site, and storing passwords as 'Encrypted' in the aspnet_Membership database table.
My setting in web.config shows that the 'decryption' parameter is "AES". My boss is asking that I look to use AES256, as it's more secure, but I'm having trouble working out how to do this. I've been Googling and "stackoverflow-ing", but so far I've not been able to find that one post that either explains what I need to do, or where to look for good information.
My questions, I think, are:
is "AES256" a valid value for the "decryption" parameter of ?
if not, is simply generating a longer "decryptionkey" all that's required to make AES stonger? i.e. if I make my decryption key 64 characters long, would that constitute AES256?
if I'm totally off base with my current thinking, can anyone put me on track, or explain (or link to an explanation of) how to update my web.config to use AES256 rather than the default AES?
Just in case anyone wants to say "You should use Hashed".. been there, discussed that, decision made to use Encrypted. Just thought I'd get that out of the way :)
No, you can only use "AES" as the decryption parameter for the AES algorithm.
Yes, if you generate one that is 256 bits (64 bytes) long, you effectively have AES256. In reality, you could generate one that is 512 bits long, too. The longer this value is, the stronger the encryption.
No need. You seem to be understanding it.
Now, in .NET 4.0, they've enhanced this a bit, allowing SHA256 to be used for validation as well. See MSDN's documentation (archive.org snapshot) for details.
I heard some time that encryption and cipher are not the same thing, if so, what's the difference?
a cipher is a method (algorithm) used for encryption of some text. But english speakers have that habit of making verbs from nouns... hence ciphering became a synonym of encrypting.
Now, the fun part. If you consider decrypt and decipher, now they have different meanings.
decrypt means applying the decryption key to some code
decipher means finding the meaning of some text that was not deliberately encrypted.
In France (I'm french) we also have funny confusion with similar words. We have "chiffrer" (very similar to "cipher") that is the correct word and means encrypt, but we also use the verb "crypter" that means the same thing but is considered as an anglicism (verb built from english "crypted"). When we go for the opposite words "décrypter" and "dechiffrer" we also have different meanings but not like the english ones... "déchiffrer" means the same that both english words decrypt and decipher depending on the case, but "décrypter" is used when you try to get the clear text without the code (it means breaking the code). I believe there is no english word that means that.
Looking at my answer, I wonder if things were not clearer before it.... natural language is definitely some kind of encryption.
You might take a look at this article on the difference between Encryption and Cryptography. It also addresses the definition of cipher in the process.
Excerpts:
What is Cryptography?
In simple terms, cryptography is the science concerned with the study of secret communication.
What is Encryption?
...
... "encryption" basically is some process or algorithm (known as a cipher) to make information hidden or secret. And to make that process useful, you need some code (or key) to make information accessible.
A cipher is an algorithm of encryption. Ex. substitution cipher, permutation cipher, etc.
Encryption is just the process of obfuscating information.
So in a simplistic sense of the idea, you use a cipher to encrypt stuff. :)