Develop Reference

Decrypt string using PHP that was encrypted using c#

I need to decrypt a string, returned from an API that was originally encrypted using c# functions based on those here >
http://www.codeproject.com/Tips/704372/How-to-use-Rijndael-ManagedEncryption-with-Csharp
I need to decrypt using PHP.
A password and a key have been provided I've made several attempts to decrypt using openssl_decrypt, but I'm unsure how to use the key in the decryption?
[update] I have been told that the password I have been given is the basis for the iv, and that the padding is PKCS7, the problem is that I have no idea how to create the iv.
I have the following example input/keys, but I'm not sure how to use the password as I've been told it is the iv do I need to pad it to the correct length, if so how?
Original string: 'Mondays Suck'
Password/salt: 'this_is_the_password'
Input key: 'this_is_the_input_key'
Encrypted String: 'mAqsxJaA0jpQdefBPug2tw=='

If there indeed is any ciphertext packing going on, it would be to include the initialization vector (IV), assuming one was even used in the first place.
In short, if I encrypted a string with AES-128:
I'd likely be using PBKDF2 to take a weak passphrase and a salt to generate secret key material used to do the encryption itself.
I'd generate a message-specific (i.e. one-time use) initialization vector for ciphering
I'd then use the secret key [material] and IV generated in the previous steps to encrypt the string using AES-128: E(plaintext, key, iv)
If the string is longer than 16 bytes, I'd have to also use an encryption mode such as CBC, CTR, etc.
For convenience, I would "pack" the IV (not required to be kept secret) in front of the ciphertext by simply concatenating: iv+ciphertext
If I was serious about doing it right, I would generate a message authentication code of the ciphertext and append that as well such that I would now have: iv+ciphertext+mac
On decrypt, I would then verify the MAC before decrypting (if I was to do it right), and I would then need to separate the IV from the ciphertext, and then run it through my decryption routine: D(ciphertext, key, iv).
Another thing to keep in mind is encoding as sometimes we pass around Base64-encoded strings as a more print-friendly format than raw data. You of course would have to decode that before working on unpacking, decrypting, etc.
For academic purposes, I created Crypto Implementation (DRAFT) back when I was teaching myself crypto and wanted to document processes and best practices as well as keep all "moving parts" in view as a reference when I had to work on this stuff. Lots of rules to follow, but all in all, a lot of good learning and professional development opportunities.
Hope that helps some!
Edit: Per my comment below, I just looked at the original source code for the C# implementation. It appears the only way to decrypt this in PHP would be to have a PHP equivalent of C#'s Rfc2898DeriveBytes as this is the part responsible for generating your IV. Study the DecryptRijndael routine and you'll see where it gets the IV from (it basically implies using the same salt). If you truly have no control or influence over the encryption routine, you might be inclined to hack up a solution involving using C# DLLs in PHP and then call the DecryptRijndael method from PHP.

Encrypting passwords for use in Database AES or RijndaelManaged?

I am having a dilemma in choosing which encryption to use.
I have to store passwords in a database. I would like to encrypt the passwords. I am using C# and am looking for reasons between AES and RijndaelManaged.
I have looked for a succinct answer but I can find none which clearly states which is better today.
If one can provide a link, I would appreciate it.

If possible, you should use salted passwords with a one-way hash.
Hash and salt passwords in C#

In looking at this article The Differences Between Rijndael and AES, the differences mentioned are negligible considering you want to only encrypt passwords (assumingly of small length < 30 characters).
Also see Is the RijndaelManaged Class in C# equivalent to AES encryption?

Encrypt string with AES in PHP, and decrypt in C#

I'm trying to find an AES encryption method that will allow me to encrypt a string in PHP and use the encrypted string to be decrypted in C#
Can anyone help me out here. I've looked at nearly all the examples on the net and can't find a matching one that will let me do what I want.
Thanks

The problem with PHP is that mcrypt only supports null padding. C# does not support null padding for good reason, it goes haywire if you're encrypting binary information. If you switch to OpenSSL for your encryption on PHP you will get better padding options. Once you have switched you simply need to ensure the block size, mode and padding options are the same on both sides.

I would recommend phpseclib, a pure PHP AES implementation. It's interoperable with OpenSSL as demonstrated thusly:
AES Encrypt in PHP to decrypt in openssl

How can I encrypt with AES in C# so I can decrypt it in PHP?

I've found a few answers to Encrypt in PHP, and Decrypt in C#, but as yet have been unable to reverse the process...
The background is I want to:
In C#:
AES encrypt a file's contents.
Upload the data (likely via http via POST) to a server.
In PHP:
Receive and save the file.
And in PHP (at a later date):
Decrypt the file.
I specifically want to encrypt it outside of using SSL/TLS (though I might have to do this as well), as I need to know the file remains encrypted (and decryptable!) when stored on the server.
To encrypt in C# I'm using:
Rijndael RijndaelAlg = Rijndael.Create();
RijndaelAlg.KeySize = 128;
RijndaelAlg.Mode = CipherMode.CBC;
CryptoStream cStream = new CryptoStream(fStream, RijndaelAlg.CreateEncryptor(Key, IV),
CryptoStreamMode.Read);
and to decrypt in PHP:
mcrypt_cbc(MCRYPT_RIJNDAEL_128, $key, $buffer, MCRYPT_DECRYPT, $iv);

Generally it only depends on selecting the right options on both sides:
Plaintext character format
how plaintext characters are encoded in the bit string
Padding
how to pad the plaintext to be an exact multiple of the block size
Key length
must be agreed if there is a choice
Key derivation
how to create the bit string to be used for the key
Mode
which mode of encryption to use
Storage format
how we store the ciphertext
Please see here for a lot of information about these things. Especially the padding seems to be the root of most interoperability problems as PHP's mcrypt uses a NULL-padding by default and has no built-in support for any other padding mode, while e.g. .NET doesn't even provide an option to use a NULL-padding (as it may cause issues when encrypting binary data).

I know this was asked a while ago but I thought I'd post my solution for others. I wrote up a quick code example in PHP and C# that lets you encrypt/decrypt both ways. I had a few issues with getting the settings on both sides to work out. A difference in padding would let it decrypt one way but not the other
https://github.com/dchymko/.NET--PHP-encryption
hope that helps some people.

Are you using the same mode with both? I.e. are you using CBC with both (and not ECB). If you don't understand what I just said then drop a comment and I'll explain in detail, as it has fairly major security repercussions.

I had a similar problem a few months ago - I had a project that had to use AES encryption and I had to make sure that the exact same algorithm is used between a C# and A C++ component. I ended up implementing a shared DLL library used by both based on the AES crypto wrapper from this codeplex article:
http://www.codeproject.com/KB/security/WinAESwithHMAC.aspx

MD5 Hashing Given a Key in C#

I've been looking for a way to hash a given string in C# that uses a predetermined key.
On my adventures through the internet trying to find an example i have seen lots of MD5CryptoServiceProvider examples which seem to use a default key for the machine, but none of them that apply a specific key. I need to have a specific key to encode data as to synchronize it to someone else's server. I hand them a hashed string and an ID number and they use that analyze the data and return a similar set to me. So is there anyway to get md5 to hash via a specific key that would be consistent to both.
I would prefer this to be done in C#, but if its not possible with the libraries can you do so with some web languages like php or asp?
Edit: Misunderstood the scenario I was thrown into and after a little sitting and thinking about why they would have me use a key it appears they want a key appended to the end of the string and hashed. That way the server can appended the key it has along with the data passed to ensure its a valid accessing computer. Anyways... thanks all ^_^
Edit2: As my comment below says, it was the term 'salting' I was oblivious to. Oh the joys of getting thrown into something new with no directions.

MD5 is not encryption - it's a hash. It doesn't allow a string to be decrypted.
You're looking for a symmetric encryption algorithm. It uses the same key to encrypt and decrypt. Trying to use encryption functions without understanding them is dangerous. Even if you think you understand them, you can make a mistake.
If you're transferring data to another person's server, you may be better off using something like gpg to encrypt the file using a symmetric key you both agree on over the phone, or perhaps some public-key crypto. This way, you don't write any crypto code, and it's safer (not completely secure, mind you, but safer).
Edit: I'm still trying to decipher your requirements.
MD5 is an unkeyed hash function - there is not key in use at all. So let's say the server sends you a giant string, or a file, and a hash of it. You would then MD5 the string or file, and compare the hash you computed with the hash they sent. If they match - the data was not corrupted in transit. That doesn't mean no one tampered with what they sent you in transit, because MD5 has no "secret sauce" to it. I can md5 anything I want and send it to you.
A HMAC is a keyed hash function. It has a secret ingredient that only you and the group you're communicating with should know - the secret key. If they send you a long string or file, and a HMAC, you can compute the HMAC yourself, compare your HMAC and theirs, and if they match, the data was not corrupted in transit, nor was the data tampered with.

MD5 is a hash function and, strictly speaking, is not used to "encrypt" a string. It produces a 128-bit "Message Digest" (hence the MD in the name) that is used as a kind of fingerprint for the input string.

Tom's right: MD5 is just a one-way hash, you can't decrypt it. Try these links:
Symmetric Key Encryption in C#
Public-Key RSA Encryption in C#

You can use AES from C# to do the type of encryption you are looking for. Here's an article on how.

You should use one of the classes inherited from SymmetricAlgorithm, for instance :
AesCryptoServiceProvider
DESCryptoServiceProvider
RC2CryptoServiceProvider
TripleDESCryptoServiceProvider

So, why does the following test fail if both input strings are identical?
[TestMethod]
public void MD5HashTest()
{
var hash1 = (new MD5CryptoServiceProvider()).ComputeHash(new System.Text.ASCIIEncoding().GetBytes("now is the time for all good men."));
var hash2 = (new MD5CryptoServiceProvider()).ComputeHash(new System.Text.ASCIIEncoding().GetBytes("now is the time for all good men."));
Assert.AreEqual(hash1, hash2);
}