Develop Reference

C# AES remove trailing null characters

I'm new to the cryptography topic, so I wanted to try out AES. My problem is, that after decryption, the target buffer would have trailing '\0' characters. I guess this happens because the data is encrypted in blocks and my cipher-byte[] is bigger than the initial data. Is there a fancy way to handle this? My current solution looks this:
using (MemoryStream ms = new MemoryStream(cipher)) {
using (CryptoStream cs = new CryptoStream(ms, decryptor, CryptoStreamMode.Read)) {
byte[] cipherBuffer = cs.Read(cipher.Length);
int i = cipherBuffer.Length - 1;
while (i >= 0 && cipherBuffer[i] == '\0')
i--;
byte[] targetBuffer = new byte[i + 1];
Array.Copy(cipherBuffer, targetBuffer, i + 1);
return targetBuffer;
}
}
Let's say I want to encrypt an Image that actually has a trailing '\0', then this code would create a wrong result.
I tried looking for a way that this trailing null character removal is done oob but I didn't find any other solution to this.

PHP - C# translated hashing function not working?

I'll get right to the question,
We have this block of C# code
using (Rfc2898DeriveBytes pbkdf2 = new Rfc2898DeriveBytes(password, passwordSaltBytes, iterationCount))
{
pbkdf2Bytes = pbkdf2.GetBytes(derivedLength + iterationCountBytes.Length);
}
Returns a byte array, first index has a value of 252
We attempt the same thing in PHP:
$key = hash_pbkdf2("SHA1", $password, $password.$salt, $iterationCount, 48);
First index is 102...
The values all match before this specific part.
It's just that hashing function that isn't giving me consistent results.
Any help is appreciated, cheers.
Edit - If it's not obvious, I'm trying to understand why those two values don't match, what encoding/decoding etc. am I misunderstanding or doing incorrectly.

This is the full C# code. As you can see there are some unnecessary loops etc. but the reasons why this wasn't working are 2:
As somebody pointed out, the bytes in PHP do no output raw data by default, and thus the hash (and consequently as such,) its bytes, weren't identical with that of the C# script.
Previously, I thought (as others also pointed out) that I should pass in the $salt as it is without any encoding or transformation. But upon looking closer at the actual C# code... we can see in the 2nd for i loop that they're actually appending saltBytes onto passwordBytes, thus creating something similar to $password.$salt in PHP
Combining the two above issues:
Sending the $password.$salt instead of just one, and then setting the $raw_output option to true, outputs the same hash, the same bytes as C# does.
byte[] passwordBytes = Encoding.UTF8.GetBytes(password);
byte[] saltBytes = Encoding.UTF8.GetBytes(salt);
byte[] iterationCountBytes = BitConverter.GetBytes(iterationCount);
int derivedLength = passwordBytes.Length + saltBytes.Length;
byte[] passwordSaltBytes = new byte[derivedLength];
byte[] pbkdf2Bytes;
string encryptedString;
for (int i = 0; i < passwordBytes.Length; i++)
{
passwordSaltBytes[i] = passwordBytes[i];
}
for (int i = 0; i < saltBytes.Length; i++)
{
passwordSaltBytes[passwordBytes.Length + i] = saltBytes[i];
}
using (Rfc2898DeriveBytes pbkdf2 = new Rfc2898DeriveBytes(password, passwordSaltBytes, iterationCount))
{
pbkdf2Bytes = pbkdf2.GetBytes(derivedLength + iterationCountBytes.Length);
}
Thanks.

c# How to generate RSA Key pair from Random Numbers generated using PRNG

I have generated random number using RNGCryptoServiceProvider, the next requirement is to generate a private, public RSA key pair which can be used for encryption/decryption purposes.
How to construct the RSAParameters object using that random number, because the RSA parameters can be imported to create RSACryptoServiceProvider object which will eventually used to encrypt the raw data.

This is how I converted the random number to private/public key pair using BouncyCastlelink
byte[] btRandomNumber = new byte[1000000];
using (RNGCryptoServiceProvider r = new RNGCryptoServiceProvider())
{
r.GetBytes(btRandomNumber);
}
int RsaKeySize = 1024;
Org.BouncyCastle.Security.SecureRandom secureRandom = new Org.BouncyCastle.Security.SecureRandom(btRandomNumber);
var keyGenerationParameters = new Org.BouncyCastle.Crypto.KeyGenerationParameters(secureRandom, RsaKeySize);
var keyPairGenerator = new Org.BouncyCastle.Crypto.Generators.RsaKeyPairGenerator();
keyPairGenerator.Init(keyGenerationParameters);
Org.BouncyCastle.Crypto.AsymmetricCipherKeyPair keyPair = keyPairGenerator.GenerateKeyPair();
Welcome to any corrections or some other way to do this

Byte to value error

So in c#, I have needed a random below given number generator and I found one on StackOverFlow. But near the end, it converts the byte array into a BigInteger. I tried doing the same, though I am using the Deveel-Math lib as it allows me to us BigDeciamals. But I have tried to the array change into a value, and that into a String but I keep getting a "Could not find any recognizable digits." error and as of now I am stumped.
public static BigInteger RandomIntegerBelow1(BigInteger N)
{
byte[] bytes = N.ToByteArray();
BigInteger R;
Random random = new Random();
do
{
random.NextBytes(bytes);
bytes[bytes.Length - 1] &= (byte)0x7F; //force sign bit to positive
R = BigInteger.Parse(BytesToStringConverted(bytes)) ;
//the Param needs a String value, exp: BigInteger.Parse("100")
} while (R >= N);
return R;
}
static string BytesToStringConverted(byte[] bytes)
{
using (var stream = new MemoryStream(bytes))
{
using (var streamReader = new StreamReader(stream))
{
return streamReader.ReadToEnd();
}
}
}
Deveel-Math

Wrong string conversion
You are converting your byte array to a string of characters based on UTF encoding. I'm pretty sure this is not what you want.
If you want to convert a byte array to a string that contains a number expressed in decimal, try this answer using BitConverter.
if (BitConverter.IsLittleEndian)
Array.Reverse(array); //need the bytes in the reverse order
int value = BitConverter.ToInt32(array, 0);
This is way easier
On the other hand, I notice that Deveel-Math's BigInteger has a constructor that takes a byte array as input (see line 226). So you should be able to greatly simplify your code by doing this:
R = new Deveel.Math.BigInteger(1, bytes) ;
However, since Deveel.Math appears to be BigEndian, you may need to reverse the array first:
System.Array.Reverse(bytes);
R = new Deveel.Math.BigInteger(1, bytes);

Incremental Hashing in WinRT/Metro

I'm porting some code that uses incremental SHA-1 heavily:
SHA1 hasher = HashAlgoFactory.Create<SHA1>();
hasher.Initialize();
DiskIOCallback readCallback = null;
readCallback = delegate(bool successful) {
if (successful)
hasher.TransformBlock(hashBuffer, 0, count, hashBuffer, 0);
offset += count;
if (!successful || offset == endOffset)
{
object hash = null;
if (successful)
{
hasher.TransformFinalBlock(hashBuffer, 0, 0);
hash = hasher.Hash;
}
And am looking for a WinRT/Metro equivalent. I've used hasher.HashData before; is there some relatively simple way to get incremental behaviour out of HashData, or some alternative that implements the same functionality as above (in a WinRT/Metro way)? It's entirely possible I'm missing something obvious...

You should use CryptographicHash class:
var hashProvider = HashAlgorithmProvider.OpenAlgorithm(HashAlgorithmNames.Sha1);
var hasher = hashProvider.CreateHash();
You can append multiple increments of data:
hasher.Append(bytesPart.AsBuffer());
Once you're done, you retrieve the hash:
var hash = hasher.GetValueAndReset().ToArray();