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A CBC Stream Cipher in C# (With wrappers for two open source AES implementations in C# and C)

, 4 Jul 2004
An article on .NET cryptography
/*
 * ---------------------------------------------------------
 * NetSHA.SHA256 .Net Framework implementation of SHA-256
 * 
 * by Jarrod Nelson for ECE 575 Project  
 * --------------------------------------------------------- 
 * Comments:
 * This class contains static methods which
 * implement SHA-256 either on a given file or on
 * a message stored in a byte array.
 * ---------------------------------------------------------
 * 
 */
// http://islab.oregonstate.edu/koc/ece575/04Project/Nelson/NetSHA.htm
using System;
//using System.IO;

namespace sc
{
	/// <summary>
	/// SHA-256 implementation
	/// </summary>
	public sealed class SHA256
	{
		//SHA-256 constants
		private const uint _H00 = 0x6a09e667;
		private const uint _H10 = 0xbb67ae85;
		private const uint _H20 = 0x3c6ef372;
		private const uint _H30 = 0xa54ff53a;
		private const uint _H40 = 0x510e527f;
		private const uint _H50 = 0x9b05688c;
		private const uint _H60 = 0x1f83d9ab;
		private const uint _H70 = 0x5be0cd19;

		/// <summary>
		/// This method take a byte array, pads it according to the 
		/// specifications in FIPS 180-2 and passes to the SHA-256
		/// hash function. It returns a byte array containing 
		/// the hash of the given message.
		/// </summary>
		/// <param name="message">Message to be hashed as byte array</param>
		/// <returns>Message hash value as byte array</returns>
		public static byte[] MessageSHA256( byte[] message )
		{
			int n, pBase;
			long l;
			byte[] m;
			byte[] pad;
			byte[] swap;
			byte[] temp;

			// Determine length of message in 512-bit blocks
			n = (int)(message.Length >> 6);

			// Determine space required for padding
			if( (message.Length & 0x3f) < 56 )
			{			
				n++;
				pBase = 56;
			}
			else
			{
				n+=2;
				pBase = 120;
			}

			// Determine total message length
			l = message.Length << 3;

			// Create message padding 
			pad = new byte[pBase-(message.Length & 0x3f)];
			pad[0] = 0x80;
			for( int i = 1; i < pad.Length; i++ )
				pad[i] = 0;
			m = new byte[n*64];

			// Assemble padded message
			Array.Copy( message, 0, m, 0, message.Length );
			Array.Copy( pad, 0, m, message.Length, pad.Length );
			temp = BitConverter.GetBytes( (long)l );
			swap = new byte[8];
			for( int i = 0; i < 8; i++ )
				swap[i] = temp[7-i];
			Array.Copy( swap, 0, m, message.Length+pad.Length, 8 );

			// Call Hash1 to hash message
			return Hash256( n, m );
		}

		/*
		/// <summary>
		/// This methods takes the name of a file containing
		/// a message to be hashed.  It loads the message and 
		/// calls MessageSHA256 to pad and hash the message.  This
		/// method returns a byte array containing the hash value
		/// for the given file.
		/// </summary>
		/// <param name="fileName">
		/// Name of file containing message to be hashed.
		/// </param>
		/// <returns>Message hash value as byte array</returns>
		public static byte[] FileSHA256( string fileName )
		{
			byte[] m;

			// Open File and read in message
			FileStream messageFile = new FileStream( fileName, 
				FileMode.Open, FileAccess.Read );

			// Check length of file to ensure it is within
			// currently supported range.
			if( Int32.MaxValue > messageFile.Length )
			{
				m = new byte[ (int)messageFile.Length-2 ];
				messageFile.Read( m, 0, (int)messageFile.Length-2 );
			}
			else
				throw new Exception( "File length exceeds current supported size!" );

			messageFile.Close();

			// Call MessageSHA1
			return MessageSHA256( m );
		}
		*/

		/// <summary>
		/// SHA-1 Hash function - This method should only be used
		/// with properly padded messages.  To hash an unpadded 
		/// message use one of the other methods.  This method is
		/// called by other methods once the message is padded
		/// and loaded as a byte array.  For internal use only!
		/// </summary>
		/// <param name="n">Number of 512-bit message segments</param>
		/// <param name="m">Message to be hashed as byte array</param>
		/// <returns>Hash value as byte array</returns>
		private static byte[] Hash256( int n, byte[] m )
		{
			// K Constants			
			uint[] K = { 0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 
						   0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
						   0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3,
						   0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
						   0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc,
						   0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
						   0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7,
						   0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
						   0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13,
						   0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
						   0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3,
						   0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
						   0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5,
						   0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
						   0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208,
						   0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2 };
			// Calculation variables
			uint a, b, c, d, e, f, g, h, temp1, temp2;
			// Intermediate hash values
			uint[] interHash = new uint[8];
			// Scheduled W values
			uint[] w = new uint[64];
			// Final hash byte array
			byte[] hash = new byte[32];
			// Used to correct for endian
			byte[] swap = new byte[4];
			byte[] swap2 = new byte[4];

			// Initial hash values
			interHash[0] = _H00;
			interHash[1] = _H10;
			interHash[2] = _H20;
			interHash[3] = _H30;
			interHash[4] = _H40;
			interHash[5] = _H50;
			interHash[6] = _H60;
			interHash[7] = _H70;

			// Perform hash operation
			for( int i = 0; i < n; i++ )
			{
				// Prepare the message schedule
				for( int t = 0; t < 64; t++ )
				{
					if( t < 16 )
					{	
						for( int j = 0; j < 4; j++ )
							swap[j] = m[i*64+t*4+3-j];
						w[t] = BitConverter.ToUInt32( swap, 0 );	
					}
					else
					{
						w[t] = (uint)( Sigma( 3, w[t-2] ) + w[t-7] 
							+ Sigma( 2, w[t-15] ) + w[t-16] );
						
					}
				}

				//Initialize the five working variables
				a = interHash[0];
				b = interHash[1];
				c = interHash[2];
				d = interHash[3];
				e = interHash[4];
				f = interHash[5];
				g = interHash[6];
				h = interHash[7];
				
				//Perform main hash loop
				for( int t = 0; t < 64; t++ )
				{
					
					temp1 = (uint)( h + Sigma( 1, e ) + Func(true, e, f, g) 
						+ K[t] + w[t] );
					temp2 = (uint)( Sigma( 0, a ) + Func(false, a, b, c ) );
					h = g;
					g = f;
					f = e;
					e = (uint)( d + temp1 );
					d = c;
					c = b;
					b = a;
					a = (uint)( temp1 + temp2 );
				}

				//Compute the intermediate hash values
				interHash[0] = (uint)( (a + interHash[0]) );
				interHash[1] = (uint)( (b + interHash[1]) );
				interHash[2] = (uint)( (c + interHash[2]) );
				interHash[3] = (uint)( (d + interHash[3]) );
				interHash[4] = (uint)( (e + interHash[4]) );
				interHash[5] = (uint)( (f + interHash[5]) );
				interHash[6] = (uint)( (g + interHash[6]) );
				interHash[7] = (uint)( (h + interHash[7]) );
			}
	
			// Copy Intermediate results to final hash array
			for( int i = 0; i < 8; i++)
			{
				swap2 = BitConverter.GetBytes( (uint) interHash[i] );
				for( int j = 0; j < 4; j++ )
				{
					swap[j] = swap2[3-j];
				}
				Array.Copy( swap, 0, hash, i*4, 4 );
			}

			return hash;
		}

		/// <summary>
		/// Performs SHA-256 logical functions.  See FIPS 180-2 for
		/// complete description.  For internal use only!
		/// </summary>
		/// <param name="b">
		/// Boolean value indicating whether the desired function is Ch
		/// </param>
		/// <param name="x">First arguement</param>
		/// <param name="y">Second arguement</param>
		/// <param name="z">Third arguement</param>
		/// <returns>Function results</returns>
		private static uint Func( bool b, uint x, uint y, uint z )
		{
			// Ch function
			if( b )
				return (uint)( (x & y) ^ ((~x) & z) );
			// Maj function
			return (uint)( (x & y) ^ (x & z) ^ (y & z) );
			
		}

		/// <summary>
		/// Performs the SHA-256 shifting and rotating functions.
		/// See FIPS 180-2 for complete details.  For internal
		/// use only!
		/// </summary>
		/// <param name="i">Integer indicating which function to perform</param>
		/// <param name="x">Operand</param>
		/// <returns>Result of rotation/shift</returns>
		private static uint Sigma( int i, uint x )
		{
			uint temp;

			switch( i )
			{
				case 0:
					temp = (uint)( (x>>2) | (x<<30) );
					temp = temp ^ (uint)( (x>>13) | (x<<19) );
					temp = temp ^ (uint)( (x>>22) | (x<<10) );
					break;
				case 1:
					temp = (uint)( (x>>6) | (x<<26) );
					temp = temp ^ (uint)( (x>>11) | (x<<21) );
					temp = temp ^ (uint)( (x>>25) | (x<<7) );
					break;
				case 2:
					temp = (uint)( (x>>7) | (x<<25) );
					temp = temp ^ (uint)( (x>>18) | (x<<14) );
					temp = temp ^ (uint)(x>>3);
					break;
				case 3:
					temp = (uint)( (x>>17) | (x<<15) );
					temp = temp ^ (uint)( (x>>19) | (x<<13) );
					temp = temp ^ (uint)(x>>10);
					break;
				default:
					temp = x;
					break;
			}
			return temp;
		}
	}
}

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