SecureStringHasher.cs source code in C# .NET

Source code for the .NET framework in C#

                        
Code:

                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / Xml / System / Xml / Core / SecureStringHasher.cs / 1305376 / SecureStringHasher.cs
                        

                        
                            //------------------------------------------------------------------------------ 
// 
//     Copyright (c) Microsoft Corporation.  All rights reserved.
// 
// [....] 
//-----------------------------------------------------------------------------
 
using System; 
using System.Collections.Generic;
 
namespace System.Xml {

    // SecureStringHasher is a hash code provider for strings. The hash codes calculation starts with a seed (hasCodeRandomizer) which is usually
    // different for each instance of SecureStringHasher. Since the hash code depend on the seed, the chance of hashtable DoS attack in case when 
    // someone passes in lots of strings that hash to the same hash code is greatly reduced.
    // The SecureStringHasher implements IEqualityComparer for strings and therefore can be used in generic IDictionary. 
    internal class SecureStringHasher : IEqualityComparer { 
        int hashCodeRandomizer;
 
        public SecureStringHasher() {
            this.hashCodeRandomizer = Environment.TickCount;
        }
 
#if false // This is here only for debugging of hashing issues
        public SecureStringHasher( int hashCodeRandomizer ) { 
            this.hashCodeRandomizer = hashCodeRandomizer; 
        }
#endif 

        public bool Equals( String x, String y ) {
            return String.Equals( x, y, StringComparison.Ordinal );
        } 

        public int GetHashCode( String key ) { 
            int hashCode = hashCodeRandomizer; 
            // use key.Length to eliminate the rangecheck
            for ( int i = 0; i < key.Length; i++ ) { 
                hashCode += ( hashCode << 7 ) ^ key[i];
            }
            // mix it a bit more
            hashCode -= hashCode >> 17; 
            hashCode -= hashCode >> 11;
            hashCode -= hashCode >> 5; 
            return hashCode; 
        }
    } 
}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.

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