Common.cs

// Copyright (c) Microsoft Corporation.
// Licensed under the MIT License.
using System;
using System.Diagnostics.CodeAnalysis;
using System.Security.Cryptography;

namespace Utilities
{
    public class Common
    {
        [SuppressMessage("Microsoft.Security.Cryptography", "CA5354:SHA1CannotBeUsed", Justification = "Not a security related usage - just generating probabilistically unique id to identify a column from its name.")]
        public static Guid GenerateGuidFromName(string name)
        {
            // The algorithm below is following the guidance of http://www.ietf.org/rfc/rfc4122.txt
            // Create a blob containing a 16 byte number representing the namespace
            // followed by the unicode bytes in the name.  
            var bytes = new byte[name.Length * 2 + 16];
            uint namespace1 = 0x482C2DB2;
            uint namespace2 = 0xC39047c8;
            uint namespace3 = 0x87F81A15;
            uint namespace4 = 0xBFC130FB;
            // Write the bytes most-significant byte first.  
            for (int i = 3; 0 <= i; --i)
            {
                bytes[i] = (byte)namespace1;
                namespace1 >>= 8;
                bytes[i + 4] = (byte)namespace2;
                namespace2 >>= 8;
                bytes[i + 8] = (byte)namespace3;
                namespace3 >>= 8;
                bytes[i + 12] = (byte)namespace4;
                namespace4 >>= 8;
            }
            // Write out  the name, most significant byte first
            for (int i = 0; i < name.Length; i++)
            {
                bytes[2 * i + 16 + 1] = (byte)name[i];
                bytes[2 * i + 16] = (byte)(name[i] >> 8);
            }

            // Compute the Sha1 hash 
            var sha1 = SHA1.Create(); // CodeQL [SM02196] False positive: this hash is not used for any sort of crytopgraphy
            byte[] hash = sha1.ComputeHash(bytes);

            // Create a GUID out of the first 16 bytes of the hash (SHA-1 create a 20 byte hash)
            int a = (((((hash[3] << 8) + hash[2]) << 8) + hash[1]) << 8) + hash[0];
            short b = (short)((hash[5] << 8) + hash[4]);
            short c = (short)((hash[7] << 8) + hash[6]);

            c = (short)((c & 0x0FFF) | 0x5000);   // Set high 4 bits of octet 7 to 5, as per RFC 4122
            Guid guid = new Guid(a, b, c, hash[8], hash[9], hash[10], hash[11], hash[12], hash[13], hash[14], hash[15]);
            return guid;
        }

        public static string StringIntern(string str)
        {
            return str != null ? string.Intern(str) : string.Empty;
        }
    }
}