MD5 HashCode in C#.NET

Question

How can a bypass the 8000 limit characters of creating hashcode in SQL Server 2012,

 select SUBSTRING(sys.fn_sqlvarbasetostr(HASHBYTES('MD5', 'Sample
 string with more than 8000 Characters')),3,32) as MD5HashCode

I try to work with C# syntax.

String  str = "Sample string with more than 8000 Characters"
System.Security.Cryptography.MD5CryptoServiceProvider x = new System.Security.Cryptography.MD5CryptoServiceProvider();
byte[] bs = System.Text.Encoding.Unicode.GetBytes(str);
bs = x.ComputeHash(bs);
System.Text.StringBuilder s = new System.Text.StringBuilder();
  foreach (byte b in bs)
  {
    s.Append(b.ToString("x2").ToLower());
  }

But the computed HashCode SQL Query is different in C# Syntax.

Thanks in Advance.

Possible duplicate of [TSQL md5 hash different to C# .NET md5](http://stackoverflow.com/questions/27908449/tsql-md5-hash-different-to-c-sharp-net-md5) — Mark, Aug 05 '16 at 06:31

score 2 · Accepted Answer · edited Jan 19 '20 at 19:48

When using SQL Server’s varchar data type the .Net encoding to go with is UTF8 since it’s the fastest and most optimized of the three (ASCII, UTF7, UTF8). When using the nvarchar data type to go is Unicode (UTF16) but we also have to know the texts endianness to create correct hashes.

Examples:

DotNet:

string source = "Sample string with more than 8000 Characters";
using (MD5 md5Hash = MD5.Create()) 
{ 
    Console.WriteLine(GetMd5Hash(md5Hash, source, System.Text.Encoding.ASCII)); <br/>Console.WriteLine(GetMd5Hash(md5Hash, source, System.Text.Encoding.UTF7));
    Console.WriteLine(GetMd5Hash(md5Hash, source, System.Text.Encoding.UTF8));  
    Console.WriteLine(GetMd5Hash(md5Hash, source,System.Text.Encoding.Unicode)); 
    Console.WriteLine(GetMd5Hash(md5Hash, source, System.Text.Encoding.UTF32)); 
}

DotNet Image

Database:

-- note the size 15 of all datatypes

declare @val1 varchar(50),
    @val2 nvarchar(50),
    @val3 char(50),
    @val4 nchar(50)

-- example of 1 byte/char text
-- all variables are of same length

select  @val1 =  'Sample string with more than 8000 Characters'
    @val2 = N'Sample string with more than 8000 Characters',
    @val3 =  'Sample string with more than 8000 Characters',
    @val4 = N'Sample string with more than 8000 Characters'

-- all 4 return different results

select  HASHBYTES('md5', @val1) as MD5_varchar,    
-- result = 0xAE1C585474D90965ED832A7E588D4AF4
-- just to show that collation doesnot change the hash
HASHBYTES('md5', @val1 collate Cyrillic_General_BIN2) as MD5_varchar_collation, 
-- result = 0xAE1C585474D90965ED832A7E588D4AF4
HASHBYTES('md5', @val2) as MD5_Nvarchar,    
-- result = 0x880632484491D1283818B7A3AE3D2AFC
HASHBYTES('md5', @val3) as MD5_char,        
-- result = 0x77D2A2CF22998C4CD5AD5550664BF931
HASHBYTES('md5', @val4) as MD5_Nchar        
-- result = 0x9B55DF00EAFE01D764BB944592C27521

Database Image

Thanks for your explanation , now I realized the difference between each Encoding type. I Ichoose UTF8. — Edeliza Calago, Aug 05 '16 at 09:50

MD5 HashCode in C#.NET

1 Answers1