How to MD5 Hash in C#

Creating an MD5 hash in C# is straightforward using the built-in cryptography libraries.

✅ Best Practice: Use System.Security.Cryptography.MD5 for string or file hashing.

Example

using System;
using System.Security.Cryptography;
using System.Text;

string ComputeMD5Hash(string input)
{
    using (MD5 md5 = MD5.Create())
    {
        byte[] inputBytes = Encoding.UTF8.GetBytes(input);
        byte[] hashBytes = md5.ComputeHash(inputBytes);
        
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < hashBytes.Length; i++)
        {
            sb.Append(hashBytes[i].ToString("x2"));
        }
        
        return sb.ToString();
    }
}

Why use MD5.Create()? Creates a cryptographic service provider that calculates MD5 hashes efficiently.

Alternative: Hash a File (More Common Use Case)

For scenarios where you need to hash the contents of a file:

using System;
using System.IO;
using System.Security.Cryptography;

string ComputeFileMD5(string filePath)
{
    using (var md5 = MD5.Create())
    using (var stream = File.OpenRead(filePath))
    {
        byte[] hashBytes = md5.ComputeHash(stream);
        
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < hashBytes.Length; i++)
        {
            sb.Append(hashBytes[i].ToString("x2"));
        }
        
        return sb.ToString();
    }
}

Why hash files this way? Streams the file content directly through the hash algorithm without loading the entire file into memory.

Security Note

⚠️ Caution: MD5 is considered cryptographically broken and unsuitable for security purposes. For security-sensitive applications, use SHA-256 or better:

using (SHA256 sha256 = SHA256.Create())
{
    // Use the same pattern as MD5 examples
    // Just replace MD5.Create() with SHA256.Create()
}

MD5 is still useful for non-security purposes like checksums and data verification.