ASP.NET MembershipProvider -- How exactly does it do encryption?

Question

I need to understand the details of how MembershipProvider performs encryption:

1. What algorithm does it use?
2. Is there any base64 encoding pre-processing or post-processing?
3. Anything extra it does in addition to the standard algorithm it uses?

Given a plain text password to encrypt, please walk me through the exact steps that produce the final encrypted password that's returned.

I think seeing the source code would go a long way in answering my questions, but I haven't been able to find it online. I have only found this documentation, which does not provide implementation details.

Thanks for any info!

Answer 1

Below is the code that you want / need... it's a little bit of a rabbit warren getting there, so to fully understand, I would recommend doing the following:

• Install ReSharper
  [Optional] Install dotPeek
• Write the following code anywhere:
  var dummyMembershipProvider = new SqlMembershipProvider();
dummyMembershipProvider.ChangePassword("userName", "oldPassword", "newPassword");
• Ctrl + Left Click (go to definition) on ChangePassword
• This will begin your journey down the rabbit warren... it should look something like this:
  SqlMembershipProvider.ChangePassword
SqlMembershipProvider.EncodePassword
MembershipProvider.EncryptPassword
IMembershipAdapter.EncryptOrDecryptData
MembershipAdapter.EncryptOrDecryptData
MachineKeySection.EncryptOrDecryptData
• Purchase ReSharper because you realise you can't live without it anymore

Anyway, here's the MachineKeySection.EncryptOrDecryptData:

public sealed class MachineKeySection : ConfigurationSection
{
    internal static byte[] EncryptOrDecryptData(bool fEncrypt, byte[] buf, byte[] modifier, int start, int length,
                                                bool useValidationSymAlgo, bool useLegacyMode, IVType ivType)
    {
        EnsureConfig(); 

        if (useLegacyMode) 
            useLegacyMode = _UsingCustomEncryption; // only use legacy mode for custom algorithms 

        System.IO.MemoryStream ms = new System.IO.MemoryStream(); 
        ICryptoTransform oDesEnc = GetCryptoTransform(fEncrypt, useValidationSymAlgo, useLegacyMode);
        CryptoStream cs = new CryptoStream(ms, oDesEnc, CryptoStreamMode.Write);

        // DevDiv Bugs 137864: Add Random or Hashed IV to beginning of data to be encrypted. 
        // IVType.None is used by MembershipProvider which requires compatibility even in SP2 mode.
        bool createIV = ((ivType != IVType.None) && (CompatMode > MachineKeyCompatibilityMode.Framework20SP1)); 

        if (fEncrypt && createIV)
        { 
            byte[]  iv       = null;
            int     ivLength = (useValidationSymAlgo ? _IVLengthValidation : _IVLengthDecryption);
            switch (ivType)
            { 
            case IVType.Hash:
                iv = GetIVHash(buf, ivLength); 
                break; 
            case IVType.Random:
                iv = new byte[ivLength]; 
                RandomNumberGenerator.GetBytes(iv);
                break;
            }
            Debug.Assert(iv != null, "Invalid value for IVType: " + ivType.ToString("G")); 
            cs.Write(iv, 0, iv.Length);
        } 

        cs.Write(buf, start, length);
        if (fEncrypt && modifier != null) 
        {
            cs.Write(modifier, 0, modifier.Length);
        }

        cs.FlushFinalBlock();
        byte[] paddedData = ms.ToArray(); 
        byte[] bData; 
        cs.Close();
        ReturnCryptoTransform(fEncrypt, oDesEnc, useValidationSymAlgo, useLegacyMode); 

        // DevDiv Bugs 137864: Strip Random or Hashed IV from beginning of unencrypted data
        if (!fEncrypt && createIV)
        { 
            // strip off the first bytes that were either random bits or a hash of the original data
            // either way it is always equal to the key length 
            int ivLength = (useValidationSymAlgo ? _IVLengthValidation : _IVLengthDecryption); 
            int bDataLength = paddedData.Length - ivLength;

            // valid if the data is long enough to have included the padding
            if (bDataLength >= 0)
            {
                bData = new byte[bDataLength]; 
                // copy from the padded data to non-padded buffer bData.
                // dont bother with copy if the data is entirely the padding 
                if (bDataLength > 0) 
                {
                    Buffer.BlockCopy(paddedData, ivLength, bData, 0, bDataLength); 
                }
            }
            else
            { 
                // data is not padded because it is not long enough
                bData = paddedData; 
            } 
        }
        else 
        {
            bData = paddedData;
        }

        if (!fEncrypt && modifier != null && modifier.Length > 0)
        { 
            for(int iter=0; iter<modifier.Length; iter++) 
                if (bData[bData.Length - modifier.Length + iter] != modifier[iter])
                    throw new HttpException(SR.GetString(SR.Unable_to_validate_data)); 
            byte[] bData2 = new byte[bData.Length - modifier.Length];
            Buffer.BlockCopy(bData, 0, bData2, 0, bData2.Length);
            bData = bData2;
        } 
        return bData;
    } 
}