public override string GetPassword(string username, string passwordAnswer)
{
    if (!this.EnablePasswordRetrieval)
    {
        throw new NotSupportedException(SR.GetString("Membership_PasswordRetrieval_not_supported"));
    }
    SecUtility.CheckParameter(ref username, true, true, true, 0x100, "username");
    string encodedPasswordAnswer = this.GetEncodedPasswordAnswer(username, passwordAnswer);
    SecUtility.CheckParameter(ref encodedPasswordAnswer, this.RequiresQuestionAndAnswer, this.RequiresQuestionAndAnswer, false, 0x80, "passwordAnswer");
    int passwordFormat = 0;
    int status = 0;
    string pass = this.GetPasswordFromDB(username, encodedPasswordAnswer, this.RequiresQuestionAndAnswer, out passwordFormat, out status);
    if (pass != null)
    {
        return base.UnEncodePassword(pass, passwordFormat);
    }
    string exceptionText = this.GetExceptionText(status);
    if (this.IsStatusDueToBadPassword(status))
    {
        throw new MembershipPasswordException(exceptionText);
    }
    throw new ProviderException(exceptionText);
}

 

 

Code
internal string UnEncodePassword(string pass, int passwordFormat)
{
    switch (passwordFormat)
    {
        case 0:
            return pass;

        case 1:
            throw new ProviderException(SR.GetString("Provider_can_not_decode_hashed_password"));
    }
    byte[] encodedPassword = Convert.FromBase64String(pass);
    byte[] bytes = this.DecryptPassword(encodedPassword);
    if (bytes == null)
    {
        return null;
    }
    return Encoding.Unicode.GetString(bytes, 0x10, bytes.Length - 0x10);
}