gistfile1.cs

public class PasswordsMustMatchAttribute : ValidationAttribute
{
    protected override ValidationResult IsValid(
        object value, ValidationContext validationContext)
    {
        var model = validationContext.ObjectInstance as Person;
        if (model.Password == model.PasswordConfirm)
        {
            return ValidationResult.Success;
        }

        return new ValidationResult(
            "Password and Password Confirmation must match",
            new string[] { "Password", "PasswordConfirm" });
    }
}