public class LocalPasswordModel
{
    [Required]
    [DataType(DataType.Password)]
    [Display(Name = "Current password")]
    public string OldPassword { get; set; }

    [Required]
    [StringLength(100, ErrorMessage = "The {0} must be at least {2} characters long.", MinimumLength = 6)]
    [DataType(DataType.Password)]
    [Display(Name = "New password")]
    public string NewPassword { get; set; }

    [DataType(DataType.Password)]
    [Display(Name = "Confirm new password")]
    [Compare("NewPassword", ErrorMessage = "The new password and confirmation password do not match.")]
    public string ConfirmPassword { get; set; }
}

ErrorMessage = "The {0} must be at least {2} characters long."

{0} Property name
{1} Maximum length
{2} Minimum length

public override string FormatErrorMessage(string name)
{
    EnsureLegalLengths();
    string format = ((this.MinimumLength != 0) && !base.CustomErrorMessageSet) ? DataAnnotationsResources.StringLengthAttribute_ValidationErrorIncludingMinimum : base.ErrorMessageString;
    return String.Format(CultureInfo.CurrentCulture, format, new object[] { name, MaximumLength, MinimumLength });
}