Create/Verify signed license files

The purpose of the class is to provide an easy way for create and verify a signed license file (or key). I am interested in any improvments / thoughts about the class.

Usage:

var signer = new LengthSigner();

// creation
var properties = new Dictionary();
properties.Add("Key1", "Value1");
properties.Add("Key2", "Value2");
var licenseFile = new LicenseFile("Me", "My Company", properties);
licenseFile.Sign(new LengthSigner());
var content = licenseFile.Serialize();
Console.WriteLine(content);
// actual content:
// ExcsNAEsVjMTFCI0BjhUMxgSMgk8TwEOKG97JHVtCXNDTHsJPEkBehMYVGVadwEyLyhJYU8wXlVDTndhBA9uNREvCA==

// unconfused content:
// 15.07.2016 00:00:00
// Me
// My Company
// Key1:Value1
// Key2:Value2
// 63

// verification
var deserializedLicenseFile = LicenseFile.Deserialize(content);
deserializedLicenseFile.Verify(new LengthSigner()); // true

LicenseFile.cs

```
public class LicenseFile
{
public LicenseFile(string licensee, string company, IDictionary properties)
: this(licensee, company, DateTime.UtcNow.Date, properties, null)
{
}

private LicenseFile(string licensee, string company, DateTime issueDate, IDictionary properties, string signature)
{
if (string.IsNullOrWhiteSpace(licensee))
throw new ArgumentException("licensee");

IssueDate = issueDate;
Licensee = licensee;
Company = string.IsNullOrWhiteSpace(company) ? "Private License" : company;
Signature = signature;
var dict = properties ?? new Dictionary();
if (dict.Keys.Any(key => key.Contains(":")))
throw new FormatException("Character ':' is not allowed as property key.");

Properties = new ReadOnlyDictionary(dict);
}

private static byte[] ConfusingBytes = new byte[] { 34, 34, 2, 4, 54, 2, 100, 3 };
public DateTime IssueDate { get; private set; }
public string Licensee { get; private set; }
public string Company { get; private set; }
private string Signature {

Just scratching on the surface - SOLID Principle

-
Interface Segregation : Why is your ISigner responsible for Signing and Verifying. From the name I would imagine it's responsibility is to Sign and not Verify.

-
Dependency Injection : In your second constructor, you create this

Properties = new ReadOnlyDictionary(dict);
why not Properties=properties

-
Arrays are always declared with the first letter as Lowercase

private static byte[] ConfusingBytes = new byte[] { 34, 34, 2, 4, 54, 2, 100, 3 };
should be

private static byte[] confusingBytes = new byte[] { 34, 34, 2, 4, 54, 2, 100, 3 };

Note you might as well use DateTime.TryParse as opposed to Try..Catch

StackExchange Code Review Q#134948, answer score: 2