Allow the verification of signatures and events

Added the methods:
- Event#verify_signature
- Crypto#check_sig!
- Crypto#valid_sig?
- Crypto#sign_message

Fixed a primitive obsession by introducing a Signature class to ensure that signatures are valid Nostr signatures.

sig/nostr/crypto.rbs

@@ -7,6 +7,9 @@ module Nostr
     def encrypt_text: (PrivateKey, PublicKey, String) -> String
     def decrypt_text: (PrivateKey, PublicKey, String) -> String
     def sign_event: (Event, PrivateKey) -> Event
+    def sign_message: (String, PrivateKey) -> Signature
+    def valid_sig?: (String, PublicKey, Signature) -> bool
+    def check_sig!: (String, PublicKey, Signature) -> bool
 
     private
 

sig/nostr/errors/invalid_signature_format_error.rbs

@@ -0,0 +1,5 @@
+module Nostr
+  class InvalidSignatureFormatError < SignatureValidationError
+    def initialize: -> void
+  end
+end

sig/nostr/errors/invalid_signature_length_error.rbs

@@ -0,0 +1,5 @@
+module Nostr
+  class InvalidSignatureLengthError < SignatureValidationError
+    def initialize: -> void
+  end
+end

sig/nostr/errors/invalid_signature_type_error.rbs

@@ -0,0 +1,5 @@
+module Nostr
+  class InvalidSignatureTypeError < SignatureValidationError
+    def initialize: -> void
+  end
+end

sig/nostr/errors/signature_validation_error.rbs

@@ -0,0 +1,4 @@
+module Nostr
+  class SignatureValidationError < Error
+  end
+end

sig/nostr/event.rbs

@@ -6,7 +6,7 @@ module Nostr
     attr_reader tags: Array[Array[String]]
     attr_reader content: String
     attr_accessor id: String?|nil
-    attr_accessor sig: String?|nil
+    attr_accessor sig: Signature?
 
     def initialize: (
       pubkey: PublicKey,
@@ -15,7 +15,7 @@ module Nostr
       ?created_at: Integer,
       ?tags: Array[Array[String]],
       ?id: String|nil,
-      ?sig: String|nil
+      ?sig: Signature?
     ) -> void
 
     def serialize: -> [Integer, String, Integer, Integer, Array[Array[String]], String]
@@ -32,6 +32,7 @@ module Nostr
     def ==: (Event other) -> bool
 
     def sign:(PrivateKey) -> Event
+    def verify_signature: -> bool
 
     def add_event_reference: (String) -> Array[Array[String]]
     def add_pubkey_reference: (PublicKey) -> Array[Array[String]]

sig/nostr/signature.rbs

@@ -0,0 +1,14 @@
+module Nostr
+  class Signature < String
+    FORMAT: Regexp
+    LENGTH: int
+
+    def initialize: (String) -> void
+
+    private
+
+    attr_reader hex_value: String
+
+    def validate: (String) -> nil
+  end
+end