Add secret key encrypt_easy.

spec/cox/secret_key_spec.cr

@@ -0,0 +1,16 @@
+require "../spec_helper"
+
+describe Cox::SecretKey do
+  it "encrypts/decrypts" do
+    key = Cox::SecretKey.random
+
+    message = "foobar"
+    encrypted, nonce = key.encrypt_easy message
+    decrypted = key.decrypt_easy encrypted, nonce
+    message.should eq String.new(decrypted)
+
+    expect_raises(Cox::DecryptionFailed) do
+      key.decrypt_easy "badmsgbadmsgbadmsgbadmsgbadmsg".to_slice, nonce
+    end
+  end
+end

src/cox/lib_sodium.cr

@@ -33,6 +33,22 @@ module Cox
     KDF_CONTEXT_BYTES = crypto_kdf_contextbytes()
     PWHASH_STR_BYTES  = crypto_pwhash_strbytes()
 
+    fun crypto_secretbox_easy(
+      output               : Pointer(LibC::UChar),
+      data                 : Pointer(LibC::UChar),
+      data_size            : LibC::ULongLong,
+      nonce                : Pointer(LibC::UChar),
+      key : Pointer(LibC::UChar),
+    ) : LibC::Int
+
+    fun crypto_secretbox_open_easy(
+      output               : Pointer(LibC::UChar),
+      data                 : Pointer(LibC::UChar),
+      data_size            : LibC::ULongLong,
+      nonce                : Pointer(LibC::UChar),
+      key : Pointer(LibC::UChar),
+    ) : LibC::Int
+
     fun crypto_box_keypair(
       public_key_output : Pointer(LibC::UChar),
       secret_key_output : Pointer(LibC::UChar)

src/cox/secret_key.cr

@@ -11,5 +11,43 @@ module Cox
         raise ArgumentError.new("Secret key must be #{KEY_LENGTH} bytes, got #{bytes.bytesize}")
       end
     end
+
+    def self.random
+      new Random::Secure.random_bytes(KEY_LENGTH)
+    end
+
+    def encrypt_easy(data)
+      encrypt_easy data.to_slice
+    end
+
+    def encrypt_easy(data, nonce : Nonce)
+      encrypt_easy data.to_slice, nonce
+    end
+
+    def encrypt_easy(data : Bytes)
+      nonce = Nonce.new
+      output = encrypt_easy data, nonce
+      {output, nonce}
+    end
+
+    def encrypt_easy(data : Bytes, nonce : Nonce) : Bytes
+      output = Bytes.new(data.bytesize + LibSodium::MAC_BYTES)
+      if LibSodium.crypto_secretbox_easy(output, data, data.bytesize, nonce.pointer, @bytes) != 0
+        raise Cox::Error.new("crypto_secretbox_easy")
+      end
+      output
+    end
+
+    def decrypt_easy(data : Bytes, nonce : Nonce) : Bytes
+      output_size = data.bytesize - LibSodium::MAC_BYTES
+      raise Cox::DecryptionFailed.new("encrypted data too small #{data.bytesize}") if output_size <= 0
+      output = Bytes.new output_size
+      if LibSodium.crypto_secretbox_open_easy(output, data, data.bytesize, nonce.pointer, @bytes) != 0
+        raise Cox::DecryptionFailed.new("crypto_secretbox_easy")
+      end
+      output
+    end
+
+    # TODO: encrypt_detached
   end
 end