Added password change for streams

Encrypter Tests/EncrypterTests.cs

@@ -279,6 +279,93 @@ public async Task TestChangedPasswordBehaviour()
             }
         }
 
+        [Test]
+        public async Task TestChangedPasswordBehaviourStreaming()
+        {
+            var tempFileInput = Path.GetTempFileName();
+            var tempFileEncryptedPrevious = Path.GetTempFileName();
+            var tempFileReEncrypted = Path.GetTempFileName();
+            var tempFileDecrypted = Path.GetTempFileName();
+
+            try
+            {
+                var message = "This is a test with umlauts äüö.";
+                await File.WriteAllTextAsync(tempFileInput, message);
+
+                var passwordPrevious = "test password";
+                var passwordNext = "better password";
+                var iterations = 1_000;
+
+                await using (var outputStream = File.OpenWrite(tempFileEncryptedPrevious))
+                {
+                    await using var inputStream = File.OpenRead(tempFileInput);
+                    await CryptoProcessor.Encrypt(inputStream, outputStream, passwordPrevious, iterations);
+                }
+
+                await using (var outputStream = File.OpenWrite(tempFileReEncrypted))
+                {
+                    await using var inputStream = File.OpenRead(tempFileEncryptedPrevious);
+                    await CryptoProcessor.ChangePassword(inputStream, outputStream, passwordPrevious, passwordNext, iterations);
+                }
+
+                Assert.That(await File.ReadAllBytesAsync(tempFileEncryptedPrevious), Is.Not.EqualTo(await File.ReadAllBytesAsync(tempFileReEncrypted)));
+
+                await using (var outputStream = File.OpenWrite(tempFileDecrypted))
+                {
+                    await using var inputStream = File.OpenRead(tempFileReEncrypted);
+                    await CryptoProcessor.Decrypt(inputStream, outputStream, passwordNext, iterations);
+                }
+
+                Assert.That(await File.ReadAllTextAsync(tempFileDecrypted), Is.EqualTo(message));
+
+                try
+                {
+                    await using var tempBuffer = new MemoryStream();
+                    await using var inputStream = File.OpenRead(tempFileReEncrypted);
+                    await CryptoProcessor.Decrypt(inputStream, tempBuffer, passwordPrevious, iterations);
+                    Assert.Fail("Should not be reached!");
+                }
+                catch (CryptographicException e)
+                {
+                    Assert.That(true);
+                }
+            }
+            finally
+            {
+                try
+                {
+                    File.Delete(tempFileInput);
+                }
+                catch
+                {
+                }
+
+                try
+                {
+                    File.Delete(tempFileDecrypted);
+                }
+                catch
+                {
+                }
+
+                try
+                {
+                    File.Delete(tempFileEncryptedPrevious);
+                }
+                catch
+                {
+                }
+
+                try
+                {
+                    File.Delete(tempFileReEncrypted);
+                }
+                catch
+                {
+                }
+            }
+        }
+
         [Test]
         public async Task TestSimpleStream()
         {

Encrypter/CryptoProcessor.cs

@@ -374,5 +374,44 @@ public static async Task<string> ChangePassword(string encryptedDataBeforeChange
             // Encrypt the data with the new settings:
             return await CryptoProcessor.Encrypt(decryptedData, newPassword, iterations);
         }
+
+        /// <summary>
+        /// Changes the password of the encryption. In order to re-encrypt the stream, a temporary file
+        /// gets used. When the returned task is finished, the re-encryption is done as well.
+        /// </summary>
+        /// <param name="encryptedInput">With the previous password encrypted data.</param>
+        /// <param name="reEncryptedOutput">The re-encrypted data.</param>
+        /// <param name="previousPassword">The previous password.</param>
+        /// <param name="newPassword">The new password.</param>
+        /// <param name="iterations">The used iterations.</param>
+        public static async Task ChangePassword(Stream encryptedInput, Stream reEncryptedOutput, string previousPassword, string newPassword, int iterations = ITERATIONS_YEAR_2020)
+        {
+            var tempFileCache = Path.GetTempFileName();
+
+            try
+            {
+                await using (var tempCacheStream = File.OpenWrite(tempFileCache))
+                {
+                    // Decrypt the data with the previous settings:
+                    await Decrypt(encryptedInput, tempCacheStream, previousPassword, iterations);
+                }
+
+                await using (var tempCacheStream = File.OpenRead(tempFileCache))
+                {
+                    // Encrypt the data with the new settings:
+                    await Encrypt(tempCacheStream, reEncryptedOutput, newPassword, iterations);
+                }
+            }
+            finally
+            {
+                try
+                {
+                    File.Delete(tempFileCache);
+                }
+                catch
+                {
+                }
+            }
+        }
     }
 }