Added a method to change the password

Encrypter Tests/EncrypterTests.cs

@@ -99,7 +99,7 @@ namespace Encrypter_Tests
         }
 
         [Test]
-        public async Task TestChangedPassword()
+        public async Task TestAlteredPassword()
         {
             var message = "This is a test with umlauts äüö.";
             var password1 = "password!";
@@ -164,5 +164,41 @@ namespace Encrypter_Tests
                 Assert.That(true);
             }
         }
+
+        [Test]
+        public async Task TestChangedPasswordBehaviour()
+        {
+            var message = "This is a test with umlauts äüö.";
+            var previousPassword = "test password";
+            var newPassword = "test password!!!";
+            var iterations = 1_000;
+
+            var previousEncryptedData = await CryptoProcessor.EncryptString(message, previousPassword, iterations);
+            var reEncryptedData = await CryptoProcessor.ChangePassword(previousEncryptedData, previousPassword, newPassword, iterations);
+            Assert.That(previousEncryptedData, Is.Not.EqualTo(reEncryptedData));
+
+            var decryptedMessage = await CryptoProcessor.DecryptString(reEncryptedData, newPassword, iterations);
+            Assert.That(decryptedMessage, Is.EqualTo(message));
+
+            try
+            {
+                var decryptedMessage2 = await CryptoProcessor.DecryptString(reEncryptedData, previousPassword, iterations);
+                Assert.Fail("Should not be reached!");
+            }
+            catch (CryptographicException e)
+            {
+                Assert.That(true);
+            }
+
+            try
+            {
+                var decryptedMessage2 = await CryptoProcessor.DecryptString(previousEncryptedData, newPassword, iterations);
+                Assert.Fail("Should not be reached!");
+            }
+            catch (CryptographicException e)
+            {
+                Assert.That(true);
+            }
+        }
     }
 }

Encrypter/CryptoProcessor.cs

@@ -176,5 +176,22 @@ namespace Encrypter
             // Encrypt the data with the new settings:
             return await CryptoProcessor.EncryptString(decryptedData, password, upgradedIterations);
         }
+
+        /// <summary>
+        /// Changes the password of the encryption.
+        /// </summary>
+        /// <param name="encryptedDataBeforeChange">With the previous password encrypted data.</param>
+        /// <param name="previousPassword">The previous password.</param>
+        /// <param name="newPassword">The new password.</param>
+        /// <param name="iterations">The used iterations.</param>
+        /// <returns>The re-encrypted data.</returns>
+        public static async Task<string> ChangePassword(string encryptedDataBeforeChange, string previousPassword, string newPassword, int iterations = ITERATIONS_YEAR_2020)
+        {
+            // Decrypt the data with the previous settings:
+            var decryptedData = await CryptoProcessor.DecryptString(encryptedDataBeforeChange, previousPassword, iterations);
+
+            // Encrypt the data with the new settings:
+            return await CryptoProcessor.EncryptString(decryptedData, newPassword, iterations);
+        }
     }
 }

Encrypter/Encrypter.xml

@@ -45,6 +45,16 @@
             <param name="upgradedIterations">The upgraded number of iterations.</param>
             <returns>The re-encrypted data.</returns>
         </member>
+        <member name="M:Encrypter.CryptoProcessor.ChangePassword(System.String,System.String,System.String,System.Int32)">
+            <summary>
+            Changes the password of the encryption.
+            </summary>
+            <param name="encryptedDataBeforeChange">With the previous password encrypted data.</param>
+            <param name="previousPassword">The previous password.</param>
+            <param name="newPassword">The new password.</param>
+            <param name="iterations">The used iterations.</param>
+            <returns>The re-encrypted data.</returns>
+        </member>
         <member name="M:Encrypter.Extensions.Encrypt(System.String,System.String)">
             <summary>
             Encrypts this string by means of AES. The result gets base64 encoded.