diff --git a/fints4javaLib/src/main/kotlin/net/dankito/fints/messages/Nachrichtenteil.kt b/fints4javaLib/src/main/kotlin/net/dankito/fints/messages/Nachrichtenteil.kt
index 9d39881e..9aff09ef 100644
--- a/fints4javaLib/src/main/kotlin/net/dankito/fints/messages/Nachrichtenteil.kt
+++ b/fints4javaLib/src/main/kotlin/net/dankito/fints/messages/Nachrichtenteil.kt
@@ -1,8 +1,28 @@
 package net.dankito.fints.messages
 
+import net.dankito.fints.util.MessageUtils
 
-abstract class Nachrichtenteil {
+
+abstract class Nachrichtenteil(protected val messageUtils: MessageUtils = MessageUtils()) {
 
     abstract fun format(): String
 
+
+    open fun maskMessagePart(messagePart: String, separator: String): String {
+
+        var maskedMessagePart = messagePart
+        val binaryDataRanges = messageUtils.findBinaryDataRanges(messagePart)
+
+        val unmaskedMaskingCharacterIndices = messageUtils.findSeparatorIndices(maskedMessagePart, Separators.MaskingCharacter, binaryDataRanges)
+            .filter { messageUtils.doesNotMaskSeparatorOrMaskingCharacter(it, maskedMessagePart) }
+
+        maskedMessagePart = messageUtils
+            .maskCharacterAtIndices(maskedMessagePart, Separators.MaskingCharacter, unmaskedMaskingCharacterIndices)
+
+
+        val separatorIndices = messageUtils.findSeparatorIndices(maskedMessagePart, separator, binaryDataRanges)
+
+        return messageUtils.maskCharacterAtIndices(maskedMessagePart, separator, separatorIndices)
+    }
+
 }
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diff --git a/fints4javaLib/src/main/kotlin/net/dankito/fints/messages/Separators.kt b/fints4javaLib/src/main/kotlin/net/dankito/fints/messages/Separators.kt
index 783c182a..003f235d 100644
--- a/fints4javaLib/src/main/kotlin/net/dankito/fints/messages/Separators.kt
+++ b/fints4javaLib/src/main/kotlin/net/dankito/fints/messages/Separators.kt
@@ -11,6 +11,10 @@ class Separators {
         const val DataElementsSeparator = ":"
 
         const val MaskingCharacter = "?"
+
+        val AllSeparators = listOf(DataElementsSeparator, DataElementGroupsSeparator, SegmentSeparator)
+
+        val AllSeparatorsAndMaskingCharacter = listOf(*AllSeparators.toTypedArray(), MaskingCharacter)
     }
 
 }
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diff --git a/fints4javaLib/src/main/kotlin/net/dankito/fints/messages/datenelemente/basisformate/TextDatenelement.kt b/fints4javaLib/src/main/kotlin/net/dankito/fints/messages/datenelemente/basisformate/TextDatenelement.kt
index ab240730..04ad4da0 100644
--- a/fints4javaLib/src/main/kotlin/net/dankito/fints/messages/datenelemente/basisformate/TextDatenelement.kt
+++ b/fints4javaLib/src/main/kotlin/net/dankito/fints/messages/datenelemente/basisformate/TextDatenelement.kt
@@ -2,6 +2,7 @@ package net.dankito.fints.messages.datenelemente.basisformate
 
 import net.dankito.fints.messages.Existenzstatus
 import net.dankito.fints.messages.HbciCharset
+import net.dankito.fints.messages.Separators
 import net.dankito.fints.messages.datenelemente.Datenelement
 
 
@@ -24,7 +25,7 @@ abstract class TextDatenelement(val value: String?, existenzstatus: Existenzstat
     }
 
     protected open fun formatValue(value: String): String {
-        return value // may overwritten in sub classes
+        return maskMessagePart(value, Separators.DataElementsSeparator) // may overwritten in sub classes
     }
 
 
diff --git a/fints4javaLib/src/main/kotlin/net/dankito/fints/util/MessageUtils.kt b/fints4javaLib/src/main/kotlin/net/dankito/fints/util/MessageUtils.kt
index e28182c9..cd7f5f5d 100644
--- a/fints4javaLib/src/main/kotlin/net/dankito/fints/util/MessageUtils.kt
+++ b/fints4javaLib/src/main/kotlin/net/dankito/fints/util/MessageUtils.kt
@@ -63,6 +63,16 @@ open class MessageUtils {
         return false
     }
 
+    open fun doesNotMaskSeparatorOrMaskingCharacter(maskingCharacterIndex: Int, messagePart: String): Boolean {
+        if (maskingCharacterIndex < messagePart.length - 1) {
+            val nextCharacter = messagePart[maskingCharacterIndex + 1]
+
+            return Separators.AllSeparatorsAndMaskingCharacter.contains(nextCharacter.toString()) == false
+        }
+
+        return true
+    }
+
     open fun isInRange(index: Int, ranges: List<IntRange>): Boolean {
         for (range in ranges) {
             if (range.contains(index)) {
@@ -73,4 +83,15 @@ open class MessageUtils {
         return false
     }
 
+    open fun maskCharacterAtIndices(unmaskedString: String, unmaskedCharacter: String, indices: List<Int>): String {
+        var maskedString = unmaskedString
+
+        indices.sortedDescending().forEach { index ->
+            maskedString = maskedString.replaceRange(index, index + 1, Separators.MaskingCharacter + unmaskedCharacter
+            )
+        }
+
+        return maskedString
+    }
+
 }
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