diff --git a/src/main/java/ru/serega6531/packmate/service/PatternMatcher.java b/src/main/java/ru/serega6531/packmate/service/PatternMatcher.java
index dd01439..eba7f82 100644
--- a/src/main/java/ru/serega6531/packmate/service/PatternMatcher.java
+++ b/src/main/java/ru/serega6531/packmate/service/PatternMatcher.java
@@ -1,14 +1,15 @@
 package ru.serega6531.packmate.service;
 
 import lombok.SneakyThrows;
-import org.apache.commons.lang3.StringUtils;
 import org.springframework.security.crypto.codec.Hex;
 import ru.serega6531.packmate.model.FoundPattern;
 import ru.serega6531.packmate.model.Pattern;
 import ru.serega6531.packmate.utils.KMPByteSearcher;
+import ru.serega6531.packmate.utils.KMPStringSearcher;
 
 import java.io.ByteArrayInputStream;
 import java.io.InputStream;
+import java.io.StringReader;
 import java.util.*;
 import java.util.regex.Matcher;
 
@@ -57,24 +58,23 @@ public class PatternMatcher {
     }
 
     private void matchSubstring(Pattern pattern) {
-        int startSearch = 0;
         final String value = pattern.getValue();
+        KMPStringSearcher searcher = new KMPStringSearcher(value.toCharArray());
+        StringReader reader = new StringReader(content);
 
         while (true) {
-            int start = StringUtils.indexOfIgnoreCase(content, value, startSearch);
+            int end = searcher.search(reader) - 1;
 
-            if (start == -1) {
+            if (end < 0) {
                 return;
             }
 
-            int end = start + value.length() - 1;
+            int start = end - value.length() + 1;
             addIfPossible(FoundPattern.builder()
                     .patternId(pattern.getId())
                     .startPosition(start)
                     .endPosition(end)
                     .build());
-
-            startSearch = end + 1;
         }
     }
 
diff --git a/src/main/java/ru/serega6531/packmate/utils/KMPStringSearcher.java b/src/main/java/ru/serega6531/packmate/utils/KMPStringSearcher.java
new file mode 100644
index 0000000..c0d01d0
--- /dev/null
+++ b/src/main/java/ru/serega6531/packmate/utils/KMPStringSearcher.java
@@ -0,0 +1,62 @@
+package ru.serega6531.packmate.utils;
+
+import lombok.SneakyThrows;
+
+import java.io.StringReader;
+
+/**
+ * Based on <a href="https://github.com/twitter/elephant-bird/blob/master/core/src/main/java/com/twitter/elephantbird/util/StreamSearcher.java">StreamSearcher</a>
+ */
+public class KMPStringSearcher {
+
+    private char[] pattern;
+    private int[] borders;
+    private int lastEnd = 0;
+
+    public KMPStringSearcher(char[] pattern) {
+        setPattern(pattern);
+    }
+
+    public void setPattern(char[] pattern) {
+        this.pattern = pattern;
+        this.borders = new int[this.pattern.length + 1];
+        preProcess();
+    }
+
+    @SneakyThrows
+    public int search(StringReader reader) {
+        int bytesRead = 0;
+
+        int b;
+        int j = 0;
+
+        while ((b = reader.read()) != -1) {
+            bytesRead++;
+
+            while (j >= 0 && (char)b != pattern[j]) {
+                j = borders[j];
+            }
+            ++j;
+
+            if (j == pattern.length) {
+                lastEnd += bytesRead;
+                return lastEnd;
+            }
+        }
+
+        return -1;
+    }
+
+    private void preProcess() {
+        int i = 0;
+        int j = -1;
+        borders[i] = j;
+        while (i < pattern.length) {
+            while (j >= 0 && pattern[i] != pattern[j]) {
+                j = borders[j];
+            }
+            borders[++i] = ++j;
+        }
+    }
+
+}