diff --git a/httpclient5-cache/src/main/java/org/apache/hc/client5/http/impl/cache/BasicIdGenerator.java b/httpclient5-cache/src/main/java/org/apache/hc/client5/http/impl/cache/BasicIdGenerator.java
deleted file mode 100644
index d81b66e19..000000000
--- a/httpclient5-cache/src/main/java/org/apache/hc/client5/http/impl/cache/BasicIdGenerator.java
+++ /dev/null
@@ -1,90 +0,0 @@
-/*
- * ====================================================================
- * Licensed to the Apache Software Foundation (ASF) under one
- * or more contributor license agreements.  See the NOTICE file
- * distributed with this work for additional information
- * regarding copyright ownership.  The ASF licenses this file
- * to you under the Apache License, Version 2.0 (the
- * "License"); you may not use this file except in compliance
- * with the License.  You may obtain a copy of the License at
- *
- *   http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing,
- * software distributed under the License is distributed on an
- * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
- * KIND, either express or implied.  See the License for the
- * specific language governing permissions and limitations
- * under the License.
- * ====================================================================
- *
- * This software consists of voluntary contributions made by many
- * individuals on behalf of the Apache Software Foundation.  For more
- * information on the Apache Software Foundation, please see
- * <http://www.apache.org/>.
- *
- */
-package org.apache.hc.client5.http.impl.cache;
-
-import java.net.InetAddress;
-import java.net.UnknownHostException;
-import java.security.NoSuchAlgorithmException;
-import java.security.SecureRandom;
-import java.util.Formatter;
-import java.util.Locale;
-import java.util.concurrent.locks.ReentrantLock;
-
-/**
- * Should produce reasonably unique tokens.
- */
-class BasicIdGenerator {
-
-    private final String hostname;
-    private final SecureRandom rnd;
-
-    private long count;
-
-    private final ReentrantLock lock;
-
-    public BasicIdGenerator() {
-        super();
-        String hostname;
-        try {
-            hostname = InetAddress.getLocalHost().getHostName();
-        } catch (final UnknownHostException ex) {
-            hostname = "localhost";
-        }
-        this.hostname = hostname;
-        try {
-            this.rnd = SecureRandom.getInstance("SHA1PRNG");
-        } catch (final NoSuchAlgorithmException ex) {
-            throw new Error(ex);
-        }
-        this.rnd.setSeed(System.currentTimeMillis());
-        this.lock = new ReentrantLock();
-    }
-
-    public void generate(final StringBuilder buffer) {
-        lock.lock();
-        try {
-            this.count++;
-            final int rndnum = this.rnd.nextInt();
-            buffer.append(System.currentTimeMillis());
-            buffer.append('.');
-            try (Formatter formatter = new Formatter(buffer, Locale.ROOT)) {
-                formatter.format("%1$016x-%2$08x", this.count, rndnum);
-            }
-            buffer.append('.');
-            buffer.append(this.hostname);
-        } finally {
-            lock.unlock();
-        }
-    }
-
-    public String generate() {
-        final StringBuilder buffer = new StringBuilder();
-        generate(buffer);
-        return buffer.toString();
-    }
-
-}
diff --git a/httpclient5-cache/src/main/java/org/apache/hc/client5/http/impl/cache/FileResourceFactory.java b/httpclient5-cache/src/main/java/org/apache/hc/client5/http/impl/cache/FileResourceFactory.java
index 22d2cae1d..e0842c992 100644
--- a/httpclient5-cache/src/main/java/org/apache/hc/client5/http/impl/cache/FileResourceFactory.java
+++ b/httpclient5-cache/src/main/java/org/apache/hc/client5/http/impl/cache/FileResourceFactory.java
@@ -29,13 +29,17 @@ package org.apache.hc.client5.http.impl.cache;
 import java.io.File;
 import java.io.FileOutputStream;
 import java.io.IOException;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
 
 import org.apache.hc.client5.http.cache.Resource;
 import org.apache.hc.client5.http.cache.ResourceFactory;
 import org.apache.hc.client5.http.cache.ResourceIOException;
 import org.apache.hc.core5.annotation.Contract;
 import org.apache.hc.core5.annotation.ThreadingBehavior;
+import org.apache.hc.core5.net.PercentCodec;
 import org.apache.hc.core5.util.Args;
+import org.apache.hc.core5.util.TextUtils;
 
 /**
  * Generates {@link Resource} instances whose body is stored in a temporary file.
@@ -46,37 +50,44 @@ import org.apache.hc.core5.util.Args;
 public class FileResourceFactory implements ResourceFactory {
 
     private final File cacheDir;
-    private final BasicIdGenerator idgen;
 
     public FileResourceFactory(final File cacheDir) {
         super();
         this.cacheDir = cacheDir;
-        this.idgen = new BasicIdGenerator();
     }
 
-    private File generateUniqueCacheFile(final String requestId) {
-        final StringBuilder buffer = new StringBuilder();
-        this.idgen.generate(buffer);
-        buffer.append('.');
-        final int len = Math.min(requestId.length(), 100);
-        for (int i = 0; i < len; i++) {
-            final char ch = requestId.charAt(i);
-            if (Character.isLetterOrDigit(ch) || ch == '.') {
-                buffer.append(ch);
-            } else {
-                buffer.append('-');
+    static String generateUniqueCacheFileName(final String requestId, final String eTag, final byte[] content, final int off, final int len) {
+        final StringBuilder buf = new StringBuilder();
+        if (eTag != null) {
+            PercentCodec.RFC3986.encode(buf, eTag);
+            buf.append('@');
+        } else if (content != null) {
+            final MessageDigest sha256;
+            try {
+                sha256 = MessageDigest.getInstance("SHA-256");
+            } catch (final NoSuchAlgorithmException ex) {
+                throw new IllegalStateException(ex);
             }
+            sha256.update(content, off, len);
+            buf.append(TextUtils.toHexString(sha256.digest()));
+            buf.append('@');
         }
-        return new File(this.cacheDir, buffer.toString());
+        PercentCodec.RFC3986.encode(buf, requestId);
+        return buf.toString();
     }
 
+    /**
+     * @since 5.4
+     */
     @Override
     public Resource generate(
             final String requestId,
+            final String eTag,
             final byte[] content, final int off, final int len) throws ResourceIOException {
         Args.notNull(requestId, "Request id");
-        final File file = generateUniqueCacheFile(requestId);
-        try (FileOutputStream outStream = new FileOutputStream(file)) {
+        final String filename = generateUniqueCacheFileName(requestId, eTag, content, off, len);
+        final File file = new File(cacheDir, filename);
+        try (FileOutputStream outStream = new FileOutputStream(file, false)) {
             if (content != null) {
                 outStream.write(content, off, len);
             }
@@ -86,10 +97,22 @@ public class FileResourceFactory implements ResourceFactory {
         return new FileResource(file);
     }
 
+    @Override
+    public Resource generate(final String requestId, final byte[] content, final int off, final int len) throws ResourceIOException {
+        if (content != null) {
+            return generate(requestId, null, content, off, len);
+        } else {
+            return generate(requestId, null, null, 0, 0);
+        }
+    }
+
     @Override
     public Resource generate(final String requestId, final byte[] content) throws ResourceIOException {
-        Args.notNull(content, "Content");
-        return generate(requestId, content, 0, content.length);
+        if (content != null) {
+            return generate(requestId, null, content, 0, content.length);
+        } else {
+            return generate(requestId, null, null, 0, 0);
+        }
     }
 
     /**
diff --git a/httpclient5-cache/src/test/java/org/apache/hc/client5/http/impl/cache/TestFileResourceFactory.java b/httpclient5-cache/src/test/java/org/apache/hc/client5/http/impl/cache/TestFileResourceFactory.java
new file mode 100644
index 000000000..952f75712
--- /dev/null
+++ b/httpclient5-cache/src/test/java/org/apache/hc/client5/http/impl/cache/TestFileResourceFactory.java
@@ -0,0 +1,69 @@
+/*
+ * ====================================================================
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ * ====================================================================
+ *
+ * This software consists of voluntary contributions made by many
+ * individuals on behalf of the Apache Software Foundation.  For more
+ * information on the Apache Software Foundation, please see
+ * <http://www.apache.org/>.
+ *
+ */
+package org.apache.hc.client5.http.impl.cache;
+
+
+import java.net.URI;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+public class TestFileResourceFactory {
+
+    CacheKeyGenerator keyGenerator;
+
+    @BeforeEach
+    public void setUp() {
+        keyGenerator = new CacheKeyGenerator();
+    }
+
+    @Test
+    public void testViaValueLookup() throws Exception {
+        final String requestId = keyGenerator.generateKey(new URI("http://localhost/stuff"));
+
+        Assertions.assertEquals(
+                "blah%20blah@http%3A%2F%2Flocalhost%3A80%2Fstuff",
+                FileResourceFactory.generateUniqueCacheFileName(requestId, "blah blah", null, 0, 0));
+        Assertions.assertEquals(
+                "blah-blah@http%3A%2F%2Flocalhost%3A80%2Fstuff",
+                FileResourceFactory.generateUniqueCacheFileName(requestId, "blah-blah", null, 0, 0));
+        Assertions.assertEquals(
+                "blah%40blah@http%3A%2F%2Flocalhost%3A80%2Fstuff",
+                FileResourceFactory.generateUniqueCacheFileName(requestId, "blah@blah", null, 0, 0));
+        Assertions.assertEquals(
+                "039058c6f2c0cb492c533b0a4d14ef77cc0f78abccced5287d84a1a2011cfb81@http%3A%2F%2Flocalhost%3A80%2Fstuff",
+                FileResourceFactory.generateUniqueCacheFileName(requestId, null, new byte[]{1, 2, 3}, 0, 3));
+        Assertions.assertEquals(
+                "039058c6f2c0cb492c533b0a4d14ef77cc0f78abccced5287d84a1a2011cfb81@http%3A%2F%2Flocalhost%3A80%2Fstuff",
+                FileResourceFactory.generateUniqueCacheFileName(requestId, null, new byte[]{1, 2, 3, 4, 5}, 0, 3));
+        Assertions.assertEquals(
+                "http%3A%2F%2Flocalhost%3A80%2Fstuff",
+                FileResourceFactory.generateUniqueCacheFileName(requestId, null, null, 0, 0));
+    }
+
+}