diff --git a/network-poc/static/index.html b/network-poc/static/index.html
index ee83c0d..a91819d 100644
--- a/network-poc/static/index.html
+++ b/network-poc/static/index.html
@@ -1989,7 +1989,18 @@
             if (!card) return;
             const files = projectFiles[cardId];
 
-            // Luodaan ZIP ilman ulkoisia kirjastoja (yksinkertainen uncompressed ZIP)
+            // CRC-32 laskenta ZIP-tiedostoille
+            function crc32(bytes) {
+                let crc = 0xFFFFFFFF;
+                for (let i = 0; i < bytes.length; i++) {
+                    crc ^= bytes[i];
+                    for (let j = 0; j < 8; j++) {
+                        crc = (crc >>> 1) ^ (crc & 1 ? 0xEDB88320 : 0);
+                    }
+                }
+                return (crc ^ 0xFFFFFFFF) >>> 0;
+            }
+
             const entries = Object.entries(files);
             const parts = [];
             const centralDir = [];
@@ -1998,6 +2009,7 @@
             for (const [name, content] of entries) {
                 const nameBytes = new TextEncoder().encode(name);
                 const contentBytes = new TextEncoder().encode(content);
+                const crc = crc32(contentBytes);
 
                 // Local file header
                 const header = new Uint8Array(30 + nameBytes.length);
@@ -2005,8 +2017,9 @@
                 view.setUint32(0, 0x04034b50, true);  // Signature
                 view.setUint16(4, 20, true);           // Version needed
                 view.setUint16(8, 0, true);            // Method: store
-                view.setUint32(18, contentBytes.length, true); // Compressed size
-                view.setUint32(22, contentBytes.length, true); // Uncompressed size
+                view.setUint32(14, crc, true);         // CRC-32
+                view.setUint32(18, contentBytes.length, true);
+                view.setUint32(22, contentBytes.length, true);
                 view.setUint16(26, nameBytes.length, true);
                 header.set(nameBytes, 30);
 
@@ -2016,6 +2029,7 @@
                 cdView.setUint32(0, 0x02014b50, true);
                 cdView.setUint16(4, 20, true);
                 cdView.setUint16(6, 20, true);
+                cdView.setUint32(16, crc, true);       // CRC-32
                 cdView.setUint32(20, contentBytes.length, true);
                 cdView.setUint32(24, contentBytes.length, true);
                 cdView.setUint16(28, nameBytes.length, true);