diff --git a/lib/src/main/java/im/status/keycard/applet/Metadata.java b/lib/src/main/java/im/status/keycard/applet/Metadata.java
new file mode 100644
index 0000000..eafd785
--- /dev/null
+++ b/lib/src/main/java/im/status/keycard/applet/Metadata.java
@@ -0,0 +1,106 @@
+package im.status.keycard.applet;
+
+import java.io.ByteArrayOutputStream;
+import java.nio.charset.Charset;
+import java.util.SortedSet;
+import java.util.TreeSet;
+
+public class Metadata {
+  private String cardName;
+  private SortedSet<Long> wallets;
+  
+  public static Metadata fromData(byte[] data) {
+    int version = (data[0] & 0xe0) >> 5;
+
+    if (version != 1) {
+      throw new RuntimeException("Invalid version");
+    }
+
+    int namelen = (data[0] & 0x1f);
+    int off = 1;
+
+    String cardName = new String(data, off, namelen, Charset.forName("US-ASCII"));
+    off += namelen;
+
+    SortedSet<Long> set = new TreeSet<>();
+
+    while(off < data.length) {
+      int[] start = TinyBERTLV.readNum(data, off);
+      int[] count = TinyBERTLV.readNum(data, start[1]);
+      off = count[1];
+      long s = start[0] & 0xffffffffl;
+      buildRange(set, s, (s + count[0]));
+    }
+
+    return new Metadata(cardName, set);
+  }
+
+  private static void buildRange(SortedSet<Long> set, long start, long end) {
+    for (long i = start; i <= end; i++) {
+      set.add(i);
+    }
+  }
+
+  Metadata(String cardName, SortedSet<Long> wallets) {
+    this.cardName = cardName;
+    this.wallets = wallets;
+  }
+
+  public Metadata(String cardName) {
+    this(cardName, new TreeSet<>());
+  }
+
+  public String getCardName() {
+    return cardName;
+  }
+
+  public void setCardName(String cardName) {
+    if (cardName.length() > 20) {
+      throw new IllegalArgumentException("card name too long");
+    }
+    
+    this.cardName = cardName;
+  }
+
+  public SortedSet<Long> getWallets() {
+    return wallets;
+  }
+
+  public void addWallet(long w) {
+    this.wallets.add(w);
+  }
+
+  public void removeWallet(long w) {
+    this.wallets.remove(w);
+  }
+
+  public byte[] toByteArray() {
+    ByteArrayOutputStream os = new ByteArrayOutputStream();
+    byte[] name = this.cardName.getBytes(Charset.forName("US-ASCII"));
+    os.write(0x20 | name.length);
+    os.write(name, 0, name.length);
+
+    if (wallets.isEmpty()) {
+      return os.toByteArray();
+    }
+
+    long start = wallets.first();
+    int len = 0;
+
+    for (Long w : wallets.tailSet(start + 1)) {
+      if (w == (start + len + 1)) {
+        len++;
+      } else {
+        TinyBERTLV.writeNum(os, (int) start);
+        TinyBERTLV.writeNum(os, len);
+        len = 0;
+        start = w;
+      }
+    }
+
+    TinyBERTLV.writeNum(os, (int) start);
+    TinyBERTLV.writeNum(os, len);
+
+    return os.toByteArray();
+  }
+}
diff --git a/lib/src/main/java/im/status/keycard/applet/TinyBERTLV.java b/lib/src/main/java/im/status/keycard/applet/TinyBERTLV.java
index 01cd33e..41e5183 100644
--- a/lib/src/main/java/im/status/keycard/applet/TinyBERTLV.java
+++ b/lib/src/main/java/im/status/keycard/applet/TinyBERTLV.java
@@ -1,5 +1,6 @@
 package im.status.keycard.applet;
 
+import java.io.ByteArrayOutputStream;
 import java.util.Arrays;
 
 /**
@@ -14,6 +15,57 @@ public class TinyBERTLV {
   private byte[] buffer;
   private int pos;
 
+  public static int[] readNum(byte[] buf, int off) {
+    int len = buf[off++] & 0xff;
+    int lenlen = 0;
+
+    if ((len & 0x80) == 0x80) {
+      lenlen = len & 0x7f;
+      len = readVal(buf, off, lenlen);
+    }
+
+    return new int[] {len, off + lenlen};
+  }
+
+  public static int readVal(byte[] val, int off, int len) {
+    switch (len) {
+      case 1:
+        return val[off] & 0xff;
+      case 2:
+        return ((val[off] & 0xff) << 8) | (val[off+1] & 0xff);
+      case 3:
+        return ((val[off] & 0xff) << 16) | ((val[off+1] & 0xff) << 8) | (val[off+2] & 0xff);
+      case 4:
+        return ((val[off] & 0xff) << 24) | ((val[off+1] & 0xff) << 16) | ((val[off+2] & 0xff) << 8) | (val[off+3] & 0xff);
+      default:
+        throw new IllegalArgumentException("Integers of length " + len + " are unsupported");
+    }    
+  }
+
+  public static void writeNum(ByteArrayOutputStream os, int len) {
+    if ((len & 0xff000000) != 0) {
+      os.write(0x84);
+      os.write((len & 0xff000000) >> 24);
+      os.write((len & 0x00ff0000) >> 16);
+      os.write((len & 0x0000ff00) >> 8);
+      os.write(len & 0x000000ff);
+    } else if ((len & 0x00ff0000) != 0) {
+      os.write(0x83);
+      os.write((len & 0x00ff0000) >> 16);
+      os.write((len & 0x0000ff00) >> 8);
+      os.write(len & 0x000000ff);
+    } else if ((len & 0x0000ff00) != 0) {
+      os.write(0x82);
+      os.write((len & 0x0000ff00) >> 8);
+      os.write(len & 0x000000ff);
+    } else if ((len & 0x00000080) != 0) {
+      os.write(0x81);
+      os.write(len & 0x000000ff);
+    } else {
+      os.write(len);
+    }
+  }
+
   public TinyBERTLV(byte[] buffer) {
     this.buffer = buffer;
     this.pos = 0;
@@ -64,19 +116,7 @@ public class TinyBERTLV {
    */
   public int readInt() throws IllegalArgumentException {
     byte[] val = readPrimitive(TLV_INT);
-
-    switch (val.length) {
-      case 1:
-        return val[0] & 0xff;
-      case 2:
-        return ((val[0] & 0xff) << 8) | (val[1] & 0xff);
-      case 3:
-        return ((val[0] & 0xff) << 16) | ((val[1] & 0xff) << 8) | (val[2] & 0xff);
-      case 4:
-        return ((val[0] & 0xff) << 24) | ((val[1] & 0xff) << 16) | ((val[2] & 0xff) << 8) | (val[3] & 0xff);
-      default:
-        throw new IllegalArgumentException("Integers of length " + val.length + " are unsupported");
-    }
+    return TinyBERTLV.readVal(val, 0, val.length);
   }
 
   /**
@@ -104,13 +144,9 @@ public class TinyBERTLV {
    * @return the tag
    */
   public int readLength() {
-    int len = buffer[pos++] & 0xff;
-
-    if (len == 0x81) {
-      len = buffer[pos++] & 0xff;
-    }
-
-    return len;
+    int[] len = TinyBERTLV.readNum(buffer, pos);
+    pos = len[1];
+    return len[0];
   }
 
   private void checkTag(int expected, int actual) throws IllegalArgumentException {