diff --git a/src/main/scala/net/kemitix/s3thorp/S3MetaDataEnricher.scala b/src/main/scala/net/kemitix/s3thorp/S3MetaDataEnricher.scala
index 09eeec6..6ec12ac 100644
--- a/src/main/scala/net/kemitix/s3thorp/S3MetaDataEnricher.scala
+++ b/src/main/scala/net/kemitix/s3thorp/S3MetaDataEnricher.scala
@@ -1,7 +1,6 @@
 package net.kemitix.s3thorp
 
 import java.io.File
-import java.time.Instant
 
 import fs2.Stream
 import cats.effect.IO
@@ -9,11 +8,18 @@ import Main.putStrLn
 
 trait S3MetaDataEnricher extends S3Client {
 
-  def enrichWithS3MetaData: File => Stream[IO, S3MetaData] =
-    file => Stream.eval(for {
-      _ <- putStrLn(s"enrich: $file")
-      // HEAD(bucket, prefix, relative(file))
-      // create blank S3MetaData records (sealed trait?)
-    } yield S3MetaData(file, "", "", Instant.now()))
+  def generateKey(c: Config)(file: File): String = {
+    s"${c.prefix}/${c.source.toPath.relativize(file.toPath)}"
+  }
 
+  def enrichWithS3MetaData(c: Config): File => Stream[IO, S3MetaData] = {
+    val fileToString = generateKey(c)_
+    file =>
+      Stream.eval(for {
+        _ <- putStrLn(s"enrich: $file")
+        key = fileToString(file)
+        head <- IO(objectHead(c.bucket, key))
+        (hash, lastModified) = head
+      } yield S3MetaData(file, key, hash, lastModified))
+  }
 }
diff --git a/src/main/scala/net/kemitix/s3thorp/Sync.scala b/src/main/scala/net/kemitix/s3thorp/Sync.scala
index 81fb3f2..a3c8aae 100644
--- a/src/main/scala/net/kemitix/s3thorp/Sync.scala
+++ b/src/main/scala/net/kemitix/s3thorp/Sync.scala
@@ -15,7 +15,7 @@ object Sync extends LocalFileStream with S3MetaDataEnricher {
     _ <- putStrLn(s"Bucket: ${c.bucket}, Prefix: ${c.prefix}, Source: ${c.source}")
     _ <- {
       streamDirectoryPaths(c.source).flatMap(
-        enrichWithS3MetaData).flatMap(
+        enrichWithS3MetaData(c)).flatMap(
         uploadRequiredFilter).flatMap(
         performUpload).compile.drain
     }
diff --git a/src/test/scala/net/kemitix/s3thorp/S3MetaDataEnricherSuite.scala b/src/test/scala/net/kemitix/s3thorp/S3MetaDataEnricherSuite.scala
new file mode 100644
index 0000000..cd9a830
--- /dev/null
+++ b/src/test/scala/net/kemitix/s3thorp/S3MetaDataEnricherSuite.scala
@@ -0,0 +1,39 @@
+package net.kemitix.s3thorp
+
+import java.io.File
+import java.nio.file.Paths
+
+import net.kemitix.s3thorp.Sync.{Hash, LastModified}
+import org.scalatest.FunSpec
+
+class S3MetaDataEnricherSuite extends FunSpec {
+
+  new S3MetaDataEnricher {
+    describe("key generator") {
+      val path = "/root/from/here"
+      val source = Paths.get(path).toFile
+      val prefix = "prefix"
+      val config = Config("bucket", prefix, source)
+      val subject = generateKey(config)_
+
+      def resolve(subdir: String): File = {
+        source.toPath.resolve(subdir).toFile
+      }
+
+      describe("when file is within source") {
+        it("has a valid key") {
+          val subdir = "subdir"
+          assertResult(s"$prefix/$subdir")(subject(resolve(subdir)))
+        }
+      }
+
+      describe("when file is deeper within source") {
+        it("has a valid key") {
+          val subdir = "subdir/deeper/still"
+          assertResult(s"$prefix/$subdir")(subject(resolve(subdir)))
+        }
+      }
+    }
+    override def objectHead(bucket: String, key: String): (Hash, LastModified) = ???
+  }
+}