diff --git a/crypto_kdf.js b/crypto_kdf.js
new file mode 100644
index 0000000..1536250
--- /dev/null
+++ b/crypto_kdf.js
@@ -0,0 +1,37 @@
+var assert = require('assert')
+var randombytes_buf = require('.').randombytes_buf
+var blake2b = require('blake2b')
+
+module.exports.crypto_kdf_PRIMITIVE = 'blake2b'
+module.exports.crypto_kdf_BYTES_MIN = 16
+module.exports.crypto_kdf_BYTES_MAX = 64
+module.exports.crypto_kdf_CONTEXTBYTES = 8
+module.exports.crypto_kdf_KEYBYTES = 64
+
+function STORE64_LE(dest, int) {
+  var mul = 1
+  var i = 0
+  dest[0] = int & 0xFF
+  while (++i < 8 && (mul *= 0x100)) {
+    dest[i] = (int / mul) & 0xFF
+  }
+}
+
+module.exports.crypto_kdf_derive_from_key = function crypto_kdf_derive_from_key (subkey, subkey_id, ctx, key) {
+  assert(subkey.length >= module.exports.crypto_kdf_BYTES_MIN, 'subkey must be')
+  assert(ctx.length >= module.exports.crypto_kdf_CONTEXTBYTES, 'context must be')
+
+  var ctx_padded = new Uint8Array(blake2b.PERSONALBYTES)
+  var salt = new Uint8Array(blake2b.SALTBYTES)
+
+  ctx_padded.set(ctx, 0, module.exports.crypto_kdf_CONTEXTBYTES)
+
+  STORE64_LE(salt, subkey_id)
+
+  blake2b(subkey.slice(0, Math.min(subkey.length, module.exports.crypto_kdf_BYTES_MAX)), [], key, salt, ctx_padded, true)
+}
+
+module.exports.crypto_kdf_keygen = function crypto_kdf_keygen (out) {
+  assert(out.length >= module.exports.crypto_kdf_KEYBYTES)
+  randombytes_buf(out, module.exports.crypto_kdf_KEYBYTES)
+}
diff --git a/index.js b/index.js
index 9e7624c..98b818f 100644
--- a/index.js
+++ b/index.js
@@ -2198,6 +2198,7 @@ sodium.crypto_sign_detached = crypto_sign_detached
 sodium.crypto_sign_verify_detached = crypto_sign_verify_detached
 
 forward(require('./crypto_generichash'))
+forward(require('./crypto_kdf'))
 
 sodium.crypto_stream_KEYBYTES = 32
 sodium.crypto_stream_NONCEBYTES = 24
diff --git a/package.json b/package.json
index dfb00de..27b279a 100644
--- a/package.json
+++ b/package.json
@@ -7,7 +7,7 @@
     "blake2b": "^1.2.0"
   },
   "devDependencies": {
-    "sodium-test": "^0.2.0"
+    "sodium-test": "^0.3.0"
   },
   "repository": {
     "type": "git",