1 files changed, 25 insertions, 0 deletions
diff --git a/openpgp/src/crypto/backend/nettle/kdf.rs b/openpgp/src/crypto/backend/nettle/kdf.rs
new file mode 100644
index 00000000..a016a3a3
--- /dev/null
+++ b/openpgp/src/crypto/backend/nettle/kdf.rs
@@ -0,0 +1,25 @@
+use nettle::{
+    kdf::hkdf,
+    hash::Sha256,
+};
+
+use crate::{
+    Result,
+    crypto::{
+        SessionKey,
+        backend::interface::Kdf,
+    },
+};
+
+impl Kdf for super::Backend {
+    fn hkdf_sha256(ikm: &SessionKey, salt: Option<&[u8]>, info: &[u8],
+                   okm: &mut SessionKey)
+                   -> Result<()>
+    {
+        assert!(okm.len() <= 255 * 32);
+        const NO_SALT: [u8; 32] = [0; 32];
+        let salt = salt.unwrap_or(&NO_SALT);
+        hkdf::<Sha256>(&ikm[..], salt, info, okm);
+        Ok(())
+    }
+}