Re-encode signature for DSA.

YubicoLabs · Dec 13, 2023 · a3b175d · a3b175d
1 parent 37299ad
commit a3b175d
Showing 1 changed file with 6 additions and 0 deletions.
diff --git a/bark_core/signatures.py b/bark_core/signatures.py
@@ -223,13 +223,19 @@ def ssh_verify_signature(
     if isinstance(key, RSAPublicKey):
         key.verify(signature, message, PKCS1v15(), h())
     elif isinstance(key, EllipticCurvePublicKey):
+        # R and S encoded as bytestrings
         r, signature = ssh_get_string(signature)
         s, signature = ssh_get_string(signature)
         signature = encode_dss_signature(
             int.from_bytes(r, "big"), int.from_bytes(s, "big")
         )
         key.verify(signature, message, ECDSA(h()))
     elif isinstance(key, DSAPublicKey):
+        # R and S encoded as 20 bytes each
+        r, s = signature[:20], signature[20:]
+        signature = encode_dss_signature(
+            int.from_bytes(r, "big"), int.from_bytes(s, "big")
+        )
         key.verify(signature, message, h())
     else:
         key.verify(signature, message)