Add LD sig from little-boxes

app/ldsig.py

@@ -0,0 +1,77 @@
+import base64
+import hashlib
+import typing
+from datetime import datetime
+from functools import lru_cache
+from typing import Any
+
+from Crypto.Hash import SHA256
+from Crypto.Signature import PKCS1_v1_5
+from pyld import jsonld  # type: ignore
+
+if typing.TYPE_CHECKING:
+    from app.key import Key
+
+
+_LOADER = jsonld.requests_document_loader()
+
+
+@lru_cache(256)
+def _caching_document_loader(url: str) -> Any:
+    return _LOADER(url)
+
+
+jsonld.set_document_loader(_caching_document_loader)
+
+
+def _options_hash(doc):
+    doc = dict(doc["signature"])
+    for k in ["type", "id", "signatureValue"]:
+        if k in doc:
+            del doc[k]
+    doc["@context"] = "https://w3id.org/identity/v1"
+    normalized = jsonld.normalize(
+        doc, {"algorithm": "URDNA2015", "format": "application/nquads"}
+    )
+    h = hashlib.new("sha256")
+    h.update(normalized.encode("utf-8"))
+    return h.hexdigest()
+
+
+def _doc_hash(doc):
+    doc = dict(doc)
+    if "signature" in doc:
+        del doc["signature"]
+    normalized = jsonld.normalize(
+        doc, {"algorithm": "URDNA2015", "format": "application/nquads"}
+    )
+    h = hashlib.new("sha256")
+    h.update(normalized.encode("utf-8"))
+    return h.hexdigest()
+
+
+def verify_signature(doc, key: "Key"):
+    to_be_signed = _options_hash(doc) + _doc_hash(doc)
+    signature = doc["signature"]["signatureValue"]
+    signer = PKCS1_v1_5.new(key.pubkey or key.privkey)  # type: ignore
+    digest = SHA256.new()
+    digest.update(to_be_signed.encode("utf-8"))
+    return signer.verify(digest, base64.b64decode(signature))  # type: ignore
+
+
+def generate_signature(doc, key: "Key"):
+    options = {
+        "type": "RsaSignature2017",
+        "creator": doc["actor"] + "#main-key",
+        "created": datetime.utcnow().replace(microsecond=0).isoformat() + "Z",
+    }
+    doc["signature"] = options
+    to_be_signed = _options_hash(doc) + _doc_hash(doc)
+    if not key.privkey:
+        raise ValueError(f"missing privkey on key {key!r}")
+
+    signer = PKCS1_v1_5.new(key.privkey)
+    digest = SHA256.new()
+    digest.update(to_be_signed.encode("utf-8"))
+    sig = base64.b64encode(signer.sign(digest))  # type: ignore
+    options["signatureValue"] = sig.decode("utf-8")