Squashed 'bip-0352/secp256k1lab/' content from commit 44dc4bd

git-subtree-dir: bip-0352/secp256k1lab
git-subtree-split: 44dc4bd893b8f03e621585e3bf255253e0e0fbfb

src/secp256k1lab/util.py

@@ -0,0 +1,24 @@
+import hashlib
+
+
+# This implementation can be sped up by storing the midstate after hashing
+# tag_hash instead of rehashing it all the time.
+def tagged_hash(tag: str, msg: bytes) -> bytes:
+    tag_hash = hashlib.sha256(tag.encode()).digest()
+    return hashlib.sha256(tag_hash + tag_hash + msg).digest()
+
+
+def bytes_from_int(x: int) -> bytes:
+    return x.to_bytes(32, byteorder="big")
+
+
+def xor_bytes(b0: bytes, b1: bytes) -> bytes:
+    return bytes(x ^ y for (x, y) in zip(b0, b1))
+
+
+def int_from_bytes(b: bytes) -> int:
+    return int.from_bytes(b, byteorder="big")
+
+
+def hash_sha256(b: bytes) -> bytes:
+    return hashlib.sha256(b).digest()