replace predefined ssh keys with generated ones

libs/ssh.py

@@ -0,0 +1,96 @@
+from base64 import b64decode, b64encode
+from functools import lru_cache
+from hashlib import sha3_224
+
+from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey
+from cryptography.hazmat.primitives.serialization import (
+    Encoding,
+    NoEncryption,
+    PrivateFormat,
+    PublicFormat,
+)
+
+from bundlewrap.utils import Fault
+
+
+@lru_cache(maxsize=None)
+def generate_ed25519_private_key(username, node):
+    return Fault(
+        f'private key {username}@{node.name}',
+        lambda username, node: _generate_ed25519_private_key(username, node),
+        username=username,
+        node=node,
+    )
+
+
+@lru_cache(maxsize=None)
+def generate_ed25519_public_key(username, node):
+    return Fault(
+        f'public key {username}@{node.name}',
+        lambda username, node: _generate_ed25519_public_key(username, node),
+        username=username,
+        node=node,
+    )
+
+
+def _generate_ed25519_private_key(username, node):
+    privkey_bytes = Ed25519PrivateKey.from_private_bytes(_secret(username, node))
+
+    nondeterministic_privatekey = privkey_bytes.private_bytes(
+        encoding=Encoding.PEM,
+        format=PrivateFormat.OpenSSH,
+        encryption_algorithm=NoEncryption(),
+    ).decode()
+
+    # get relevant lines from string
+    nondeterministic_bytes = b64decode(
+        ''.join(nondeterministic_privatekey.split('\n')[1:-2])
+    )
+
+    # sanity check
+    if nondeterministic_bytes[98:102] != nondeterministic_bytes[102:106]:
+        raise Exception("checksums should be the same: whats going on here?")
+
+    # replace random bytes with deterministic values
+    random_bytes = sha3_224(_secret(username, node)).digest()[0:4]
+    deterministic_bytes = (
+        nondeterministic_bytes[:98]
+        + random_bytes
+        + random_bytes
+        + nondeterministic_bytes[106:]
+    )
+
+    # reassemble file
+    deterministic_privatekey = '\n'.join(
+        [
+            '-----BEGIN OPENSSH PRIVATE KEY-----',
+            b64encode(deterministic_bytes).decode(),
+            '-----END OPENSSH PRIVATE KEY-----',
+        ]
+    ) + '\n'
+
+    return deterministic_privatekey
+
+
+def _generate_ed25519_public_key(username, node):
+    return (
+        Ed25519PrivateKey.from_private_bytes(_secret(username, node))
+        .public_key()
+        .public_bytes(
+            encoding=Encoding.OpenSSH,
+            format=PublicFormat.OpenSSH,
+        )
+        .decode()
+        + f' {username}@{node.name}'
+    )
+
+
+@lru_cache(maxsize=None)
+def _secret(username, node):
+    return b64decode(
+        str(
+            node.repo.vault.random_bytes_as_base64_for(
+                f"{username}@{node.name}", length=32
+            )
+        )
+    )