Adopt sslib keygen interface encryption changes

secure-systems-lab/securesystemslib#288 changes the key generation
interface functions in such a way that it is clear if a call opens
a blocking prompt, or writes the key unencrypted. To do this two
functions are added per key type:
 - `generate_and_write_*_keypair_with_prompt`
 - `generate_and_write_unencrypted_*_keypair`

The default `generate_and_write_*_keypair` function now only allows
encrypted keys and only using a passed password. This respects the
principle of secure defaults and least surprise.

sslib#288 furthermore adds a protected
`_generate_and_write_*_keypair`, which is not exposed publicly
because it does not encrypt by default, but is more flexible and
thus convenient e.g. to consume all arguments from a key generation
command line tool such as 'repo.py'.

This commit adds the new public functions to the tuf namespace and
adopts their usage accordingly.

NOTE regarding repo.py:
This commit does not fix any problematic password behavior of
'repo.py' like default passwords, etc. (see #881). It only adopts
the sslib#288 changes to maintain the current behvior, plus
removing one glaringly obsolete password prompt.

NOTE regarding key import:
The securesystemslib private key import functions were also changed
to no longer auto-prompt for decryption passwords , TUF, however,
only exposes custom wrappers (see repository_lib) that do
auto-prompt. sslib#288 changes to the prompt texts are nevertheless
propagated to tuf and reflected in this commit.

Signed-off-by: Lukas Puehringer <lukas.puehringer@nyu.edu>

Author: Lukas Puehringer

docs/TUTORIAL.md

@@ -96,14 +96,15 @@ text without prepended symbols is the output of a command.
 # following function creates an RSA key pair, where the private key is saved to
 # "root_key" and the public key to "root_key.pub" (both saved to the current
 # working directory).
->>> generate_and_write_rsa_keypair("root_key", bits=2048, password="password")
+>>> generate_and_write_rsa_keypair(password="password", filepath="root_key", bits=2048)
 
 # If the key length is unspecified, it defaults to 3072 bits. A length of less
-# than 2048 bits raises an exception. A password may be supplied as an
-# argument, otherwise a user prompt is presented.  If an empty password
-# is entered, the private key is saved unencrypted.
->>> generate_and_write_rsa_keypair("root_key2")
-Enter a password for the RSA key (/path/to/root_key2):
+# than 2048 bits raises an exception. A similar function is available to supply
+# a password on the prompt. If an empty password is entered, the private key
+# is saved unencrypted.
+>>> generate_and_write_rsa_keypair_with_prompt(filepath="root_key2")
+enter password to encrypt private key file '/path/to/root_key2'
+(leave empty if key should not be encrypted):
 Confirm:
 ```
 The following four key files should now exist:
@@ -117,8 +118,9 @@ If a filepath is not given, the KEYID of the generated key is used as the
 filename.  The key files are written to the current working directory.
 ```python
 # Continuing from the previous section . . .
->>> generate_and_write_rsa_keypair()
-Enter a password for the encrypted RSA key (/path/to/b5b8de8aeda674bce948fbe82cab07e309d6775fc0ec299199d16746dc2bd54c):
+>>> generate_and_write_rsa_keypair_with_prompt()
+enter password to encrypt private key file '/path/to/KEYID'
+(leave empty if key should not be encrypted):
 Confirm:
 ```
 
@@ -132,36 +134,27 @@ Confirm:
 # Import an existing private key.  Importing a private key requires a password,
 # whereas importing a public key does not.
 >>> private_root_key = import_rsa_privatekey_from_file("root_key")
-Enter a password for the encrypted RSA key (/path/to/root_key):
-```
-
-`import_rsa_privatekey_from_file()` raises a
-`securesystemslib.exceptions.CryptoError` exception if the key / password is
-invalid:
-
-```
-securesystemslib.exceptions.CryptoError: RSA (public, private) tuple cannot be
-generated from the encrypted PEM string: Bad decrypt. Incorrect password?
+enter password to decrypt private key file '/path/to/root_key'
+(leave empty if key not encrypted):
 ```
 
 ### Create and Import Ed25519 Keys ###
 ```Python
 # Continuing from the previous section . . .
 
-# Generate and write an Ed25519 key pair.  A 'password' argument may be
-# supplied, otherwise a prompt is presented.  The private key is saved
-# encrypted if a non-empty password is given, and unencrypted if the password
-# is empty.
->>> generate_and_write_ed25519_keypair('ed25519_key')
-Enter a password for the Ed25519 key (/path/to/ed25519_key):
+# The same generation and import functions as for rsa keys exist for ed25519
+>>> generate_and_write_ed25519_keypair_with_prompt(filepath='ed25519_key')
+enter password to encrypt private key file '/path/to/ed25519_key'
+(leave empty if key should not be encrypted):
 Confirm:
 
 # Import the ed25519 public key just created . . .
 >>> public_ed25519_key = import_ed25519_publickey_from_file('ed25519_key.pub')
 
 # and its corresponding private key.
 >>> private_ed25519_key = import_ed25519_privatekey_from_file('ed25519_key')
-Enter a password for the encrypted Ed25519 key (/path/to/ed25519_key):
+enter password to decrypt private key file '/path/to/ed25519_key'
+(leave empty if key should not be encrypted):
 ```
 
 Note: Methods are also available to generate and write keys from memory.
@@ -259,26 +252,20 @@ secure manner.
 >>> import datetime
 
 # Generate keys for the remaining top-level roles.  The root keys have been set above.
-# The password argument may be omitted if a password prompt is needed.
->>> generate_and_write_rsa_keypair('targets_key', password='password')
->>> generate_and_write_rsa_keypair('snapshot_key', password='password')
->>> generate_and_write_rsa_keypair('timestamp_key', password='password')
+>>> generate_and_write_rsa_keypair(password='password', filepath='targets_key')
+>>> generate_and_write_rsa_keypair(password='password', filepath='snapshot_key')
+>>> generate_and_write_rsa_keypair(password='password', filepath='timestamp_key')
 
 # Add the verification keys of the remaining top-level roles.
 
 >>> repository.targets.add_verification_key(import_rsa_publickey_from_file('targets_key.pub'))
 >>> repository.snapshot.add_verification_key(import_rsa_publickey_from_file('snapshot_key.pub'))
 >>> repository.timestamp.add_verification_key(import_rsa_publickey_from_file('timestamp_key.pub'))
 
-# Import the signing keys of the remaining top-level roles.  Prompt for passwords.
->>> private_targets_key = import_rsa_privatekey_from_file('targets_key')
-Enter a password for the encrypted RSA key (/path/to/targets_key):
-
->>> private_snapshot_key = import_rsa_privatekey_from_file('snapshot_key')
-Enter a password for the encrypted RSA key (/path/to/snapshot_key):
-
->>> private_timestamp_key = import_rsa_privatekey_from_file('timestamp_key')
-Enter a password for the encrypted RSA key (/path/to/timestamp_key):
+# Import the signing keys of the remaining top-level roles.
+>>> private_targets_key = import_rsa_privatekey_from_file('targets_key', password='password')
+>>> private_snapshot_key = import_rsa_privatekey_from_file('snapshot_key', password='password')
+>>> private_timestamp_key = import_rsa_privatekey_from_file('timestamp_key', password='password')
 
 # Load the signing keys of the remaining roles so that valid signatures are
 # generated when repository.writeall() is called.
@@ -390,18 +377,21 @@ metadata.  `snapshot.json` keys must be loaded and its metadata signed because
 # The private key of the updated targets metadata must be re-loaded before it
 # can be signed and written (Note the load_repository() call above).
 >>> private_targets_key = import_rsa_privatekey_from_file('targets_key')
-Enter a password for the encrypted RSA key (/path/to/targets_key):
+enter password to decrypt private key file '/path/to/targets_key'
+(leave empty if key not encrypted):
 
 >>> repository.targets.load_signing_key(private_targets_key)
 
 # Due to the load_repository() and new versions of metadata, we must also load
 # the private keys of Snapshot and Timestamp to generate a valid set of metadata.
 >>> private_snapshot_key = import_rsa_privatekey_from_file('snapshot_key')
-Enter a password for the encrypted RSA key (/path/to/snapshot_key):
+enter password to decrypt private key file '/path/to/snapshot_key'
+(leave empty if key not encrypted):
 >>> repository.snapshot.load_signing_key(private_snapshot_key)
 
 >>> private_timestamp_key = import_rsa_privatekey_from_file('timestamp_key')
-Enter a password for the encrypted RSA key (/path/to/timestamp_key):
+enter password to decrypt private key file '/path/to/timestamp_key'
+(leave empty if key not encrypted):
 >>> repository.timestamp.load_signing_key(private_timestamp_key)
 
 # Mark roles for metadata update (see #964, #958)
@@ -451,7 +441,7 @@ threshold, it needs to be added to `root.json`, e.g. via
 >>> from securesystemslib.formats import encode_canonical
 >>> from securesystemslib.keys import create_signature
 >>> private_ed25519_key = import_ed25519_privatekey_from_file('ed25519_key')
-Enter a password for the encrypted Ed25519 key (/path/to/ed25519_key):
+enter password to decrypt private key file '/path/to/ed25519_key'
 >>> signature = create_signature(
 ...     private_ed25519_key, encode_canonical(signable_content).encode())
 ```
@@ -489,7 +479,7 @@ targets and generate signed metadata.
 # Continuing from the previous section . . .
 
 # Generate a key for a new delegated role named "unclaimed".
->>> generate_and_write_rsa_keypair('unclaimed_key', bits=2048, password='password')
+>>> generate_and_write_rsa_keypair(password='password', filepath='unclaimed_key', bits=2048)
 >>> public_unclaimed_key = import_rsa_publickey_from_file('unclaimed_key.pub')
 
 # Make a delegation (delegate trust of 'myproject/*.txt' files) from "targets"
@@ -502,8 +492,7 @@ targets and generate signed metadata.
 
 # Load the private key of "unclaimed" so that unclaimed's metadata can be
 # signed, and valid metadata created.
->>> private_unclaimed_key = import_rsa_privatekey_from_file('unclaimed_key')
-Enter a password for the encrypted RSA key (/path/to/unclaimed_key):
+>>> private_unclaimed_key = import_rsa_privatekey_from_file('unclaimed_key', password='password')
 
 >>> repository.targets("unclaimed").load_signing_key(private_unclaimed_key)
 

tests/repository_data/generate.py

@@ -59,11 +59,11 @@
   # Generate public and private key files for the top-level roles, and two
   # delegated roles (these number of keys should be sufficient for most of the
   # unit tests).  Unit tests may generate additional keys, if needed.
-  generate_and_write_rsa_keypair(root_key_file, password='password')
-  generate_and_write_ed25519_keypair(targets_key_file, password='password')
-  generate_and_write_ed25519_keypair(snapshot_key_file, password='password')
-  generate_and_write_ed25519_keypair(timestamp_key_file, password='password')
-  generate_and_write_ed25519_keypair(delegation_key_file, password='password')
+  generate_and_write_rsa_keypair(password='password', filepath=root_key_file)
+  generate_and_write_ed25519_keypair(password='password', filepath=targets_key_file)
+  generate_and_write_ed25519_keypair(password='password', filepath=snapshot_key_file)
+  generate_and_write_ed25519_keypair(password='password', filepath=timestamp_key_file)
+  generate_and_write_ed25519_keypair(password='password', filepath=delegation_key_file)
 
 # Import the public keys.  These keys are needed so that metadata roles are
 # assigned verification keys, which clients use to verify the signatures created

tests/test_repository_lib.py

@@ -143,7 +143,7 @@ def test_import_ed25519_privatekey_from_file(self):
     temporary_directory = tempfile.mkdtemp(dir=self.temporary_directory)
     ed25519_keypath = os.path.join(temporary_directory, 'ed25519_key')
     securesystemslib.interface.generate_and_write_ed25519_keypair(
-        ed25519_keypath, password='pw')
+        password='pw', filepath=ed25519_keypath)
 
     imported_ed25519_key = \
       repo_lib.import_ed25519_privatekey_from_file(ed25519_keypath, 'pw')

tests/test_tutorial.py

@@ -75,11 +75,11 @@ def test_tutorial(self):
 
     # ----- Tutorial Section:  Keys
 
-    generate_and_write_rsa_keypair('root_key', bits=2048, password='password')
+    generate_and_write_rsa_keypair(password='password', filepath='root_key', bits=2048)
 
     # Skipping user entry of password
-    ## generate_and_write_rsa_keypair('root_key2')
-    generate_and_write_rsa_keypair('root_key2', password='password')
+    ## generate_and_write_rsa_keypair_with_prompt('root_key2')
+    generate_and_write_rsa_keypair(password='password', filepath='root_key2')
 
     # Tutorial tells users to expect these files to exist:
     # ['root_key', 'root_key.pub', 'root_key2', 'root_key2.pub']
@@ -109,8 +109,8 @@ def test_tutorial(self):
     # ----- Tutorial Section: Create and Import Ed25519 Keys
 
     # Skipping user entry of password
-    ## generate_and_write_ed25519_keypair('ed25519_key')
-    generate_and_write_ed25519_keypair('ed25519_key', password='password')
+    ## generate_and_write_ed25519_keypair_with_prompt('ed25519_key')
+    generate_and_write_ed25519_keypair(password='password', filepath='ed25519_key')
 
     public_ed25519_key = import_ed25519_publickey_from_file('ed25519_key.pub')
 
@@ -157,9 +157,9 @@ def test_tutorial(self):
         repr('targets') + " role contains 0 / 1 signatures."
       ], [args[0] for args, _ in mock_logger.info.call_args_list])
 
-    generate_and_write_rsa_keypair('targets_key', password='password')
-    generate_and_write_rsa_keypair('snapshot_key', password='password')
-    generate_and_write_rsa_keypair('timestamp_key', password='password')
+    generate_and_write_rsa_keypair(password='password', filepath='targets_key')
+    generate_and_write_rsa_keypair(password='password', filepath='snapshot_key')
+    generate_and_write_rsa_keypair(password='password', filepath='timestamp_key')
 
     repository.targets.add_verification_key(import_rsa_publickey_from_file(
         'targets_key.pub'))
@@ -309,7 +309,7 @@ def test_tutorial(self):
 
     # ----- Tutorial Section: Delegations
     generate_and_write_rsa_keypair(
-        'unclaimed_key', bits=2048, password='password')
+        password='password', filepath='unclaimed_key', bits=2048)
     public_unclaimed_key = import_rsa_publickey_from_file('unclaimed_key.pub')
     repository.targets.delegate(
         'unclaimed', [public_unclaimed_key], ['myproject/*.txt'])

tuf/README-developer-tools.md

@@ -53,15 +53,16 @@ is the private key.
 
 ```
 >>> from tuf.developer_tool import *
->>> generate_and_write_rsa_keypair("path/to/key")
-Enter a password for the RSA key:
+>>> generate_and_write_rsa_keypair_with_prompt(filepath="path/to/key")
+enter password to encrypt private key file 'path/to/key'
+(leave empty if key should not be encrypted):
 Confirm:
 >>>
 ```
 
 We can also use the bits parameter to set a different key length (the default
-is 3072). We can also provide the password parameter in order to suppress the
-password prompt.
+is 3072). We can also `generate_and_write_rsa_keypair` with a `password`
+parameter if a prompt is not desired.
 
 In this example we will be using rsa keys, but ed25519 keys are also supported.
 
@@ -257,7 +258,7 @@ When generating keys, it is possible to specify the length of the key in bits
 and its password as parameters:
 
 ```
->>> generate_and_write_rsa_keypair("path/to/key", bits=2048, password="pw")
+>>> generate_and_write_rsa_keypair(password="pw", filepath="path/to/key", bits=2048)
 ```
 The bits parameter defaults to 3072, and values below 2048 will raise an error.
 The password parameter is only intended to be used in scripts.

tuf/developer_tool.py

@@ -76,7 +76,14 @@
 
 from securesystemslib.interface import (
     generate_and_write_rsa_keypair,
+    generate_and_write_rsa_keypair_with_prompt,
+    generate_and_write_unencrypted_rsa_keypair,
+    generate_and_write_ecdsa_keypair,
+    generate_and_write_ecdsa_keypair_with_prompt,
+    generate_and_write_unencrypted_ecdsa_keypair,
     generate_and_write_ed25519_keypair,
+    generate_and_write_ed25519_keypair_with_prompt,
+    generate_and_write_unencrypted_ed25519_keypair,
     import_rsa_publickey_from_file,
     import_ed25519_publickey_from_file,
     import_ed25519_privatekey_from_file)

tuf/repository_tool.py

@@ -74,8 +74,14 @@
 
 from securesystemslib.interface import (
     generate_and_write_rsa_keypair,
+    generate_and_write_rsa_keypair_with_prompt,
+    generate_and_write_unencrypted_rsa_keypair,
     generate_and_write_ecdsa_keypair,
+    generate_and_write_ecdsa_keypair_with_prompt,
+    generate_and_write_unencrypted_ecdsa_keypair,
     generate_and_write_ed25519_keypair,
+    generate_and_write_ed25519_keypair_with_prompt,
+    generate_and_write_unencrypted_ed25519_keypair,
     import_rsa_publickey_from_file,
     import_ecdsa_publickey_from_file,
     import_ed25519_publickey_from_file,

tuf/scripts/repo.py

@@ -189,6 +189,8 @@
 # securesystemslib.
 SUPPORTED_KEY_TYPES = ('ed25519', 'ecdsa-sha2-nistp256', 'rsa')
 
+# pylint: disable=protected-access
+# ... to allow use of sslib _generate_and_write_*_keypair convenience methods
 
 def process_command_line_arguments(parsed_arguments):
   """
@@ -379,23 +381,30 @@ def gen_key(parsed_arguments):
 
   keypath = None
 
+  keygen_kwargs = {
+      "password": parsed_arguments.pw,
+      "filepath": parsed_arguments.filename,
+      "prompt": (not parsed_arguments.pw) # prompt if no default or passed pw
+  }
+
   if parsed_arguments.key not in SUPPORTED_CLI_KEYTYPES:
     tuf.exceptions.Error(
         'Invalid key type: ' + repr(parsed_arguments.key) + '.  Supported'
         ' key types: ' + repr(SUPPORTED_CLI_KEYTYPES))
 
   elif parsed_arguments.key == ECDSA_KEYTYPE:
-    keypath = securesystemslib.interface.generate_and_write_ecdsa_keypair(
-      parsed_arguments.filename, password=parsed_arguments.pw)
+    keypath = securesystemslib.interface._generate_and_write_ecdsa_keypair(
+        **keygen_kwargs)
 
   elif parsed_arguments.key == ED25519_KEYTYPE:
-    keypath = securesystemslib.interface.generate_and_write_ed25519_keypair(
-        parsed_arguments.filename, password=parsed_arguments.pw)
+    keypath = securesystemslib.interface._generate_and_write_ed25519_keypair(
+        **keygen_kwargs)
 
   # RSA key..
   else:
-    keypath = securesystemslib.interface.generate_and_write_rsa_keypair(
-        parsed_arguments.filename, password=parsed_arguments.pw)
+    keypath = securesystemslib.interface._generate_and_write_rsa_keypair(
+        **keygen_kwargs)
+
 
   # If a filename is not given, the generated keypair is saved to the current
   # working directory.  By default, the keypair is written to <KEYID>.pub
@@ -889,26 +898,27 @@ def set_top_level_keys(repository, parsed_arguments):
   Generate, write, and set the top-level keys.  'repository' is modified.
   """
 
-  # Examples of how the --pw command-line option is interpreted:
-  # repo.py --init': parsed_arguments.pw = 'pw'
-  # repo.py --init --pw my_pw: parsed_arguments.pw = 'my_pw'
-  # repo.py --init --pw: The user is prompted for a password, here.
-  if not parsed_arguments.pw:
-    parsed_arguments.pw = securesystemslib.interface.get_password(
-        prompt='Enter a password for the top-level role keys: ', confirm=True)
-
-  repo_tool.generate_and_write_ed25519_keypair(
-      os.path.join(parsed_arguments.path, KEYSTORE_DIR,
-      ROOT_KEY_NAME), password=parsed_arguments.root_pw)
-  repo_tool.generate_and_write_ed25519_keypair(
-      os.path.join(parsed_arguments.path, KEYSTORE_DIR,
-      TARGETS_KEY_NAME), password=parsed_arguments.targets_pw)
-  repo_tool.generate_and_write_ed25519_keypair(
-      os.path.join(parsed_arguments.path, KEYSTORE_DIR,
-      SNAPSHOT_KEY_NAME), password=parsed_arguments.snapshot_pw)
-  repo_tool.generate_and_write_ed25519_keypair(
-      os.path.join(parsed_arguments.path, KEYSTORE_DIR,
-      TIMESTAMP_KEY_NAME), password=parsed_arguments.timestamp_pw)
+  # Examples of how the --*_pw command-line options are interpreted:
+  # repo.py --init': parsed_arguments.*_pw = 'pw'
+  # repo.py --init --*_pw my_pw: parsed_arguments.*_pw = 'my_pw'
+  # repo.py --init --*_pw: The user is prompted for a password.
+
+  securesystemslib.interface._generate_and_write_ed25519_keypair(
+      password=parsed_arguments.root_pw,
+      filepath=os.path.join(parsed_arguments.path, KEYSTORE_DIR, ROOT_KEY_NAME),
+      prompt=(not parsed_arguments.root_pw))
+  securesystemslib.interface._generate_and_write_ed25519_keypair(
+      password=parsed_arguments.targets_pw,
+      filepath=os.path.join(parsed_arguments.path, KEYSTORE_DIR, TARGETS_KEY_NAME),
+      prompt=(not parsed_arguments.targets_pw))
+  securesystemslib.interface._generate_and_write_ed25519_keypair(
+      password=parsed_arguments.snapshot_pw,
+      filepath=os.path.join(parsed_arguments.path, KEYSTORE_DIR, SNAPSHOT_KEY_NAME),
+      prompt=(not parsed_arguments.snapshot_pw))
+  securesystemslib.interface._generate_and_write_ed25519_keypair(
+      password=parsed_arguments.timestamp_pw,
+      filepath=os.path.join(parsed_arguments.path, KEYSTORE_DIR, TIMESTAMP_KEY_NAME),
+      prompt=(not parsed_arguments.timestamp_pw))
 
   # Import the private keys.  They are needed to generate the signatures
   # included in metadata.