Replace the only EGD call by urandom

Also harmonize documentation.  #boyScout

1 files changed, 67 insertions, 30 deletions

diff --git a/src/OpenSSL/rand.py b/src/OpenSSL/rand.py
index 65cd597..c12638f 100644
--- a/src/OpenSSL/rand.py
+++ b/src/OpenSSL/rand.py
@@ -1,9 +1,10 @@
 """
 PRNG management routines, thin wrappers.
-
-See the file RATIONALE for a short explanation of why this module was written.
 """
 
+import os
+import warnings
+
 from functools import partial
 
 from six import integer_types as _integer_types
@@ -17,7 +18,17 @@ from OpenSSL._util import (
 
 class Error(Exception):
     """
-    An error occurred in an `OpenSSL.rand` API.
+    An error occurred in an :mod:`OpenSSL.rand` API.
+
+    If the current RAND method supports any errors, this is raised when needed.
+    The default method does not raise this when the entropy pool is depleted.
+
+    Whenever this exception is raised directly, it has a list of error messages
+    from the OpenSSL error queue, where each item is a tuple *(lib, function,
+    reason)*. Here *lib*, *function* and *reason* are all strings, describing
+    where and what the problem is.
+
+    See :manpage:`err(3)` for more information.
     """
 
 _raise_current_error = partial(_exception_from_error_queue, Error)
@@ -29,10 +40,13 @@ _builtin_bytes = bytes
 
 def bytes(num_bytes):
     """
-    Get some random bytes as a string.
+    Get some random bytes from the PRNG as a string.
+
+    This is a wrapper for the C function ``RAND_bytes``.
 
-    :param num_bytes: The number of bytes to fetch
-    :return: A string of random bytes
+    :param num_bytes: The number of bytes to fetch.
+
+    :return: A string of random bytes.
     """
     if not isinstance(num_bytes, _integer_types):
         raise TypeError("num_bytes must be an integer")
@@ -52,11 +66,17 @@ def bytes(num_bytes):
 
 def add(buffer, entropy):
     """
-    Add data with a given entropy to the PRNG
+    Mix bytes from *string* into the PRNG state.
 
-    :param buffer: Buffer with random data
-    :param entropy: The entropy (in bytes) measurement of the buffer
-    :return: None
+    The *entropy* argument is (the lower bound of) an estimate of how much
+    randomness is contained in *string*, measured in bytes.
+
+    For more information, see e.g. :rfc:`1750`.
+
+    :param buffer: Buffer with random data.
+    :param entropy: The entropy (in bytes) measurement of the buffer.
+
+    :return: :obj:`None`
     """
     if not isinstance(buffer, _builtin_bytes):
         raise TypeError("buffer must be a byte string")
@@ -70,10 +90,11 @@ def add(buffer, entropy):
 
 def seed(buffer):
     """
-    Alias for rand_add, with entropy equal to length
+    Equivalent to calling :func:`add` with *entropy* as the length of *buffer*.
 
     :param buffer: Buffer with random data
-    :return: None
+
+    :return: :obj:`None`
     """
     if not isinstance(buffer, _builtin_bytes):
         raise TypeError("buffer must be a byte string")
@@ -84,24 +105,33 @@ def seed(buffer):
 
 def status():
     """
-    Retrieve the status of the PRNG
+    Check whether the PRNG has been seeded with enough data.
 
-    :return: True if the PRNG is seeded enough, false otherwise
+    :return: :obj:`True` if the PRNG is seeded enough, :obj:`False` otherwise.
     """
     return _lib.RAND_status()
 
 
 def egd(path, bytes=_unspecified):
     """
-    Query an entropy gathering daemon (EGD) for random data and add it to the
-    PRNG. I haven't found any problems when the socket is missing, the function
-    just returns 0.
+    Query the system random source and seed the PRNG.
+
+    Does *not* actually query the EGD.
+
+    .. deprecated:: 15.2.0
+        EGD was only necessary for some commercial UNIX systems that all
+        reached their ends of life more than a decade ago.  See
+        `pyca/cryptography#1636
+        <https://github.com/pyca/cryptography/pull/1636>`_.
+
+    :param path: Ignored.
+    :param bytes: (optional) The number of bytes to read, default is 255.
 
-    :param path: The path to the EGD socket
-    :param bytes: (optional) The number of bytes to read, default is 255
-    :returns: The number of bytes read (NB: a value of 0 isn't necessarily an
-              error, check rand.status())
+    :returns: ``len(bytes)`` or 255 if not specified.
     """
+    warnings.warn("OpenSSL.rand.egd() is deprecated as of 15.2.0.",
+                  DeprecationWarning)
+
     if not isinstance(path, _builtin_bytes):
         raise TypeError("path must be a byte string")
 
@@ -110,14 +140,17 @@ def egd(path, bytes=_unspecified):
     elif not isinstance(bytes, int):
         raise TypeError("bytes must be an integer")
 
-    return _lib.RAND_egd_bytes(path, bytes)
+    seed(os.urandom(bytes))
+    return bytes
 
 
 def cleanup():
     """
     Erase the memory used by the PRNG.
 
-    :return: None
+    This is a wrapper for the C function ``RAND_cleanup``.
+
+    :return: :obj:`None`
     """
     # TODO Nothing tests this call actually being made, or made properly.
     _lib.RAND_cleanup()
@@ -125,11 +158,13 @@ def cleanup():
 
 def load_file(filename, maxbytes=_unspecified):
     """
-    Seed the PRNG with data from a file
+    Read *maxbytes* of data from *filename* and seed the PRNG with it.
+
+    Read the whole file if *maxbytes* is not specified or negative.
 
     :param filename: The file to read data from (``bytes`` or ``unicode``).
-    :param maxbytes: (optional) The number of bytes to read, default is to read
-        the entire file
+    :param maxbytes: (optional) The number of bytes to read.    Default is to
+        read the entire file.
 
     :return: The number of bytes read
     """
@@ -145,11 +180,12 @@ def load_file(filename, maxbytes=_unspecified):
 
 def write_file(filename):
     """
-    Save PRNG state to a file
+    Write a number of random bytes (currently 1024) to the file *path*.  This
+    file can then be used with :func:`load_file` to seed the PRNG again.
 
     :param filename: The file to write data to (``bytes`` or ``unicode``).
 
-    :return: The number of bytes written
+    :return: The number of bytes written.
     """
     filename = _path_string(filename)
     return _lib.RAND_write_file(filename)
@@ -158,8 +194,9 @@ def write_file(filename):
 # TODO There are no tests for screen at all
 def screen():
     """
-    Add the current contents of the screen to the PRNG state. Availability:
-    Windows.
+    Add the current contents of the screen to the PRNG state.
+
+    Availability: Windows.
 
     :return: None
     """