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[3.14] gh-135244: generate UUID random Node ID with a CSPRNG as per RFC 9562, §6.10.3 (GH-135226) #135255

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Jun 8, 2025
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[3.14] gh-135244: generate UUID random Node ID with a CSPRNG as per RFC 9562, §6.10.3 (GH-135226) #135255

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4 changes: 4 additions & 0 deletions Doc/library/uuid.rst
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Expand Up @@ -257,6 +257,10 @@ The :mod:`uuid` module defines the following functions:
non-specified arguments are substituted for a pseudo-random integer of
appropriate size.

By default, *a*, *b* and *c* are generated by a non-cryptographically
secure pseudo-random number generator (CSPRNG). Use :func:`uuid4` when
a UUID needs to be used in a security-sensitive context.

.. versionadded:: 3.14


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14 changes: 8 additions & 6 deletions Lib/uuid.py
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Expand Up @@ -656,18 +656,20 @@ def _windll_getnode():

def _random_getnode():
"""Get a random node ID."""
# RFC 4122, $4.1.6 says "For systems with no IEEE address, a randomly or
# pseudo-randomly generated value may be used; see Section 4.5. The
# multicast bit must be set in such addresses, in order that they will
# never conflict with addresses obtained from network cards."
# RFC 9562, §6.10-3 says that
#
# Implementations MAY elect to obtain a 48-bit cryptographic-quality
# random number as per Section 6.9 to use as the Node ID. [...] [and]
# implementations MUST set the least significant bit of the first octet
# of the Node ID to 1. This bit is the unicast or multicast bit, which
# will never be set in IEEE 802 addresses obtained from network cards.
#
# The "multicast bit" of a MAC address is defined to be "the least
# significant bit of the first octet". This works out to be the 41st bit
# counting from 1 being the least significant bit, or 1<<40.
#
# See https://en.wikipedia.org/w/index.php?title=MAC_address&oldid=1128764812#Universal_vs._local_(U/L_bit)
import random
return random.getrandbits(48) | (1 << 40)
return int.from_bytes(os.urandom(6)) | (1 << 40)


# _OS_GETTERS, when known, are targeted for a specific OS or platform.
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4 changes: 4 additions & 0 deletions Misc/NEWS.d/next/Library/2025-06-08-10-22-22.gh-issue-135244.Y2SOTJ.rst
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@@ -0,0 +1,4 @@
:mod:`uuid`: when the MAC address cannot be determined, the 48-bit node
ID is now generated with a cryptographically-secure pseudo-random number
generator (CSPRNG) as per :rfc:`RFC 9562, §6.10.3 <9562#section-6.10-3>`.
This affects :func:`~uuid.uuid1` and :func:`~uuid.uuid6`.
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