[New-bugs-announce] [issue40645] Use OpenSSL's HMAC API

[Christian Heimes]

New submission from Christian Heimes <lists at cheimes.de>:

Python's hmac module provides a pure Python based implementation on top of the hashlib module. OpenSSL offers a dedicated HMAC implementation that has a couple of benefits over pure Python implementation:

- OpenSSL HMAC is slightly faster and requires slightly less memory and allocations.
- Python's HMAC only works for RFC 2104 HMACs with digests like MD5, SHA1, SHA2, and SHA3. Other digests types like Blake2 use a completely different style of HMAC. OpenSSL's HMAC API works for all sorts of digests. OpenSSL 3.0.0 also supports Blake2 MAC with its standard API.
- OpenSSL HMAC is standard and compliance conform. Certain compliance restrictions require that MAC and keyed hashing is implemented in a certain way. Our HMAC code is considered a custom implementation of a crypto primitive and in violation of compliance rules.

For 3.9 I plan to deprecate hmac.HMAC.digest_con, hmac.HMAC.inner, and hmac.HMAC.outer attributes. They are implementation specific details any way. I'm also going to provide a _hashlib.hmac_new() function so we can test the new code.

For 3.10 I'll be switching over to _haslib.hmac_new() when the digestmod is a string or a callable that returns _hashlib.HASH code.

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assignee: christian.heimes
components: Extension Modules
messages: 369050
nosy: christian.heimes, gregory.p.smith
priority: normal
severity: normal
stage: patch review
status: open
title: Use OpenSSL's HMAC API
type: enhancement
versions: Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue40645>
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