[New-bugs-announce] [issue32433] Provide optimized HMAC digest

[Christian Heimes]

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

hmac.HMAC's flexibility comes with a cost. To create the MAC of a message, it has to create between three and four hash instances (inner, outer, key for long keys, result), multiple bound method objects and other temporary objects. For short messages, memory allocation, object handling and GIL release/acquire operations dominate the performance.

I propose to provide a fast one-shot HMAC function: hmac.digest(key, msg, digstmod) -> bytes function. A PoC implementation based on OpenSSL's HMAC() function and a pure Python implementation as inlined HMAC showed promising performance improvements. The C implementation is 3 times faster.

Standard HMAC:
$ ./python -m timeit -n200000 -s "import hmac" -- "hmac.HMAC(b'key', b'message', 'sha256').digest()"
200000 loops, best of 5: 5.38 usec per loop

Optimized Python code:
$ ./python -m timeit -n 200000 -s "import hmac; hmac._hashopenssl = None" -- "hmac.digest(b'key', b'message', 'sha256')"
200000 loops, best of 5: 3.87 usec per loop

OpenSSL HMAC()
$ ./python -m timeit -n 200000 -s "import hmac" -- "hmac.digest(b'key', b'message', 'sha256')"
200000 loops, best of 5: 1.82 usec per loop

----------
components: Extension Modules
messages: 309097
nosy: christian.heimes, gregory.p.smith
priority: normal
severity: normal
stage: patch review
status: open
title: Provide optimized HMAC digest
type: performance
versions: Python 3.7

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue32433>
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