gh-129327: revise hashlib documentation to account for FIPS removing sha1 (GH-132729)

* gh-129327: revise hashlib documentation to account for FIPS removing sha1

More generally, the current documentation is a bit scattered, talking
about what terms are "equal" despite those terms not being very
interesting and given the term "secure hash", probably wrong (because
md5 and sha1 are not secure anymore).

Let's talk about cryptographically secure instead, and note that two of
them aren't. And then we can also link to the source for NIST going
through the removal process for SHA1.

* Add Gregors Suggestion

* Clean up

---------

Co-authored-by: Eli Schwartz <[email protected]>

Author: StanFromIreland

Doc/library/hashlib.rst

@@ -20,13 +20,11 @@
 
 --------------
 
-This module implements a common interface to many different secure hash and
-message digest algorithms.  Included are the FIPS secure hash algorithms SHA1,
-SHA224, SHA256, SHA384, SHA512, (defined in `the FIPS 180-4 standard`_),
-the SHA-3 series (defined in `the FIPS 202 standard`_) as well as RSA's MD5
-algorithm (defined in internet :rfc:`1321`).  The terms "secure hash" and
-"message digest" are interchangeable.  Older algorithms were called message
-digests.  The modern term is secure hash.
+This module implements a common interface to many different hash algorithms.
+Included are the FIPS secure hash algorithms SHA224, SHA256, SHA384, SHA512,
+(defined in `the FIPS 180-4 standard`_), the SHA-3 series (defined in `the FIPS
+202 standard`_) as well as the legacy algorithms SHA1 (`formerly part of FIPS`_)
+and the MD5 algorithm (defined in internet :rfc:`1321`).
 
 .. note::
 
@@ -812,6 +810,7 @@ Domain Dedication 1.0 Universal:
 .. _the FIPS 180-4 standard: https://csrc.nist.gov/pubs/fips/180-4/upd1/final
 .. _the FIPS 202 standard: https://csrc.nist.gov/pubs/fips/202/final
 .. _HACL\* project: https://github.com/hacl-star/hacl-star
+.. _formerly part of FIPS: https://csrc.nist.gov/news/2023/decision-to-revise-fips-180-4
 
 
 .. _hashlib-seealso: