RE: [EXTERNAL] Openssl 3.5 FIPS and SHA-1

Yes.  See https://csrc.nist.gov/projects/cryptographic-module-validation-program/sp-800-140-series-supplemental-information/sp800-140c .

SHA-1 is still approved for situations where security requires pre-image resistance (given a fixed message M, it is hard to find another message M1 such that Hash(M1) == Hash(M).  An alternative, slightly weaker formulation, is given a fixed value V, it is hard to find a message M1 such that Hash(M1) == V).

The problem with SHA-1 is that it is not collision resistant (it is known how to find two values M1, M2 such that Hash(M1) == Hash(M2)).  Note that the difference with collision resistance, is that the attacker gets to choose both messages.  Collision resistance is the property you want for a hash which is used to digest a message before signing.

Collision resistance implies pre-image resistance, and when building a protocol the safe rule of thumb is to use an algorithm which is collision resistant (SHA-2/SHA-3) just in case collision resistance is the property you need.  However if you have an existing protocol, careful analysis may show it is still currently secure


Martin Bonner


From: [email protected] <[email protected]> On Behalf Of Ken Goldman
Sent: 19 January 2026 23:52
To: [email protected]
Subject: [EXTERNAL] Openssl 3.5 FIPS and SHA-1

Looking at https: //urldefense. com/v3/__https: //docs. openssl. org/3. 5/man7/OSSL_PROVIDER-FIPS/*approved-algorithms__;Iw!!FJ-Y8qCqXTj2!dEDWcfZHH1HIbrmQ8PLFovSXwvQSkAlk3hMHhPo1uGlLk2xfVJPMBlD3_mbHF8p_EDDZd3OZ5IaHJbdq0-Qg$ I see SHA-1 on the list. 


Looking at



https://urldefense.com/v3/__https://docs.openssl.org/3.5/man7/OSSL_PROVIDER-FIPS/*approved-algorithms__;Iw!!FJ-Y8qCqXTj2!dEDWcfZHH1HIbrmQ8PLFovSXwvQSkAlk3hMHhPo1uGlLk2xfVJPMBlD3_mbHF8p_EDDZd3OZ5IaHJbdq0-Qg$<https://urldefense.com/v3/__https:/docs.openssl.org/3.5/man7/OSSL_PROVIDER-FIPS/*approved-algorithms__;Iw!!FJ-Y8qCqXTj2!dEDWcfZHH1HIbrmQ8PLFovSXwvQSkAlk3hMHhPo1uGlLk2xfVJPMBlD3_mbHF8p_EDDZd3OZ5IaHJbdq0-Qg$>



I see SHA-1 on the list. Is SHA-1 really approved?







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