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I was wondering whether SHA-1 deprecation would create any security concern for self signed (internally used) already existing certificates. What is the right thing to do in this case? Since the discovered vulnerability does not allow an attacker to create another document with the same hash as an already existing document organizations using already existing certificated should not be effected, right?

Should the SHA-1 hash algorithm still be allowed for this scenario?

marked as duplicate by Anders, Gilles, Serge Ballesta, Steve, CaffeineAddiction Mar 21 '17 at 16:39

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  • For which purpose are those internal certs used ? I wonder what information you didn't found in the related question list on the right... – Tensibai Mar 21 '17 at 10:14
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Self signed certificates are not affected.

With the ability to create a hash collision an attacker can create two certificate requests, one for legit.com and one for evilattacker.com, with the same hash. The certificate authority will then sign legit.com and the attacker can use the signature to create a valid certificate for evilattacker.com, and vice versa.

With self signed certificates, you control both the request and the signing, so this scenario does not apply. As long as you don't sign certificate signing requests that were created by people you don't trust, you are safe.

It is still a good idea to use newer hash functions for all your future certificates.

Edit: note that you are also dependent on browser behavior if you want to keep using SHA1 certificates.

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