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Customer complained that during security scan performed on our application the following was raised:

172.22.0.19 - xxxxx - IETF X.509 Certificate Signature Collision Vulnerability - https/tcp/172.22.0.19/50000

The keystore (JKS format) has only one self signed certificate.

When I look at the keystore and certificate information I see the following: enter image description here

The signature algorithm is SHA1withRSA (not MD5), so why does the scan raised this problem? Is it related to the certificate fingerprints?

Thanks

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    The fingerprints are local, not in the SSL/TLS protocol at all, and can't be seen by any scanner. That said, I concur with Stephane; worrying about signature collision on selfsigned makes no sense. – dave_thompson_085 Dec 17 '15 at 17:46
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That really depends one what rules where used to trigger the warning and you gave us no information on that.

However, it is possible that your issue is that you have a certificate signed with SHA-1 which is being phased out. That being said, it doesn't make much sense: when using self-signed certificate (or root certificates), the hash is not actually ever used for validating anything.

So, you should go back to the folks who sent your that notification and ask them what they mean: if they start talking about the "certificate signature hash algorythm", you can tell them that it doesn't apply in your case since this is a self-signed cert.

Edit: As requested, here is a reference:

RFC 5280, section 4.1.1.2 (the one defining the X.509v3 standard) defines the "signatureAlgorithm" field like this:

The signatureAlgorithm field contains the identifier for the cryptographic algorithm used by the CA to sign this certificate.

This means that certificates that, in the case of certificates that are NOT signed by a CA (because they are CA certs or simply self-signed), this field has no meaning.

  • Yes, it's most likely that the rule that applied to MD5 was extended also to SHA-1 and you get this error. – Krystian Dec 17 '15 at 13:54
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    Yup. But again, with a self-signed cert or a root CA, it doesn't matter AT ALL: the hash is never used. You could use a CRC without influencing the security – Stephane Dec 17 '15 at 13:56
  • Thanks! Do you know if I can find this documented formally somewhere? – danieln Dec 17 '15 at 14:11
  • @danieln: documented what? If you ask about the error message, you need to ask whoever does the scans. – Krystian Dec 17 '15 at 14:18
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    I Added a reference to the relevant RFC and explanation of why it's relevant – Stephane Dec 17 '15 at 14:19

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