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Re: [TLS] Enforcing stronger server side signature/hash combinations in TLS 1.2

mrex@sap.com (Martin Rex) Fri, 24 March 2017 15:44 UTC

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From: mrex@sap.com
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Subject: Re: [TLS] Enforcing stronger server side signature/hash combinations in TLS 1.2
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oops, typo:

Martin Rex wrote:
> 
> Actually, looking at the DigiCert issued ECC cert for www.cloudflare.com
> I'm a little confused.
> 
> This is the cert chain (as visualized by Microsoft CryptoAPI):
> 
>   server-cert:  CN=cloudflare.com, ...
>                 contains ECDSA P-256 public key
>                 is allegedly signed with sha256ECDSA
> 
>   intermediate CA:  CN=DigiCert ECC Extended Validation Server CA
>                 contains ECDSA P-384 public key
>                 is allegedly signed with sha384RSA
> 
>   root CA:      CN=DigiCert High Assurance EV Root CA
>                 contains RSA 2048-bit public key
>                 is self-signed with sha1WithRsaEncryption
> 
> For those who insist on reading rfc5246 verbatim, this chain requires
> 
>    ECDSA+SHA384:RSA+SHA384:RSA+SHA1

     ECDSA+SHA256:RSA+SHA384:RSA+SHA1

> 
> The digital signature on the server certificate looks bogus to me,
> that should be a sha384ECDSA signature according to NIST, because
> it uses a P-384 signing key.
> 
> The signature on the intermediate CA is imbalanced, and
> should be sha256RSA rather than sha384RSA. (that is only an interop issue,
> not a security issue).

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