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Re: Stricter TLS Usage in HTTP/2

From: Eric Rescorla <ekr@rtfm.com>
Date: Thu, 22 May 2014 13:27:58 -0700
Message-ID: <CABcZeBOjvT0LNoKEbtC_eBvuhr9Y0m2gs-GWNKSEEC0yfh0i7g@mail.gmail.com>
To: William Chan (陈智昌) <willchan@chromium.org>
Cc: HTTP Working Group <ietf-http-wg@w3.org>, Adam Langley <agl@google.com>
I have mixed feelings about this.

This is a not-unreasonable cipher suite profile (indeed, it's pretty much
what we
are planning to require in TLS 1.3). I wouldn't be really upset if HTTP
decided to
require this. OTOH, if Chrome has a stricter set of requirements than HTTP,
that seems like it's going to have some pretty negative impacts on user
experience if some servers deploy with only ciphersuites which are not in
Chrome.

-Ekr



On Thu, May 22, 2014 at 12:58 PM, William Chan (陈智昌)
<willchan@chromium.org>wrote:

> I've been coding up https://http2.github.io/http2-spec/#TLSUsage in
> Chromium. When implementing this, I talked to agl@ about what to
> ciphersuites to allow. We ended up deciding to be stricter than the spec.
> For example, we only allow AEADs.
>
> agl@ thought it'd be nice if we could change the spec to reflect
> Chromium's stricter stance here (
> https://codereview.chromium.org/291093002/#msg14). Is this controversial?
> Can we change the spec's guidance here to be more strict?
>
> For exact details, my current patch is at
> https://codereview.chromium.org/291093002/diff/140001/net/ssl/ssl_cipher_suite_names.cc
> :
>
>
>  *348* bool IsSecureTLSCipherSuite(uint16 cipher_suite) { *349*CipherSuite desired = {0};
> *350* desired.cipher_suite = cipher_suite; *351*  *352* void* r =
> bsearch(&desired, *353* kCipherSuites, *354* arraysize(kCipherSuites),
> *355* sizeof(kCipherSuites[0]), *356* CipherSuiteCmp); *357*  *358* if
> (!r) *359* return false; *360*  *361* const CipherSuite* cs =
> static_cast<const CipherSuite*>(r);  *362*  *363* const int key_exchange
> = cs->encoded >> 8; *364* const int cipher = (cs->encoded >> 3) & 0x1f;
> *365* const int mac = cs->encoded & 0x7; *366*  *367* // Only allow
> forward secure key exchanges. *368* switch (key_exchange) { *369* case
> 10: // DHE_RSA *370* case 14: // ECDHE_ECDSA *371* case 16: // ECDHE_RSA
> *372* break; *373* default: *374* return false; *375* } *376*  *377*switch (cipher) {
> *378* case 13: // AES_128_GCM *379* case 14: // AES_256_GCM *380* case
> 17: // CHACHA20_POLY1305 *381* break; *382* default: *383* return false;
> *384* } *385*  *386* // Only AEADs allowed. *387* if (mac !=
> kAEADMACValue) *388* return false; *389*  *390* return true; *391* } *392*
> Cheers.
>
Received on Thursday, 22 May 2014 20:29:06 UTC

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