Re: [Unbearable] Possible attack on Token Binding with RSA key exchange
Andrei Popov <Andrei.Popov@microsoft.com> Mon, 04 September 2017 22:59 UTC
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From: Andrei Popov <Andrei.Popov@microsoft.com>
To: Subodh Iyengar <subodh@fb.com>, Nick Harper <nharper@google.com>, IETF Tokbind WG <unbearable@ietf.org>
Thread-Topic: [Unbearable] Possible attack on Token Binding with RSA key exchange
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Date: Mon, 04 Sep 2017 22:59:30 +0000
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Archived-At: <https://mailarchive.ietf.org/arch/msg/unbearable/39HFhLNX_0N2cvmPRK8LO_DaY6U>
Subject: Re: [Unbearable] Possible attack on Token Binding with RSA key exchange
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It seems clear that binding tokens to broken TLS channels does one no good, but I don't mind adding some statements to this effect in the security considerations. The statements would need to be general enough to cover TLS client and server compromise, PFS and non-PFS. Nick, please feel free to author a PR. If we get to IESG review someday, there will be more edits, and we can incorporate this as well. I don't think it makes sense to limit TB to (EC)DHE, especially if we're going to allow TB in combination with TLS 1.3 0-RTT mode. Cheers, Andrei From: Unbearable [mailto:unbearable-bounces@ietf.org] On Behalf Of Subodh Iyengar Sent: Friday, September 1, 2017 3:28 PM To: Nick Harper <nharper@google.com>; IETF Tokbind WG <unbearable@ietf.org> Subject: Re: [Unbearable] Possible attack on Token Binding with RSA key exchange Having said that, even if we only support forward secure ciphers, I do not think we can reasonably claim that we are secure against the threat of stolen private keys. I like the the carrot opportunity this brings to encourage adoption of forward secure cipher suites. Subodh ________________________________ From: Subodh Iyengar Sent: Friday, September 1, 2017 3:24:25 PM To: Nick Harper; IETF Tokbind WG Subject: Re: [Unbearable] Possible attack on Token Binding with RSA key exchange +1 to requiring that token binding only be used with forward secure cipher suites. I believe the extended master secret requirement of token binding prevents the attack on forward secure suites, i.e. an attacker cannot change the DH share advertised by the real server and thus needs to get the private key for it. Subodh ________________________________ From: Unbearable <unbearable-bounces@ietf.org<mailto:unbearable-bounces@ietf.org>> on behalf of Nick Harper <nharper@google.com<mailto:nharper@google.com>> Sent: Friday, September 1, 2017 3:03:37 PM To: IETF Tokbind WG Subject: [Unbearable] Possible attack on Token Binding with RSA key exchange I came across an attack on Token Binding today, which I think is worth addressing in TBPROTO in some fashion (likely another paragraph in Security Considerations). This attack involves an adversary with the private key of a server it wishes to impersonate, and was mentioned in draft-balfanz-tls-channelid in the last paragraph of its Security Considerations. In brief, if an attacker has possession of a server's private key, it can hijack a TLS connection between client and server if the connection uses RSA key exchange instead of (EC)DHE key exchange, which allows the attacker to exercise the bound token without possession of the Token Binding private key. I realize that we're past WGLC at this point, but I think this should be addressed. On one end, we could require forward-secret key exchange modes with Token Binding. We could also describe this specific attack in the Security Considerations, or we could expand the Security Considerations to describe what attacks are and aren't in the Token Binding threat model, to say that attacks where the adversary has the server's private key are out of scope. _______________________________________________ Unbearable mailing list Unbearable@ietf.org<mailto:Unbearable@ietf.org> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.ietf.org_mailman_listinfo_unbearable&d=DwICAg&c=5VD0RTtNlTh3ycd41b3MUw&r=h3Ju9EBS7mHtwg-wAyN7fQ&m=aK_8DMmoWWiiQJmFt3JvhVLT6eh7Qm3nf3WuMhMC7vM&s=B0sKQEO8i8hDpLizsh7X8ins9EGGwOwcckYqZku7zEE&e=<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Furldefense.proofpoint.com%2Fv2%2Furl%3Fu%3Dhttps-3A__www.ietf.org_mailman_listinfo_unbearable%26d%3DDwICAg%26c%3D5VD0RTtNlTh3ycd41b3MUw%26r%3Dh3Ju9EBS7mHtwg-wAyN7fQ%26m%3DaK_8DMmoWWiiQJmFt3JvhVLT6eh7Qm3nf3WuMhMC7vM%26s%3DB0sKQEO8i8hDpLizsh7X8ins9EGGwOwcckYqZku7zEE%26e%3D&data=02%7C01%7CAndrei.Popov%40microsoft.com%7Cd5cf44853d4f4d49fdd008d4f188bfbd%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636399017020307291&sdata=3NraAZRhD041W4k4OzbGj64Y9PCQweJOggRlUa9QswM%3D&reserved=0>
- [Unbearable] Possible attack on Token Binding wit… Nick Harper
- Re: [Unbearable] Possible attack on Token Binding… Subodh Iyengar
- Re: [Unbearable] Possible attack on Token Binding… Subodh Iyengar
- Re: [Unbearable] Possible attack on Token Binding… Andrei Popov
- Re: [Unbearable] Possible attack on Token Binding… Nick Harper
- Re: [Unbearable] Possible attack on Token Binding… Andrei Popov
- Re: [Unbearable] Possible attack on Token Binding… Lanlan Pan