Re: [TLS] [Technical Errata Reported] RFC7905 (5251)
Adam Langley <agl@google.com> Mon, 12 February 2018 23:30 UTC
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From: Adam Langley <agl@google.com>
Date: Mon, 12 Feb 2018 15:30:11 -0800
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To: RFC Errata System <rfc-editor@rfc-editor.org>
Cc: Wan-Teh Chang <wtc@google.com>, Nikos Mavrogiannopoulos <nmav@redhat.com>, Joachim Strömbergson <joachim@secworks.se>, Simon Josefsson <simon@josefsson.org>, Kathleen Moriarty <Kathleen.Moriarty.ietf@gmail.com>, Eric Rescorla <ekr@rtfm.com>, Joseph Salowey <joe@salowey.net>, sean+ietf@sn3rd.com, xavier.bonnetain@inria.fr, tls@ietf.org
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Subject: Re: [TLS] [Technical Errata Reported] RFC7905 (5251)
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On Thu, Feb 1, 2018 at 5:59 AM, RFC Errata System <rfc-editor@rfc-editor.org > wrote: > Original Text > ------------- > Poly1305 is designed to ensure that forged messages are rejected with > a probability of 1-(n/2^107), where n is the maximum length of the > input to Poly1305. In the case of (D)TLS, this means a maximum > forgery probability of about 1 in 2^93. > > Corrected Text > -------------- > Poly1305 is designed to ensure that forged messages are rejected with > a probability of 1-(n/2^106), where n is the maximum length of the > input to Poly1305. In the case of (D)TLS, this means a maximum > forgery probability of about 1 in 2^92. > I'm not sure that this errata report is correct. The full formula is beyond email HTML to express, but see the "Security Guarantee" section of https://cr.yp.to/mac/poly1305-20050329.pdf The section seems to be talking about blind forgeries, so C = 0. D = 1 because this is a per-attempt measure. Then we have 8*L/16 on the top of the fraction, which is 1/2 * L (where L = byte length of a message). If we multiply top and bottom by two, we get L / 2^107. For (D)TLS, with a maximum encrypted plaintext length of ~2^14, that gives 2^{-93}. Cheers AGL
- [TLS] [Technical Errata Reported] RFC7905 (5251) RFC Errata System
- Re: [TLS] [Technical Errata Reported] RFC7905 (52… Adam Langley
- Re: [TLS] [Technical Errata Reported] RFC7905 (52… Xavier Bonnetain
- Re: [TLS] [Technical Errata Reported] RFC7905 (52… Adam Langley