Re: [TLS] Issue 49: Finished.verify length
Eric Rescorla <ekr@networkresonance.com> Fri, 14 September 2007 04:11 UTC
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Date: Thu, 13 Sep 2007 21:07:40 -0700
From: Eric Rescorla <ekr@networkresonance.com>
To: Mike <mike-list@pobox.com>
Subject: Re: [TLS] Issue 49: Finished.verify length
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At Thu, 13 Sep 2007 17:18:39 -0700, Mike wrote: > > > Currently Finished.verify_data is always 12 octets. With newer PRFs > > and hashes, more might be useful. Should this depend on the PRF? > > > > My take on this is that the 12-octet length is mostly independent > > of the PRF. After all, it's already been truncated from either > > MD5 or SHA-1. Is there a good security reason to change this? > > Since the Finished message is just the output of the PRF itself, > you can specify however much output you want. In TLS 1.2, the > default PRF is based on HMAC-SHA-256, so 1 iteration of the PRF > generates 32 bytes. With the Finished message currently using > only 12 bytes of PRF output, we are just throwing away 20 bytes > that could be utilized. Therefore, the Finished message could > be increased to 32 bytes without impacting performance. > > I am not a security expert, but I do know that 32 bytes is a lot > harder to guess than 12. As I recall, the truncation was intended to *increase* security, because it leaked less information about the MS to an active attacker. -Ekr _______________________________________________ TLS mailing list TLS@lists.ietf.org https://www1.ietf.org/mailman/listinfo/tls
- [TLS] Issue 49: Finished.verify length Eric Rescorla
- Re: [TLS] Issue 49: Finished.verify length Mike
- Re: [TLS] Issue 49: Finished.verify length Eric Rescorla
- Re: [TLS] Issue 49: Finished.verify length Mike
- Re: [TLS] Issue 49: Finished.verify length Bodo Moeller
- RE: [TLS] Issue 49: Finished.verify length Pasi.Eronen
- Re: [TLS] Issue 49: Finished.verify length Bodo Moeller
- Re: [TLS] Issue 49: Finished.verify length Bodo Moeller
- RE: [TLS] Issue 49: Finished.verify length Pasi.Eronen
- Re: [TLS] Issue 49: Finished.verify length Eric Rescorla
- Re: [TLS] Issue 49: Finished.verify length Eric Rescorla
- RE: [TLS] Issue 49: Finished.verify length Pasi.Eronen
- Re: [TLS] Issue 49: Finished.verify length Eric Rescorla
- RE: [TLS] Issue 49: Finished.verify length Pasi.Eronen
- Re: [TLS] Issue 49: Finished.verify length Eric Rescorla
- RE: [TLS] Issue 49: Finished.verify length Pasi.Eronen
- Re: [TLS] Issue 49: Finished.verify length Russ Housley