Re: [Mathmesh] UDF Design notes
Michael Richardson <mcr+ietf@sandelman.ca> Wed, 14 August 2019 23:45 UTC
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Date: Wed, 14 Aug 2019 19:45:13 -0400
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Subject: Re: [Mathmesh] UDF Design notes
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Phillip Hallam-Baker <phill@hallambaker.com> wrote: > The original starting point was the need for a 'better PGP fingerprint'. In > particular, I wanted a digest representation that was: > * Reasonably compact in both printed and voiced form. > * Supported use of SHA2 > * Could be expressed at varying precision as the application needs demanded > * Could be upgraded to make use of new algorithms if absolutely necessary > * Could be input via a keyboard > * Could be compared for equality > * Could be used to create a fingerprint of any type of data (not just keys) > * Support use in QR codes, DNS labels, etc. I think that this was a rather ambitious set of requirements :-) > The choice of Base32 comes from the observation that fingerprints are > frequently read out aloud and having to distinguish case makes the process > tedious and error prone. So it cant be Base64 but Base32 gives us five bits > per char instead of four. I agree with your use. I wonder if we can train people not to need to mention the case as they compare. I should look again if you specify upper-case only. > The Type Identifiers for SHA-2 and SHA-3 are chosen so as to cause the > first letter of a SHA-2 digest to always be an M (for Merkle-Damgard and to > remind us of the Rivest/MD5 legacy) and tthe first letter of a SHA-3 digest > will always be a K for Keccak. This was very cute. > Erm no, what people have done there is provide a new attack vector because > most people will only remember the first ten digits of an address at most > and this mnemonic is encouraging people to assume from memory. Anyone who > wants to impersonate the above, just needs to search for a public key whose > first eight digits match and they will probably trick enough people to be > interesting. > So I decided to encourage people not to do this and then thought, what if > they could have a shorter fingerprint that was just as strong. Interesting observation. > The two use cases that I am most tempted to add are representations for > public and private key literals. > PRO: One spec fits all. > CON: Even 25519 keys are long do we read them out over the phone? Perhaps > we should consider Base64? No, but being able to scan QR codes with public keys is important. DPP needs/uses this already. > The first is to add a Type indicator PKIX (112 = P) which would be > followed by a PKIX KeyInfo block. This would be encoded in Base32. This > would look something like this for an Ed25519 key: On the subject of Subject Key Identifier, which you have created a MIME type, RFC7469, section 2.4 also gets close to this. > PB5S-R4AJ-3FBT-7NHO-T26Z-2E6Y-WFH4-SAQQ-RY7F-Q7UU-URHU-VCDB-HALY-LNCG > The second would be to do the above in Base64 but use a type indicator that > gives an initial letter in Base64: I don't think that reading base64 over the phone will ever be a thing. Validating (visually) that a QR scan worked right will be a thing. I prefer to keep it all in base32. -- Michael Richardson <mcr+IETF@sandelman.ca>, Sandelman Software Works -= IPv6 IoT consulting =-
- [Mathmesh] UDF Design notes Phillip Hallam-Baker
- Re: [Mathmesh] UDF Design notes Michael Richardson
- Re: [Mathmesh] UDF Design notes Phillip Hallam-Baker
- Re: [Mathmesh] UDF Design notes Phillip Hallam-Baker
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