Re: [fossil-users] OT: security/entropy (was Re: New Fossil user experiences)
On Jul 15, 2018, at 8:47 AM, Joerg Sonnenberger wrote: > > On Sat, Jul 14, 2018 at 05:24:26PM -0600, Warren Young wrote: >> On Jul 14, 2018, at 2:18 PM, Joerg Sonnenberger wrote: >>> >>> On Fri, Jul 13, 2018 at 03:27:14PM -0600, Warren Young wrote: For example, 100 a’s requires a 7-bit run-length plus zero bits for our only code point >>> >>> You need more than zero bits to encode the original a though. >> >> There’s only one letter in this alphabet, so all we need is a run length >> to say how many of them there are in our message. > > You are kind of making my point for me. You are adding a priori > knowledge of a single letter alphabet in a context where this assumption > makes no natural sense. By that line of reasoning, you can also assume > knowledge that passwords are always a multiple of size n and the entropy > would be near zero… I’m taking inspiration from Huffman coding here, so you actually need 7 bits for the length prefix + sizeof(dictionary_with_one_entry). ___ fossil-users mailing list fossil-users@lists.fossil-scm.org http://lists.fossil-scm.org:8080/cgi-bin/mailman/listinfo/fossil-users
Re: [fossil-users] OT: security/entropy (was Re: New Fossil user experiences)
On Sat, Jul 14, 2018 at 05:24:26PM -0600, Warren Young wrote: > On Jul 14, 2018, at 2:18 PM, Joerg Sonnenberger wrote: > > > > On Fri, Jul 13, 2018 at 03:27:14PM -0600, Warren Young wrote: > >> > >> For example, 100 a’s requires a 7-bit run-length plus zero bits for our > >> only code point > > > > You need more than zero bits to encode the original a though. > > There’s only one letter in this alphabet, so all we need is a run length > to say how many of them there are in our message. You are kind of making my point for me. You are adding a priori knowledge of a single letter alphabet in a context where this assumption makes no natural sense. By that line of reasoning, you can also assume knowledge that passwords are always a multiple of size n and the entropy would be near zero... Joerg ___ fossil-users mailing list fossil-users@lists.fossil-scm.org http://lists.fossil-scm.org:8080/cgi-bin/mailman/listinfo/fossil-users
Re: [fossil-users] OT: security/entropy (was Re: New Fossil user experiences)
On Jul 14, 2018, at 2:18 PM, Joerg Sonnenberger wrote: > > On Fri, Jul 13, 2018 at 03:27:14PM -0600, Warren Young wrote: >> >> For example, 100 a’s requires a 7-bit run-length plus zero bits for our >> only code point > > You need more than zero bits to encode the original a though. There’s only one letter in this alphabet, so all we need is a run length to say how many of them there are in our message. Another way to look at it is that a bit encodes one of two states, but we only have one state in this example, so we don’t need a whole bit to encode it. If the example were a’s or no-a’s, then you’d have two states, and thus need to encode it with bits. But materially, that’s no different from an a’s or b’s system, which also requires one bit per state. ___ fossil-users mailing list fossil-users@lists.fossil-scm.org http://lists.fossil-scm.org:8080/cgi-bin/mailman/listinfo/fossil-users
Re: [fossil-users] OT: security/entropy (was Re: New Fossil user experiences)
On 7/14/18, Joerg Sonnenberger wrote: > If you can take the output > of any modern CPRNG as hex and don't get 4bpc, the entropy estimator is > broken. I've always understood the output of entropy estimators to me "the entropy is no greater than this", which is somewhat easier to define, since you get your choice of models. -- D. Richard Hipp d...@sqlite.org ___ fossil-users mailing list fossil-users@lists.fossil-scm.org http://lists.fossil-scm.org:8080/cgi-bin/mailman/listinfo/fossil-users
Re: [fossil-users] OT: security/entropy (was Re: New Fossil user experiences)
On Fri, Jul 13, 2018 at 02:49:52PM -0700, Jungle Boogie wrote: > On Fri 13 Jul 2018 4:22 PM, David Mason wrote: > > So I guess this is what Warren had in mind. Posting this in case it helps > > somebody on the list. > > > > Taking this offtopic a little bit more...let's talk about VPNs. > > Don't use PPTP and don't get tangled up in ipsec configuration hell. > > Be happy with wireguard! https://www.wireguard.com > > It runs on everything but Windows (Linux, *BSD, MacOS, Andriod, iphone). > There's > no passwords to share and the public keys are easily, easily distributed. While I know that the underlaying cryptographic primites are sound, a lot of the wireguard description is overhyped and misguided. Code doesn't become more secure by moving it into the kernel and a VPN daemon does a lot more than just dealing with key exchange. I'd strongly advice to look at the ingredience list of the KoolAid... Joerg ___ fossil-users mailing list fossil-users@lists.fossil-scm.org http://lists.fossil-scm.org:8080/cgi-bin/mailman/listinfo/fossil-users
Re: [fossil-users] OT: security/entropy (was Re: New Fossil user experiences)
On Fri, Jul 13, 2018 at 03:27:14PM -0600, Warren Young wrote: > On Jul 13, 2018, at 3:13 PM, Warren Young wrote: > > > > Now paste in an equivalent number of ‘a’ characters, and you get 0 bits of > > entropy. Strictly speaking, you get 1 bit of entropy for the whole > > message, but it shows 0 because the calculator is rounding the result off > > to 3 significant figures. > > Hmmm…we also need something like a run-length prefix to reconstruct the > message, so this calculator is undershooting slightly. > > For example, 100 a’s requires a 7-bit run-length plus zero bits for our > only code point, so we should get 0.07 bpc, within this calculator’s > apparent precision even without dealing with roundoff errors. You need more than zero bits to encode the original a though. Frankly, this seems like a bit of pseudo-math to me. The very definition of entropy depends on the context. So a question of "how much entropy does this string have" is seriously underdefined. If you can take the output of any modern CPRNG as hex and don't get 4bpc, the entropy estimator is broken. Joeg ___ fossil-users mailing list fossil-users@lists.fossil-scm.org http://lists.fossil-scm.org:8080/cgi-bin/mailman/listinfo/fossil-users
Re: [fossil-users] OT: security/entropy (was Re: New Fossil user experiences)
On Fri 13 Jul 2018 4:22 PM, David Mason wrote: > So I guess this is what Warren had in mind. Posting this in case it helps > somebody on the list. > Taking this offtopic a little bit more...let's talk about VPNs. Don't use PPTP and don't get tangled up in ipsec configuration hell. Be happy with wireguard! https://www.wireguard.com It runs on everything but Windows (Linux, *BSD, MacOS, Andriod, iphone). There's no passwords to share and the public keys are easily, easily distributed. > Thanks ../Dave ___ fossil-users mailing list fossil-users@lists.fossil-scm.org http://lists.fossil-scm.org:8080/cgi-bin/mailman/listinfo/fossil-users
Re: [fossil-users] OT: security/entropy (was Re: New Fossil user experiences)
On Jul 13, 2018, at 3:13 PM, Warren Young wrote: > > 2. Add a dollar sign to the message, and bpc goes up a bit. (This conflicts > with your report that adding a special character didn’t change it, but it did > for me.) I just realized where the discrepancy comes from: you *replaced* one character of the original message with a special character, so the resulting alphabet size didn’t change, whereas I *added* a non-alphanumeric character to the message, which did change my alphabet size. This calculator doesn’t know about “special characters,” all it knows about are the number of unique input symbols it is given and how that relates to the total message size. ___ fossil-users mailing list fossil-users@lists.fossil-scm.org http://lists.fossil-scm.org:8080/cgi-bin/mailman/listinfo/fossil-users
Re: [fossil-users] OT: security/entropy (was Re: New Fossil user experiences)
On Jul 13, 2018, at 3:13 PM, Warren Young wrote: > > Now paste in an equivalent number of ‘a’ characters, and you get 0 bits of > entropy. Strictly speaking, you get 1 bit of entropy for the whole message, > but it shows 0 because the calculator is rounding the result off to 3 > significant figures. Hmmm…we also need something like a run-length prefix to reconstruct the message, so this calculator is undershooting slightly. For example, 100 a’s requires a 7-bit run-length plus zero bits for our only code point, so we should get 0.07 bpc, within this calculator’s apparent precision even without dealing with roundoff errors. Still, it’s good enough for our purposes here, which is to make it clear to us that if you use a hex string as a passphrase, you need 128 characters of it to fully justify the use of 256-bit symmetric encryption. ___ fossil-users mailing list fossil-users@lists.fossil-scm.org http://lists.fossil-scm.org:8080/cgi-bin/mailman/listinfo/fossil-users
Re: [fossil-users] OT: security/entropy (was Re: New Fossil user experiences)
On Jul 13, 2018, at 2:22 PM, David Mason wrote: > > Acgq75VpCWjdsJaa5abe9JeX3I (don't worry, this isn't a real password to > anything) > > …I fed this through an online entropy calculator and got 4.29 bits of Shannon > entropy That calculator is giving you bits *per character*. You can see this several ways: 1. Double the message and the bits per character doesn’t change because the size of the source alphabet doesn’t change. 2. Add a dollar sign to the message, and bpc goes up a bit. (This conflicts with your report that adding a special character didn’t change it, but it did for me.) 3. Turn on the calculator’s case folding option and the bpc value goes down a bit. One key realization you should get from this calculator is that ASCII text is not 7 or 8 bits of entropy per character. It simply is not, because not all characters in the source text are equally likely. Many code points may never be used in a given corpus. Another realization is that a random blob of hex noise should asymptotically approach 4 bpc, since each character is 4 bits of data, and the data are supposed to be evenly distributed across the code space. Here’s some noise from grc.com/pass: C79683189EFBEBEC30A4C1A6D733F0242FB48E2582F3B2E7581D85E91E0A2FA5 The initial value is 3.91, and pasting it in a bunch of times does increase the value towards 4, suggesting it’s got pretty good entropy. Now paste in an equivalent number of ‘a’ characters, and you get 0 bits of entropy. Strictly speaking, you get 1 bit of entropy for the whole message, but it shows 0 because the calculator is rounding the result off to 3 significant figures. > So I tried: > dd if=/dev/random bs=100 count=1|od -c > and the result only gave 5.00 bits That’s plausible. With a much larger sample, the result should approach 7, 8, 16, or 21, depending on your local character set size. (Respectively: pure ASCII, ISO 8859 or similar, UCS-2 and full Unicode.) Now see if you can guess the asymptotic ideal for this slightly different command: $ dd if=/dev/random bs=100 count=1 | od Spoiler below. ……….. 3, because the output is restricted to octal, thus 3 bpc. ___ fossil-users mailing list fossil-users@lists.fossil-scm.org http://lists.fossil-scm.org:8080/cgi-bin/mailman/listinfo/fossil-users
[fossil-users] OT: security/entropy (was Re: New Fossil user experiences)
I use a password generator of my own design - basically takes the userid, concatenated with a fairly long secret phrase, and then I do SHA1 and convert it to base64, giving a password like: Acgq75VpCWjdsJaa5abe9JeX3I (don't worry, this isn't a real password to anything) After Warren's comment about wanting 256 bits of entropy, I fed this through an online entropy calculator (https://planetcalc.com/2476/ - I wouldn't feed a real password through anything on the web!), and got 4.29 bits of Shannon entropy (replacing a character with a special character didn't change the number). Calculating it on a whole web page only gave 5.41. So I tried: dd if=/dev/random bs=100 count=1|od -c and the result only gave 5.00 bits So I'm guessing this isn't what he meant. http://rumkin.com/tools/password/passchk.php does a version and it says my fake password above is 130 bits. The 800 bits of random converted to hex gives 779 bits So I guess this is what Warren had in mind. Posting this in case it helps somebody on the list. Thanks ../Dave ___ fossil-users mailing list fossil-users@lists.fossil-scm.org http://lists.fossil-scm.org:8080/cgi-bin/mailman/listinfo/fossil-users
