Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 2CBD5868 for ; Mon, 3 Dec 2018 18:28:06 +0000 (UTC) X-Greylist: whitelisted by SQLgrey-1.7.6 Received: from mail-qk1-f170.google.com (mail-qk1-f170.google.com [209.85.222.170]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 66575834 for ; Mon, 3 Dec 2018 18:28:05 +0000 (UTC) Received: by mail-qk1-f170.google.com with SMTP id r71so7951047qkr.10 for ; Mon, 03 Dec 2018 10:28:05 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:from:date:message-id:subject:to; bh=qYAwNrhXK77rEKna1BaM/S5zDwmTbpM1xW0stFACKnI=; b=bmksbyJTI7OQoQrog/0G28ufmUeeKPOvrZHlv1ucb68tc6BS3g9/PSAdKCWjlrBBKo OwhOtqPOUi5UWKpRIra/08PNGwogp7PHU2nLYTfyzZHhqGu4mxg1AovXZ4DLkfbvjv7P 5gm6YhcGrLN1D048FEcfZ8MMN/kRFjDZKb0xo1kCicWvYQpPsPb4VDpXS0sQ61k0UfxE jqhuTW45zAN2XsXcwLfhkells1QgDfEhowiUM0z37I0QeOqop2rrpszejPwJlNy7FBKt a/4l1I9gG2J8uLVvAxnevrMY8SbhQF9FfkdjWtzIzAZRak0EFl6WvtahTYgj6Au6Vmdb SVow== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:from:date:message-id:subject:to; bh=qYAwNrhXK77rEKna1BaM/S5zDwmTbpM1xW0stFACKnI=; b=FCbJs+r811rZ+4MHd9ngMUOJzMofznn/35KjvB5m+WSPK+piBTPAQAF/ROse+gcu0k N6mwBuQpcoiHFTsnL3fBYRb4QiZ9CtiqI/I6p7VJo7DuXh7JLLIvug4O3d12WxNifB2E iVcGz3Q26grcEbdkglPC93Iv1Q8ia8jw10rv26f1/PqAblYgsRffIIo1exhHIym3AvSq DoZOCkU3dqI7jcla8SYIso9f/foVbzsuKRD36ehY06meH1amuBIHmVwkDZrowahCUBIj 9Pdgq1Bcm7S4Lbq8CluJcKvPVAfemUXrBeLfrE/Ctculpw/5MrmI56ckiuen0hcpJ7pJ jTqA== X-Gm-Message-State: AA+aEWY9Ax5VXGUeD4kOCCkRwYKA1wUANXsVS/lC/lBaD0gC+vppMKzf 5bSJ+LrzwaknFQMaNM7VjmY4AYJ22gq9K1O4Sxys7dTbUC4= X-Google-Smtp-Source: AFSGD/Vul4Oj51uEPb0XAZfnc6hY7V6rI2/naYqLxBcaWlE5Qs925hJi/p8MXDp8aDVzISzmV6vRrcqa28PTPSdWpS4= X-Received: by 2002:ae9:e102:: with SMTP id g2mr14948797qkm.343.1543861684250; Mon, 03 Dec 2018 10:28:04 -0800 (PST) MIME-Version: 1.0 From: Steven Hatzakis Date: Mon, 3 Dec 2018 20:27:52 +0200 Message-ID: To: bitcoin-dev@lists.linuxfoundation.org Content-Type: multipart/alternative; boundary="00000000000045ae78057c224fa3" X-Spam-Status: No, score=-2.0 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, FREEMAIL_FROM, HTML_MESSAGE, RCVD_IN_DNSWL_NONE autolearn=ham version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on smtp1.linux-foundation.org X-Mailman-Approved-At: Mon, 03 Dec 2018 18:44:44 +0000 Subject: [bitcoin-dev] Proposal for Palindromic (Reversible) Mnemonics X-BeenThere: bitcoin-dev@lists.linuxfoundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Bitcoin Protocol Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 03 Dec 2018 18:28:06 -0000 --00000000000045ae78057c224fa3 Content-Type: text/plain; charset="UTF-8" Hi All, I've developed a method to check if a mnemonic is also valid when the words are put into reverse order (not the entropy), where a given 12 or 24-word mnemonic could be valid both in little endian and big endian format. I've coined these "Palindromic Mnemonics", but perhaps more user-friendly is "reversible mnemonics." Purpose: A checksum-valid reversible mnemonic allows two separate vaults to be connected to the same mnemonic string of words, where all a users must do is enter the words in reverse order (the last word becomes first, second to last becomes second, and so on) to access the secondary (reversed words) vault. This utility could provide multiple use-cases, including related to combinations with passphrases and plausible deniability, as well as conveniences for those wishing to use a separate vault tied to the same string of words. Security: For any randomly generated 12-word mnemonic (128-bits of security) the chances of it also being reversible are 1/16 (I believe), as a total of 4 bit positions must be identical (4 bits from the normal mnemonic and another 4 bits from the reversed string must match). For a 24-word mnemonic, those values increase to 8 bits which need to match 8 bits from the reversed string, leading to about 1 in every 256 mnemonics also being reversible. While the message space of valid reversible mnemonics should be 2^124 for 12 words, that search must still be conducted over a field of 2^128, as the hash-derived checksum values otherwise prevent a way to deterministically find valid reversible mnemonics without first going through invalid reversible ones to check. I think others should chime in on whether they believe there is any security loss, in terms of entropy bits (assuming the initial 128 bits were generated securely). I estimate at most it would be 4-bits of loss for a 12-word mnemonic, but only if an attacker had a way to search only the space of valid reversible mnemonics (2**124) which I don't think is feasible (could be wrong?). There could also be errors in my above assumptions, this is a work in progress and sharing it here to solicit initial feedback/interest. I've already written the code that can be used for testing (on GitHub user @hatgit), and when run from terminal/command prompt it is pretty fast to find a valid reversible mnemonics, whereas on IDLE in Python on a 32-bit and 64-bit machine it could take a few seconds for 12 words and sometimes 10 minutes to find a valid 24-word reversible mnemonic. Example 12 words reversible (with valid checksum each way): limit exact seven clarify utility road image fresh leg cabbage hint canoe And Reversed: canoe hint cabbage leg fresh image road utility clarify seven exact limit Example 24 reversible: favorite uncover sugar wealth army shift goose fury market toe message remain direct arrow duck afraid enroll salt knife school duck sunny grunt argue And reversed: argue grunt sunny duck school knife salt enroll afraid duck arrow direct remain message toe market fury goose shift army wealth sugar uncover favorite My two questions 1) are how useful could this be for you/users/devs/service providers etc.. and 2) is any security loss occurring and whether it is negligible or not? Best regards, Steven Hatzakis --00000000000045ae78057c224fa3 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable

Hi Al= l,=C2=A0

I've develo= ped a method to check if a mnemonic is also valid when the words are put in= to reverse order (not the entropy), where a given 12 or 24-word mnemonic co= uld be valid both in little endian and big endian format. I've coined t= hese "Palindromic Mnemonics", but perhaps more user-friendly is &= quot;reversible mnemonics."

Purpose:
A checksum-valid reversible mnemonic= allows two separate vaults to be connected to the same mnemonic string of = words, where all a users must do is enter the words in reverse order (the l= ast word becomes first, second to last becomes second, and so on) to access= the secondary (reversed words) vault. This utility could provide multiple = use-cases, including related to combinations with passphrases and plausible= deniability, as well as conveniences for those wishing to use a separate v= ault tied to the same string of words.

Securi= ty:
For any randomly generated 12= -word mnemonic (128-bits of security) the chances of it also being reversib= le are 1/16 (I believe), as a total of 4 bit positions must be identical (4= bits from the normal mnemonic and another 4 bits from the reversed string = must match). For a 24-word mnemonic,=C2=A0those values increase to 8 bits w= hich need to match 8 bits from the reversed string, leading to about 1 in e= very 256 mnemonics also being reversible. While the message space of valid = reversible mnemonics should be 2^124 = for 12 words, that search must still be conducted over a field of 2<= span style=3D"box-sizing:border-box;font-weight:600">^128, as the ha= sh-derived checksum values otherwise prevent a way to deterministically fin= d valid reversible mnemonics without first going through invalid reversible= ones to check. I think others should chime in on whether they believe ther= e is any security loss, in terms of entropy bits (assuming the initial 128 = bits were generated securely). I estimate at most it would be 4-bits of los= s for a 12-word mnemonic, but only if an attacker had a way to search only = the space of valid reversible mnemonics (2**124) which I don't think is= feasible (could be wrong?). There could also be errors in my above assumpt= ions, this is a work in progress and sharing it here to solicit initial fee= dback/interest.

I've= already written the code that can be used for testing (on GitHub user @hat= git), and when run from terminal/command prompt it is pretty fast to find a= valid reversible mnemonics, whereas on IDLE in Python on a 32-bit and 64-b= it machine it could take a few seconds for 12 words and sometimes 10 minute= s to find a valid 24-word reversible mnemonic.=C2=A0

Example 12 words re= versible (with valid checksum each way):

limit exact seven clarify = utility road image fresh leg cabbage hint canoe

And Reversed:
canoe hint cabbage leg fresh image road utility clarify seven exact limit<= br>

Example 24 reversible:

favorite uncover sugar wealth army= shift goose fury market toe message remain direct arrow duck afraid enroll= salt knife school duck sunny grunt argue

And reversed:

argue grunt sunny = duck school knife salt enroll afraid duck arrow direct remain message toe m= arket fury goose shift army wealth sugar uncover favorite


My two questions 1) are how useful could this= be for you/users/devs/service providers etc.. and 2) is any security loss = occurring and whether it is negligible or not?

Best regards,


Steven=C2=A0Hatzakis=C2=A0
--00000000000045ae78057c224fa3--