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Fix OpenSSH encoding of Ed25519/Ed448 #5520

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Merged
HansN merged 1 commit into from
Jan 13, 2022
Merged

Fix OpenSSH encoding of Ed25519/Ed448 #5520

HansN merged 1 commit into from
Jan 13, 2022

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@jjcarstens
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@jjcarstens jjcarstens commented Dec 15, 2021

Encoding of OpenSSH Key V1 is technically listed as an experimental feature so this isn't the most crucial. But in playing with it I discovered the encoding is incorrect when writing the "encrypted" section of Ed25519/Ed448 keys

Currently, we only write the 32 bytes of the Private key. However, the encrypted section is 64 bytes of a "secret" key which includes the private key and public key combined. This is confirmed through a few sources:

This experimental feature seems untested (or I haven't found the right place) so below is some console output. Note the current behavior is missing the private key binary when decoding a key generated from ssh_file:encode/2. Happy to add tests if there is an expected place

Current behavior (from console) 
1> {Pub, Priv} = crypto:generate_key(eddsa, ed25519).
{<<215,125,77,247,17,30,232,110,152,159,130,127,155,239,
   39,228,237,136,11,249,153,125,21,51,185,76,228,190,...>>,
 <<194,101,237,100,119,133,35,110,181,76,5,224,211,5,192,
   70,54,228,216,2,165,220,229,249,243,202,130,...>>}

2> Keypairs = [{{ed_pri, ed25519, Pub, Priv}, <<"[email protected]">>}].
[{{ed_pri,ed25519,
          <<215,125,77,247,17,30,232,110,152,159,130,127,155,239,39,
            228,237,136,11,249,153,125,21,51,...>>,
          <<194,101,237,100,119,133,35,110,181,76,5,224,211,5,192,
            70,54,228,216,2,165,220,229,...>>},
  <<"[email protected]">>}]

3> Encoded = ssh_file:encode([{Keypairs, []}], openssh_key_v1).
<<"-----BEGIN OPENSSH PRIVATE KEY-----\nb3BlbnNzaC1rZXktdjEAAAAABG5vbmUAAAAEbm9uZQAAAAAAAAABAAAAMwAAAAtzc2gt\nZWQyNTUxOQA"...>>

4> ssh_file:decode(Encoded, openssh_key_v1).
[{{ed_pri,ed25519,
          <<215,125,77,247,17,30,232,110,152,159,130,127,155,239,39,
            228,237,136,11,249,153,125,21,51,...>>,
          <<>>},
% NOTE: The missing private Key ^
  []},
 {{ed_pub,ed25519,
          <<215,125,77,247,17,30,232,110,152,159,130,127,155,239,
            39,228,237,136,11,249,153,125,21,...>>},
  []}]
With proposed fix 
1> {Pub, Priv} = crypto:generate_key(eddsa, ed25519).
{<<242,112,197,146,120,78,235,14,133,240,247,77,162,57,45,
   50,179,218,243,60,91,106,214,240,55,84,255,0,...>>,
 <<11,157,146,182,123,184,78,30,164,173,8,76,179,133,19,
   122,197,107,143,105,129,118,194,115,127,23,141,...>>}

2> Keypairs = [{{ed_pri, ed25519, Pub, Priv}, <<"[email protected]">>}].
[{{ed_pri,ed25519,
          <<242,112,197,146,120,78,235,14,133,240,247,77,162,57,45,
            50,179,218,243,60,91,106,214,240,...>>,
          <<11,157,146,182,123,184,78,30,164,173,8,76,179,133,19,
            122,197,107,143,105,129,118,194,...>>},
  <<"[email protected]">>}]

3> Encoded = ssh_file:encode([{Keypairs, []}], openssh_key_v1).
<<"-----BEGIN OPENSSH PRIVATE KEY-----\nb3BlbnNzaC1rZXktdjEAAAAABG5vbmUAAAAEbm9uZQAAAAAAAAABAAAAMwAAAAtzc2gt\nZWQyNTUxOQA"...>>

4> ssh_file:decode(Encoded, openssh_key_v1).
[{{ed_pri,ed25519,
          <<242,112,197,146,120,78,235,14,133,240,247,77,162,57,45,
            50,179,218,243,60,91,106,214,240,...>>,
          <<11,157,146,182,123,184,78,30,164,173,8,76,179,133,19,
            122,197,107,143,105,129,118,194,...>>},
  []},
 {{ed_pub,ed25519,
          <<242,112,197,146,120,78,235,14,133,240,247,77,162,57,45,
            50,179,218,243,60,91,106,214,...>>},
  []}]
Proposed fix with fixture 
1> {ok,Encoded} = file:read_file(<<"lib/ssh/test/ssh_algorithms_SUITE_data/id_ed25519">>).
{ok,<<"-----BEGIN OPENSSH PRIVATE KEY-----\nb3BlbnNzaC1rZXktdjEAAAAABG5vbmUAAAAEbm9uZQAAAAAAAAABAAAAMwAAAAtzc2gtZW\nQ"...>>}

2> ssh_file:decode(Encoded, openssh_key_v1).
[{{ed_pri,ed25519,
          <<230,244,255,63,128,45,8,56,169,176,28,180,175,146,97,45,
            75,101,241,209,20,106,80,58,...>>,
          <<115,11,246,118,88,98,97,103,121,119,180,128,103,81,206,
            131,9,186,126,149,118,54,201,...>>},
  []},
 {{ed_pub,ed25519,
          <<230,244,255,63,128,45,8,56,169,176,28,180,175,146,97,
            45,75,101,241,209,20,106,80,...>>},
  []}]

@IngelaAndin IngelaAndin added the team:PS Assigned to OTP team PS label Dec 20, 2021
@HansN HansN added the bug Issue is reported as a bug label Jan 10, 2022
HansN
HansN reviewed Jan 11, 2022
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@jjcarstens jjcarstens force-pushed the fix-openssh-v1-encode-ed branch from 91cb0d1 to 032780e Compare January 11, 2022 15:31
@HansN HansN added the testing currently being tested, tag is used by OTP internal CI label Jan 11, 2022
@HansN HansN merged commit 567f5a3 into erlang:maint Jan 13, 2022
@jjcarstens jjcarstens deleted the fix-openssh-v1-encode-ed branch January 13, 2022 16:16
@HansN
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HansN commented Jan 13, 2022

Thanks for the PR! Always nice to get errors fixed!

@HansN HansN removed the testing currently being tested, tag is used by OTP internal CI label Jan 13, 2022
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