PuTTY bug ppk-empty-comment

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summary: Trouble with empty PPK key comments
class: bug: This is clearly an actual problem we want fixed.
difficulty: fun: Just needs tuits, and not many of them.
priority: high: This should be fixed in the next release.
absent-in: 0.52
present-in: 0.53b 2002-10-07 2003-01-04 2003-06-29
fixed-in: 2003-10-13 8e2fd15bd598f3586a2eb36b460d21d77de94db4 (0.54)

Certain forms of empty key comment in PPK files can cause PuTTY to throw an assertion failure (terminal.c, line 3769, len > 0 for 0.53b) (and possibly crash?). Apparently such files can be generated by PuTTYgen.

Update (JTN): I've reproduced this with PuTTY and PuTTYgen 2003-06-29, connecting to "SSH-1.99-OpenSSH_3.4p1 Debian 1:3.4p1-1" with SSH-2 and a passphrase'd RSA2 key which was configured on the server. No crash. The comment part of the PPK file looks like:

0030                         43 6f 6d 6d 65 6e 74 3a           Comment:
0040 20 0d 0a                                           ..             

Update: I've added robustness improvements to everything lurking behind from_backend(), and removed the assertions, so this should be fixed now.

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(last revision of this bug record was at 2016-12-27 11:40:22 +0000)