Openssh-format private keys exported from putty fail to parse

[quexten]

Hi,

putty (putty-gen) apparently encodes keys (somehow) differently to openssh when exporting to the openssh format. These keys fail to parse with the ssh-key crate with Encoding(Pem(Base64(InvalidEncoding))), but parse fine with openssh:

RSA:

-----BEGIN OPENSSH PRIVATE KEY-----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-----END OPENSSH PRIVATE KEY-----

Ed25519:

-----BEGIN OPENSSH PRIVATE KEY-----
b3BlbnNzaC1rZXktdjEAAAAABG5vbmUAAAAEbm9uZQAAAAAAAAABAAAAMwAAAAtz
c2gtZWQyNTUxOQAAACDp0/9zFBCyZs5BFqXCJN5i1DTanzPGHpUeo2LP8FmQ9wAA
AKCyIXPqsiFz6gAAAAtzc2gtZWQyNTUxOQAAACDp0/9zFBCyZs5BFqXCJN5i1DTa
nzPGHpUeo2LP8FmQ9wAAAEDQioomhjmD+sh2nsxfQLJ5YYGASNUAlUZHe9Jx0p47
H+nT/3MUELJmzkEWpcIk3mLUNNqfM8YelR6jYs/wWZD3AAAAEmVkZHNhLWtleS0y
MDI0MTExOAECAwQFBgcICQoL
-----END OPENSSH PRIVATE KEY-----

One notable difference is that these keys have a linewidth of 64 whereas openssh uses 70.
Re-formatting the keys to be linewidth 70 in a text editor leads to an "Encoding(Length)" error.

[tarcieri]

This appears to be a dup of #195 which was fixed in #252

[tarcieri]

Reopening because:

Re-formatting the keys to be linewidth 70 in a text editor leads to an "Encoding(Length)" error.

[Eugeny]

This is due to the padding length being over 8 bytes ("block size" for no-encryption cipher??) for unencrypted keys that PuTTY generates for some reason

[Eugeny]

The padding seems to correctly contain a number seq as per format ([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]) - just too many of them

[Eugeny]

After bruteforcing through possible padding lengths with puttygen by changing the comment length, it appears that puttygen is using 16 as "block size" for unencrypted keys.