Created attachment 1651 [details]
Suggested fix to always print out randomart based on MD5

If ssh-keygen is used with both the -B option (to print the bubblebabble digest of a key) and the -v option (which prints the randomart), then the randomart will be different than if the -B option was not used.

Steps to reproduce:
1) Generate a key:
<blockquote>
# ssh-keygen -v -t rsa -b 2048 -f /tmp/garbage
Generating public/private rsa key pair.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /tmp/garbage.
Your public key has been saved in /tmp/garbage.pub.
The key fingerprint is:
eb:19:8d:76:9e:d8:ee:63:6a:3c:9f:19:d4:37:1c:cc user@hostname
The key's randomart image is:
+--[ RSA 2048]----+
|                 |
|             o   |
|              E  |
|           . . . |
|        S . . +  |
|         =   . . |
|       .= +      |
|       o+Bo=     |
|       .=BX.     |
+-----------------+
</blockquote>

2) Display the fingerprint with ssh-keygen:
<blockquote>
# ssh-keygen -v -l -f /tmp/garbage
2048 eb:19:8d:76:9e:d8:ee:63:6a:3c:9f:19:d4:37:1c:cc /tmp/garbage.pub (RSA)
+--[ RSA 2048]----+
|                 |
|             o   |
|              E  |
|           . . . |
|        S . . +  |
|         =   . . |
|       .= +      |
|       o+Bo=     |
|       .=BX.     |
+-----------------+
</blockquote>

3) Display the fingerprint and bubblebabble with ssh-keygen:
<blockquote>
# ssh-keygen -B -v -l -f /tmp/garbage
2048 xecen-telud-badez-sozic-hopyd-cacov-tanig-dimov-monef-sytym-haxax /tmp/garbage.pub (RSA)
+--[ RSA 2048]----+
|  .+.. ....+     |
|... = * =.=      |
|o  E * B *..     |
|. + = . =.o      |
| . .    S.       |
|                 |
|                 |
|                 |
|                 |
+-----------------+
</blockquote>

The problem is that bubblebabble uses the SHA1 digest to generate the fingerprint, while randomart usually uses the MD5 digest. ssh-keygen.c will generate randomart with the SHA1 digest if it is also producing bubblebabble output.

This problem was found on openssh v5.2p1. It also appears to be in OpenBSD's ssh-keygen.c v1.173.

Diff for fix attached.