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+++ This bug was initially created as a clone of Bug #156371 +++ These issues were reported to secalert@redhat.com by David Martin. - If you click the "generate keys" button in system-config-network-gui (rhel 4), as seems the prudent thing to do, then it generates 24 bytes/characters of key for the connection. At 8 bits/byte that's 24*8=192 bits, which is appropriate for 3-key 3DES keys. But each of these 24 characters is chosen from [0-9a-f], so each char only contains 4 bits of information -- and those 24 characters only result in a key that has 24*4=96 bits of entropy, half of the desired amount, and also 16 bits less than the standard minimum 112 bits for 3DES. - The same utility appears to use the same keys in both directions of the connection, even though it assigns them different SPIs. Using the same key for multiple directions in a connection is well known to lead to simple cut-and-paste attacks and other vulnerabilities. - Presumably for ease of configuration, the utilities derive the SPIs from the keys themselves. But these SPIs leak information about the keys. Here's an line from the Python code that generates the SPIs: conf["SPI_AH_IN"] = str(zlib.crc32(self.AHKey + "IN", 0) & 0x7FFFFFFF) CRC32 is *not* a one-way function. The resulting SPI contains a lot of information about the key it refers to. And SPIs are transmitted in cleartext in IPsec. I'm not sure exactly how many bits this leaks, but combined with the inherent weakness of the keys above, this could well lead to a practical procedure for extracting keys from active connections -- one that would succeed in the order of days rather than millenia. Again, these problems are all in the Red Hat configuration utilities. IPsec is horribly complicated so it's natural that administrators will lean on your configuration utilities to set things up. There is a moment of reprieve here in that because the SPI IN/OUT thing is broken, there probably aren't many vulnerable connections actually being used. So when you address that problem, please make sure you fix these security weaknesses too.
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